Tess Saxton-Fox
University of Illinois at Urbana-Champaign
2.00pm Wednesday 22 June 2022
Online Event (2022 Australasian Fluid Mechanics Seminar Series)
Pejman Tahmasebi
University of Wyoming
4.00pm Wednesday 15 June 2022
Online Event (2022 Australasian Fluid Mechanics Seminar Series)
Josué Sznitman
Technion
5.00pm Wednesday 08 June 2022
Online Event (2022 Australasian Fluid Mechanics Seminar Series)
Angeliki Laskari
TU Delft
4.00pm Wednesday 01 June 2022
Online Event (2022 Australasian Fluid Mechanics Seminar Series)
Susann Beier
UNSW
4.00pm Wednesday 25 May 2022
Online Event (2022 Australasian Fluid Mechanics Seminar Series)
2022 AFMSS: Earwax and a Wombat's Cube-Shaped Poo
David Hu
Georgia Institute of Technology
1.00pm Wednesday 18 May 2022
Online Event (2022 Australasian Fluid Mechanics Seminar Series)
In this talk, I will discuss two poorly understood biomaterials, earwax and wombat feces. For centuries, humans have invented a number of devices
to remove accumulated earwax. We perform rheometer experiments and other assays that elucidate some of the adaptive properties of earwax in mammals.
Earwax has low adhesion to the feet of ants, which reduces their ability to crawl into the ear, a problem for many people in the tropics. Earwax
ages in the ear, leading to cracking and renewal on a regular basis. Wombat feces has a characteristic cube-shape, unique among mammals. We discuss
the drying dynamics and peristalsis that lead to the generation of these shapes. The audience will learn how to design experiments on exotic
biomaterials.
Dr. David Hu is a mechanical engineer who studies the interactions of animals with water. He has discovered how dogs shake dry, how insects walk on
water, and how eyelashes protect the eyes from drying. Originally from Rockville, Maryland, he earned degrees in mathematics and mechanical engineering
from M.I.T., and is now Professor of Mechanical Engineering and Biology and Adjunct Professor of Physics at Georgia Tech. He serves on the editorial
boards for Proceedings of the Royal Society B: Biological Sciences, Scientific Reports, and Journal of Experimental Biology. His research has been
featured in The Economist, The New York Times, Saturday Night Live, and Highlights for Children. He is a recipient of the National Science Foundation
CAREER award for young scientists, the Ig Nobel Prize in Physics (twice), and the Pineapple Science Prize (the Ig Nobel of China). He is the author of
the book "How to walk on water and climb up walls," which earned the American Institute of Physics Science Communication award and was finalist for the
AAAS/Subaru Prize for Excellence in Young Adult Science Books. He lives with his wife and two children in Atlanta, Georgia.
2022 AFMSS: The Superharmonic Cascade of Internal Tides
Bruce Sutherland
University of Alberta
3.00pm Wednesday 11 May 2022
Online Event (2022 Australasian Fluid Mechanics Seminar Series)
Propagating in non-uniform stratification, the internal tide excites superharmonics with double the horizontal wavenumber of the internal
tide and nearly double the frequency. Particularly in the tropics, where the Coriolis parameter is small, the superharmonics are nearly
resonant with the internal tide, growing to large amplitude and themselves exciting super-harmonics. This work will present theory, in the
form of coupled ordinary differential equations, which predict that the superharmonic cascade leads to the formation of a solitary wave-train.
The results are in excellent agreement with fully nonlinear numerical simulations. For long waves in strong near-surface stratification, the
results agree well with the prediction of shallow water theory including rotation through the Ostrovsky equation. The predictions of the
Miyata-Choi-Camassa model including rotation are qualitatively similar, but less quantitatively accurate. Our theory thus provides new insight
into the dynamics leading to the nonlinear steepening of the internal tide, and it provides an efficient algorithm for predicting the evolution
of the waves going beyond the restrictions of shallow water theory.
Bruce Sutherland received his PhD in atmospheric science in the Department of Physics at the University of Toronto in 1994, then pursued
postdoctoral training in the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge before taking up a position
in 1997 as Assistant Professor in the Department of Mathematics at the University of Alberta. He is now a Professor jointly appointed in the
Departments of Physics and of Earth & Atmospheric Sciences at the University of Alberta. His research combines theory, numerical simulations
and laboratory experiments to examine phenomena occurring in stratified fluids. Main topics include interfacial and vertically propagating
internal waves, the evolution of gravity currents and plumes in stratified fluids, and the transport and deposition of sediments and microplastics
in geophysical flows.
2022 AFMSS: Quest for Equations Beyond the Navier-Stokes
Amit Agrawal
Indian Institute of Technology Bombay
4.00pm Wednesday 04 May 2022
Online Event (2022 Australasian Fluid Mechanics Seminar Series)
There is evidence in the literature as well as experimental data from our lab suggesting that the Navier-Stokes equations are inadequate to
explain several observations with low-pressure gas flows. There seems to be no satisfactory alternative to theoretically describe the flow when
the mean free path of the gas is of the order of the characteristic length scale. The two well established approaches of solving the Boltzmann
equation yield the Burnett and Grad 13-moments equations, which are higher-order transport equations. However, several shortcomings of
these equations are known by now. This motivated us to explore alternate ways to study and derive higher-order transport equations.
techniques (e.g., riblets, compliant walls) as well as active feedback flow control (e.g., opposition control), and provides useful guidelines for the
development of practicable control techniques. In this talk, I will first present experimental results on rarefied gas flow in a sudden expansion. This
flow exhibits several unique features not seen with conventional flows; such as discontinuity in pressure gradient at the junction, and absence of
flow separation yet an enhanced overall pressure drop. This and several other such flows cannot be modeled within the Navier-Stokes equations, and
one can try invoking the higher-order transport equations. Solving higher-order transport equations is however not trivial. Using a novel
iterative approach we could find the first ever analytical solution of the Burnett equations. In the second part of this talk, I will discuss our novel
approach of employing distribution function consistent with Onsager's reciprocity principle to capture non-equilibrium thermodynamics effects,
and the new equations derived in our group. I will present the attractive features of these newly derived OBurnett and O13 equations and some
solutions of these equations. The talk therefore explains the conditions under which the celebrated Navier-Stokes equations fail, and the
way to model the flow under such circumstances.
Prof. Amit Agrawal joined the Indian Institute of Technology (IIT) Bombay in 2004 and is currently an Institute Chair Professor in the
Department of Mechanical Engineering, and Dean of International Relations, IIT Bombay. His research interests are in Micro-scale flows,
Development of novel bio-microdevices, Theoretical fluid mechanics, and Turbulent flows. He has graduated 30 PhDs and advised several postdocs
and Master's students on these and related topics. He has published more than 240 journal articles and filed for a dozen patents with
his students. His primary contributions are in the development of a unique blood plasma separation microdevice and derivation of equations
which (he believes) are more general than the Navier- Stokes equations. A technique for processing data
in turbulent flows is sometimes referred to as Agrawal Decomposition. His insights and novel results on transmission of COVID-19 are
documented as 8 Featured Articles in prestigious journal Physics of Fluids; these articles have been downloaded more than 112,000 times and covered
by 200+ news outlets in more than 50 countries. Prof. Amit Agrawal has authored a well-received book entitled Microscale Flow and Heat
Transfer: Mathematical Modelling and Flow Physics. The work from his lab has appeared on the cover page of prestigious journals such as
Journal of Fluid Mechanics and Physics of Fluids. He serves as Editor-in-Chief of Transactions of INAE and Editor of ASME Journal of Heat
Transfer, and other reputed journals. He is an elected Fellow of the prestigious Indian National Academy of Engineering (INAE), the National
Academy of Sciences India, and Indian Academy of Sciences. He has been interviewed by All India Radio, Cooling India magazine, and web-series
(such as 'The Saint in a Scientist'). He also features in a flipbook for kids 'They Made What? They Found What?'. He has been awarded the
country's highest scientific honor - the Shanti Swarup Bhatnagar Prize for his seminal contributions.
2022 AFMSS: Numerical Simulation and Modelling of Turbulent, Plane Poiseuille-Couette Flow
D. I. Pullin
Caltech
4.00pm Wednesday 13 April 2022
Online Event (2022 Australasian Fluid Mechanics Seminar Series)
Numerical simulation and mean-flow modelling of plane Poiseuille-Couette (PPC) flows will be described. These flows exist in a parameter
space
)
with
^{1/2})
,
)
where
are independent Reynolds numbers based on the plate speed
and the volume flow respectively. The data base consists of direct numerical simulation at Re=4,000,6,000,
wall-resolved large-eddy simulation at Re = 10,000, 20,000 and some wall-modeled LES up to Re=10^10. The transition from Couette-dominated
(CD) to Poiseuille-dominated (PD) flow will be discussed. This is defined as the mean skin-friction Reynolds number
on the bottom wall changing sign at
)
.
The mean-flow in the
plane is modelled with combinations of patched classical log-wake profiles. Several variants are constructed in both the CD and PD flow regions.
Model calculations give predictions of
, Re_{\tau,t}(Re,\theta))
(the skin-friction Reynolds number on the top wall) and
)
.
Both model and simulation indicate that, as
is increased at fixed Re
)
increases monotonically. The flow laminarizes as
passes through
and then re-transitions to turbulence.
This is accompanied by attenuation of streamwise roll structures present in pure Couette flow. The modelling enables exploration
of the infinite Re limit.
D. I. Pullin is the Robert H. Goddard Professor of Aeronautics, California Institute of Technology. He completed his PhD at Imperial College.
Current research interests include (1) development of large-eddy simulation for high-Reynolds number wall-bounded turbulent flow, (2)
shock-driven flows in fluids and plasmas, and (3) vortex dynamics.
2022 AFMSS: Flow dynamics of vortex rings colliding with solid boundaries
Daniel T H New
NTU, Singapore
4.00pm Wednesday 06 April 2022
Online Event (2022 Australasian Fluid Mechanics Seminar Series)
Vortex rings colliding with solid boundaries often give rise to highly complex vortex structures and behaviour, due to the resulting
vortex-vortex and vortex-boundary layer interactions. This had intrigued researchers for many years, due to fundamental curiosity over a
seemingly “simple” flow scenario and a strong desire to understand the flow mechanisms underpinning the different collision behaviour
associated with different solid boundaries used. At the same time, such flow scenarios are relevant towards engineering applications that
make use of impinging jets for heat transfer or cold spray purposes. This talk will describe experimental and numerical work conducted on
vortex rings colliding with round cylinders and V-walls, with particular attention paid towards how variations in key geometrical parameters
could produce significantly different collision outcomes. Laser-induced fluorescence, particle image velocimetry and large-eddy simulation
results will be used to showcase these flow differences and how the simulations are able to reproduce the basic resulting vortex structures
and flow behaviour that agree well with the flow models.
Daniel T. H. New graduated from the National University of Singapore (NUS) with a PhD in Mechanical Engineering in 2004 after working on
jet-in-crossflow phenomenon. He was with Temasek Laboratories, NUS (TL@NUS) as an Associate Scientist and later as a Research Scientist in
2004 specializing in flow control, before he ventured into fundamental high-speed combustion research at the University of Texas, Arlington,
USA as a post-doctoral visiting researcher. He was a Lecturer at the University of Liverpool, UK between 2005-2010 and worked on jet-mixing
enhancements, before joining Nanyang Technological University (NTU), Singapore in 2010. He is currently an Associate Professor at the School
of Mechanical and Aerospace Engineering, NTU and his current research interests include experimental fluid dynamics and aerodynamics, vortex
dynamics, flow physics and flow control in general.
2022 AFMSS: Hierarchy of counter-rotating pairs of vortex tubes in turbulence
Susumu Goto
Osaka University
4.00pm Wednesday 30 March 2022
Online Event (2022 Australasian Fluid Mechanics Seminar Series)
Developed turbulence is composed of coherent vortices at various length scales. For example, the below figure shows the scale-decomposed
turbulence (DNS results, Re=5000) behind a cylinder. Here, we use a combination of the Gaussian filters in real space for the scale
decomposition. The large (blue) vortices are the rolls shedding from the cylinder, and they form counter-rotating pairs, which are
accompanied by a straining field around them. These large-scale shears stretch and create smaller vortices (the yellow rib vortices).
The rib vortices also form counter-rotating pairs to stretch and create further smaller (black) vortex tubes in straining fields around
pairs of them. This successive vortex stretching process is the energy cascade in the inertial range, which terminates at the scale
(the scale of the black vortices in this case) when viscous effects get faster than the stretching. In this talk, we show the universality
of this hierarchy of coherent vortices and its role in some transport phenomena by using examples of turbulence in a periodic cube, a
turbulent boundary layer, turbulent channel flow, and solid particle transports in these turbulences.
Susumu Goto is a Professor of fluid mechanics in the Graduate School of Engineering Science at Osaka University. He received PhD in 1999
from the Graduate University for Advanced Studies (supervisor: Prof. Shigeo Kida). He then joined the National Institute for Fusion Science
and he stayed at Imperial College London in 2003-2004, where he worked with Prof. J. Christos Vassilicos. After that, he studied at Kyoto
and Okayama before joining Osaka University in 2012. He is theoretically, numerically, and experimentally studying the science and
engineering applications of various complex flow phenomena.
2022 AFMSS: Model-based design of active and passive flow control for wall turbulence
Mitul Luhar
USC
4.00pm Wednesday 23 March 2022
Online Event (2022 Australasian Fluid Mechanics Seminar Series)
Control of wall-bounded turbulent flows has been an important area of research for several decades. However, the development of effective
control techniques has been hindered by the limited availability of computationally-tractable models that can guide design and optimization.
This talk describes extensions of the resolvent analysis formalism that seek to address this limitation. Under the resolvent formulation,
the turbulent velocity field is expressed as a superposition of propagating modes (‘resolvent modes’), identified via a gain-based
decomposition of the Navier-Stokes equations. Control is introduced into this framework via changes to the boundary conditions or through
additional forcing terms in the governing equations. This alters the structure and gain of resolvent modes, whereby a reduction in gain
indicates turbulence suppression. The modeling framework reproduces observations from previous experiments and simulations for passive
techniques (e.g., riblets, compliant walls) as well as active feedback flow control (e.g., opposition control), and provides useful guidelines
for the development of practicable control techniques.
Mitul Luhar is Associate Professor of Aerospace and Mechanical Engineering at the University of Southern California. Research in his group
tackles control of wall-bounded turbulent flows and fluid-structure interactions; this work combinates laboratory experiments and reduced
complexity modeling. Mitul is the recipient of the National Science Foundation CAREER Award and the Air Force Office of Scientific Research
Young Investigator Award. Prior to joining USC, Mitul was a Postdoctoral Scholar in the Graduate Aerospace Laboratories at Caltech. He earned
his Ph.D. in Civil and Environmental Engineering from MIT in 2012 and B.A. and M.Eng. degrees in Engineering from the University of Cambridge
in 2007.
2022 AFMSS: The Spectral Link in Turbulent Frictional Drag
Pinaki Chakraborty
OIST
4.00pm Wednesday 16 March 2022
Online Event (2022 Australasian Fluid Mechanics Seminar Series)
I will review the spectral link in turbulent frictional drag, the missing link between two aspects of turbulent flows that have been the
subject of extensive, but disjoint, research efforts: the frictional drag experienced by a turbulent flow over a wall and the turbulent
spectrum. The standard theory of turbulent frictional drag, which is based on the pioneering work of Prandtl and von Karman, computes the
frictional drag using an indirect approach and makes no contact with the spectrum. By contrast, the spectral link computes the frictional
drag directly and expresses it as a functional of the turbulent spectrum. To illustrate the applications of the spectral link, I will
obtain an analytical version of the arch-famous Nikuradse's diagram that is in minute qualitative agreement with the distinctive features
in the diagram that have remained elusive to any theoretical elucidation. Thereafter, I will discuss unprecedented experimental
measurements of frictional drag in turbulent soap-film flows over smooth and rough walls, and show how the results render the standard
theory incomplete. This research is pursued in close collaboration with Gustavo Gioia (OIST); other collaborators include Nigel Goldenfeld
(U. Illinois), Walter Goldburg (U. Pittsburgh), and Hamid Kellay (U. Bordeaux).
Pinaki Chakraborty is a Professor at the Okinawa Institute of Science & Technology (OIST), where he directs the Fluid Mechanics Unit.
Using a combination of theory, experiments, and simulations, the Fluid Mechanics Unit works on turbulent flows, geological flows,
atmospheric flows, and granular flows. Prior to joining OIST in 2012, Pinaki was at the University of Illinois at Urbana-Champaign, first
at the Department of Theoretical and Applied Mechanics, where he received his Ph.D. in 2006, and then at the Department of Geology, where
he was a postdoctoral fellow and later a Research Assistant Professor.
2022 AFMSS: Modeling the Fluid Physics of Wind Farms
Richard Stevens
University of Twente
4.00pm Wednesday 02 March 2022
Online Event (2022 Australasian Fluid Mechanics Seminar Series)
The performance of large wind farms depends on the development of turbulent wind turbine wakes and the interaction between these wakes.
Turbulence also plays a crucial role in transporting kinetic energy from the large-scale geostrophic winds in the atmospheric boundary
layer towards heights where wind farms can harvest this energy. High-resolution large-eddy simulations (LES) are ideal for understanding
these flow phenomena. Much has been learned from wind farm simulations, which initially focused on 'idealized' situations. Nowadays, the
community increasingly focuses on modeling more complex situations, such as the effect of complex terrain and different atmospheric stability
conditions. As wind farms become larger, the need to improve their design and develop control strategies to mitigate wake effects increases.
However, due to the large separation of length scales and the number of cases, it is unfeasible to use LES for wind farm design. Therefore,
LES are used to develop computationally more tractable modeling approaches ranging from Reynolds Average Navier Stokes (RANS) models to
analytical modeling approaches. In this presentation, we will give particular attention to the challenges of modeling wind farm dynamics in
large-eddy simulations and emerging challenges to account for the effect of mesoscale flow phenomena in these simulations.
Dr. Richard Stevens is an Associate Professor in the Physics of Fluids group at the University of Twente. He has received an ERC-starting
grant. His research interests include computational fluid dynamics and high-performance computing. His work is focused on the fundamental
understanding of turbulent Rayleigh Benard convection and wind farm fluid mechanics.
2021 AFMSS: Large-Scale Coherent Structures in Turbulent Wakes
Georgios Rigas
Imperial College London
6.00pm Wednesday 1 December 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
This talk will give insight into the dynamics of turbulent wakes generated by canonical three-dimensional bluff-bodies and their control.
Using wind-tunnel measurements (synced PIV and pressure) in the wake of an axisymmetric body at Reynolds number of ~200,000 – well into
the turbulent regime – we will demonstrate that turbulent coherent structures manifest due to spatiotemporal symmetry break occurring at
transitional regimes. Due to ergodicity, these structures restore statistically the broken symmetries at sufficiently high Reynolds numbers,
which prevents their identification at turbulent regimes using existing modal decomposition techniques. A symmetry-aware Proper Orthogonal
Decomposition framework has been developed and implemented based on autoencoders to extract the coherent symmetry-invariant structures.
Finally, recent results for the control of coherent structures for road-vehicle drag-reduction applications will be demonstrated. Nonlinear
dynamic feedback controllers are optimally tuned using a data-driven Reinforcement Learning framework, capable of stabilising the wake and
substantially reducing the mean drag through synthetic jets or flaps placed at the rear trailing edges of the vehicle.
Dr Georgios Rigas is a Lecturer in the Department of Aeronautics at Imperial College London. Before joining IC in 2019, he was a Postdoctoral
Scholar at Caltech and the University of Cambridge. He received his Ph.D. in Aeronautical Engineering from Imperial College in 2015. His
work is focused on the fundamental understanding and control of transitional and turbulent flows.
2021 AFMSS: Stochastic and Statistical Dynamical Models of Geophysical Flows
Terry O'Kane
CSIRO
4.00pm Wednesday 24 November 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
The 2021 Nobel prize in physics, awarded to Manabe, Hasselmann and Parisi, focussed on understanding complexity in physical
systems. In particular, the work of Hasselmann informed the general framework of stochastic models to understand the basic processes
leading to the emergence of multiple length and time scales and the myriad causal interactions that determine climate variability.
In this seminar, I will describe the application of multivariate stochastic models to modelling and predicting seasonal to decadal
climate variability and coherence resonance effects including methods first developed by Hasselmann. Beyond assumptions of statistical
stationarity, more general regularised approaches incorporating optimization and numerical methods from applied mathematics, have been
developed to generate data driven stochastic models whose parameters are time dependent, thereby allowing for the identification of
metastable states in nonstationary flows. Applying concepts from dynamical systems, such as hyperbolicity and local attractor dimension,
these reduced order stochastic models are shown to provide a theoretical basis for the specification of forecast covariances and
selection of initial forecast perturbations in operational weather prediction. Finally, the link between generalised Langevin equations
and statistical closure theories of inhomogeneous turbulence are explored. Throughout, specific applications to problems in climate,
atmospheric and ocean dynamics are described.
Terry O’Kane is principal research scientist and leader of the geophysical fluids team in the climate science centre at CSIRO Oceans
and Atmosphere. Prior to that he was an Australian Research Council Future Fellow and in 2013 was awarded the JH Michell medal of the
Australian Mathematics Society. His work focusses on aspects of nonlinear and stochastic climate dynamics including weather and climate
prediction, data assimilation and statistical mechanics and dynamics.
2021 AFMSS: Underlying Subcritical Chaos and Spiral Turbulence in Taylor-Couette Flow
Alvaro Meseguer
UPC
7.00pm Wednesday 17 November 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
We investigate the local self-sustained process underlying spiral turbulence in counter-rotating Taylor-Couette flow using a
periodic annular domain, shaped as a parallelogram, two of whose sides are aligned with the cylindrical helix described by the
spiral pattern. The primal focus of the study is placed on the emergence of drifting-rotating waves (DRW) that capture, in a
relatively small domain, the main features of coherent structures typically observed in developed turbulence. The transitional
dynamics of the subcritical region, far below the first instability of the laminar circular Couette flow, is determined by the
upper and lower branches of DRW solution originated at saddle-node bifurcations. The mechanism whereby these solutions
self-sustain, and the chaotic dynamics they induce, are conspicuously reminiscent of other subcritical shear flows. Remarkably,
the flow properties of DRW persist even as the Reynolds number is increased beyond the linear stability threshold of the base
flow. From these DRW, two period-doubling cascades of relative periodic orbits emerge, leading to two strange attractors. We
will describe the mechanisms that later on destroy the attractors through boundary crises. These mechanisms are similar to the
ones recently reported in plane-Couette flow.
Alvaro Meseguer is an Associate Professor in the Department of Physics at Universitat Politechnica de Catalunya (UPC). He
received his Ph.D. in Applied Physics from UPC and was an EPSRC Postdoctoral Research Officer at Oxford University. His research
interests involve computational fluid dynamics, transition to turbulence, and dynamical systems theory. (Book recently published:
Fundamentals on Numerical Mathematics for Physicists and Engineers, Wiley 2020).
2021 AFMSS: Mixing-Up the Climate? How the Mystery of Stratified Turbulence is Controlling All Our Futures
Colm-cille Caulfield
University of Cambridge
5.00pm Wednesday 10 November 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Feynman acknowledged that "turbulence is the most important unsolved problem of classical physics”, and it is always important
to remember that he was referring to the simplest case of a fluid of constant density. An even more challenging class of
problems arise when the turbulent fluid has a variable density, as turbulent mixing can then convert injected kinetic energy
into both viscous dissipation and potential energy. Of course, the earth’s oceans are just such variable-density stratified
fluids, and the larger scale effect of such stratified turbulence is one of the key areas of uncertainty in modelling the
global climate system. As human activity strongly perturbs that system’s boundary conditions, it is critical to understand
better how stratified turbulence is born, lives and dies within the world’s oceans. Fortunately, enormous advances in data
availability from both observation and numerical simulation have led to breakthroughs in our fundamental understanding of
turbulence in stratified fluids. In this talk I review some of these recent breakthroughs, and pose some of the fascinating
open questions still requiring answers, highlighting how access to vast quantities of data is both a challenge and an exciting
opportunity for the mathematically-minded (classical) physicist.
Colm-cille P. Caulfield is Professor of Environmental and Industrial Fluid Dynamics at the University of Cambridge, where he
is a member of the BP Institute and the head of the Department of Applied Mathematics and Theoretical Physics. Before taking
up his position in Cambridge in 2005, he also held faculty positions in Environmental Engineering at the University of
California, San Diego, and in Mathematics at the University of Bristol. His research focuses on stability, transition, turbulence
and mixing in environmental and industrial flows, particularly where density differences play a dynamically significant role.
He is an associate editor of the Journal of Fluid Mechanics (Rapids).
2021 AFMSS: Bayesian Inference for Dynamical System Identification from Time-Series Data
Robert Niven
UNSW Canberra
4.00pm Wednesday 3 November 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Many inference problems including those of fluid mechanics involve a dynamical system, usually represented by
)
, where
is a state vector,
is the derivative vector, and
is the system model. Since the time of
Newton, researchers have grappled with the problem of system identification: how should a user accurately and efficiently
identify the model f, including its functional family and parameter values, from time-series data? Historically, a large
assortment of machine learning methods have been used, including linear methods, computational intelligence (data-driven)
methods, supervised or unsupervised learning, order reduction methods and statistical tools. However, few researchers have
applied Bayesian inference, the fundamental method for the discovery of models from data.
This seminar provides a Bayesian perspective on dynamical system identification. Firstly, Bayes’ theorem and its key constructs
are introduced. The Bayesian maximum a posteriori (MAP) method is then applied to time-series data, and shown to be equivalent
to a generalized Tikhonov regularization scheme, providing a rational justification for the choice of the residual and
regularization terms respectively from the likelihood and prior distributions. The Bayesian viewpoint also provides access to
the full Bayesian apparatus, enabling the ranking of models, the quantification of model uncertainties, and the exploration of
the functional form of the posterior. Two Bayesian methods, joint maximum a posteriori (JMAP) and the variational Bayesian
approximation (VBA), are compared to the popular SINDy algorithm for thresholded least-squares regression, by application to
several dynamical systems with added noise. The case studies demonstrate several advantages of the Bayesian framework for model
discovery from time-series data.
Robert Niven is an Associate Professor in the School of Engineering and Information Technology, UNSW Canberra. He conducts
research in (i) probabilistic inference applied to a variety of natural and engineered systems, (ii) theoretical fluid mechanics,
and (iii) environmental contaminant systems. A/Prof. Niven’s research has been recognised by several prestigious ARC and
international grants and fellowships. He is a current Council member of the AFMS, and co-founder and current Chair of its ACT
Chapter.
2021 AFMSS: Interactions between coherent structures in turbulent jets
Petrônio Nogueira
Monash University
6.00pm* Wednesday 27 October 2021 (*Please note change in start time)
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Coherent structures of several kinds have been observed in turbulent jets since the early 70’s. The most well-known is the
Kelvin-Helmholtz (KH) wavepacket, which arises from a linear instability mechanism of the flow and plays a key role in sound
generation. Recently, other energetic coherent structures were shown to exist in the turbulent field, all associated with
different regions of the frequency-wavenumber spectrum. At low frequencies and high azimuthal wavenumbers, streaks arise as
a result of the lift-up effect, where elongated streamwise vortices (or rolls) generate streamwise elongated structures in
axial velocity. At low frequencies and low azimuthal wavenumbers, structures are amplified via the Orr mechanism. Finally, at
zero frequency and zero azimuthal wavenumber, a shock-cell structure may be generated by the pressure mismatch at the nozzle
in imperfectly expanded supersonic jets, which can also be predicted using linear stability tools. The objective of this talk
is to analyse the interaction between some of these structures with the KH mode, which may lead to insight on their effects
on sound generation. To this end, a combination of reduced order models will be applied to both jets and confined shear layers,
which will allow us to understand how the KH instability mechanism is modified by them.
Petrônio Nogueira is a Research Fellow at the Laboratory for Turbulence Research in Aerospace and Combustion (LTRAC), Monash
University. He received his PhD from the Instituto Tecnológico de Aeronáutica (ITA - Brazil) in 2019, during which he spent
six months as a visiting PhD student at the Royal Institute of Technology (KTH - Sweden). Most of his work is focused on the
identification and analysis of the dynamics of coherent structures in turbulent flows, and he has been studying resonance
phenomena and noise generation in shock containing jets since 2020.
2021 AFMSS: Hamiltonian Stability Theory for Fluids and Plasmas
Makoto Hirota
Tohoku University
6.00pm* Wednesday 20 October 2021 (*Please note change in start time)
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Linear stability of inviscid fluids and plasmas is generally discussed from the viewpoint of Hamiltonian dynamical system.
The "canonical variable" for a fluid system is not the Eulerian velocity field, but the Lagrangian fluid particle orbits. In
terms of the infinitesimal displacement field of fluid particles, the linearized dynamical system is reduced to a Newton's
equation of motion including gyroscopic and potential forces (Friemann & Rotenberg 1960).The further reduced system for
isovortical perturbation (Arnold 1966) is obtained under the topological constraint imposed by the vorticity conservation law.
Various sufficient conditions for stability are systematically derived because of this framework. However, these sufficient
conditions cannot achieve necessity in the presence of negative energy modes (which may be continuum mode in fluid system). If
one can either eliminate or invert all negative energy modes successfully, necessary and sufficient condition becomes
available. After reviewing this framework, its application to extended magnetohydrodynamics(or two-fluid plasma) is introduced.
Reference: M. Hirota, Phys. Plasmas 28, 022106 (2021).
Makoto Hirota is an Associate Professor of Institute of Fluid Science, Tohoku University. He received his Ph.D. from The
University of Tokyo and has worked as a postdoctoral fellow at Faculty of Mathematics, Kyushu University and Division of
Advanced Plasma Research, Japan Atomic Energy Agency. He is a theoretical physicist studying hydrodynamic and magnetohydrodynamic
stability problems that occur in boundary layer flows, vortices, magnetically confined plasmas, space plasmas and so on.
2021 AFMSS: On-the-fly Reduced Order Modeling with Time Dependent Bases
Hessam Babaee
University of Pittsburgh
4.00pm Wednesday 13 October 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Many important problems in fluid mechanics are described by high-dimensional partial differential equations (PDEs). The
computational cost of solving these problems using classical discretization techniques increases exponentially with respect to
the number of dimensions –– a fundamental challenge that is dubbed as the curse of dimensionality. On the other hand, many of
these high-dimensional problems have a much lower intrinsic dimensionality, that if discovered, can mitigate the curse of
dimensionality. This calls for techniques that extract and exploit correlated structures directly from the PDE. This approach
is in direct contrast to classical discretization techniques that disregard multi-dimensional correlations and result in
inefficient solutions for high-dimensional problems. While there are numerous data-driven dimension reduction techniques that
can extract these correlated structures by solving the full-dimensional PDE, these techniques are only feasible for
lower-dimensional PDEs (e.g., 2D/3D). This same workflow is impracticable for many high-dimensional PDEs as computing the
solution of the full-dimensional PDE is the very problem we cannot afford to solve. To this end, we present a reduced order
modeling framework, in which the correlated structures are extracted directly from the PDE –– bypassing the need to generate
data. These structures are exploited by building on-the-fly reduced order models (ROM). The correlated structures are
represented by a set of time-dependent orthonormal bases and their evolution is prescribed by the physics of the problem. We
present several demonstration cases including reduced order modeling of reactive species transport equation in turbulent
combustion as well as sensitivity analysis and uncertainty quantification in fluid dynamics problems.
Hessam Babaee is currently an Assistant Professor in the Department of Mechanical engineering and Materials Science at the
University of Pittsburgh. He earned his PhD in Mechanical Engineering and Masters in Applied Mathematics both from Louisiana
State University in 2013. He then joined the Mechanical Engineering Department at MIT for his postdoctoral research, where he
worked with Prof. George Karniadakis. He then joined the University of Pittsburgh in January 2017. His research is focused on
developing reduced order model and machine learning techniques for fluid mechanics problems. His research has been funded by
many organizations including NASA, National Science Foundation (NSF), National Institute of Health (NIH) and Air Force Office
of Scientific Research (AFOSR).
2021 AFMSS: Mean and turbulent characteristics of a bottom boundary layer forced by a strong surface tide and large amplitude internal waves
Nicole Jones
University of Western Australia
4.00pm Wednesday 06 October 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
The bottom boundary layer [BBL] is the region where the flow is directly influenced by the presence of the seabed. Despite
the BBL often being thin with respect to the total ocean depth, the dynamics of this layer are of great physical, biological
and engineering importance. I will present 15-days of detailed observations of a near well-mixed bottom boundary layer at a
250 m deep continental shelf site, where the ocean flow was characterised by strong tides and large internal waves. The boundary
layer thickness varied at tidal frequencies, and was 10 m thick on average. In the lowermost 1 m of this layer, the flow
conformed to conventional boundary layer. More than 1 m above the bed, however, the overlying internal waves modified both the
nature of the turbulent flow and the time-averaged properties of the bottom mixing-layer. While the instantaneous BBL thickness
is dominated by internal wave pumping, the strength of the ambient stratification and the frequency of the oscillation are
important controls on the time averaged boundary-layer thickness.
Associate Professor Nicole Jones is a Physical Oceanographer at the University of Western Australia. She uses a combination
of field observations and numerical modelling to study primarily relatively small-scale ocean dynamics, including turbulent
mixing, internal waves and ocean eddies. Under-standing these processes is vital to quantify the transport of heat, pollutants
and nutrients around the ocean. Nicole has extensive fieldwork and cruise experience and a particular interest in the development
of novel field-observation techniques. Nicole has been an Editor for the Journal of Physical Oceanography since 2018. She
represents the Western Australian marine science community by leading the Western Australia node of Australia’s Integrated Marine
Observing System (IMOS). Since 2019 Nicole has served on the Research Advisory Committee of the Marine National Facility.
2021 AFMSS: Impact of surface and free-stream disturbances on boundary-layer transition
Xuesong Wu
Imperial College London
5.00pm* Wednesday 29 September 2021 (*Please note change in start time)
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Laminar-turbulent transition in boundary layer flows depends crucially on external perturbations that are present on the
surface and in the free stream. Depending on their physical nature as well as locations and scales, these perturbations may
influence transition route and position via different physical mechanisms including the familiar ones of receptivity,
alteration of linear instability and the newly identified local scattering process. Establishing physics-based quantitative
relations between the transition location and external perturbations is considered to be the ultimate aim of transition
research. In this talk, I will report some of recent efforts made to achieve that goal. These include a particularly strong
receptivity of supersonic boundary layers to free-stream sound waves in a small range of incident angle, a local scattering
theory quantifying the impact of abrupt changes on instability, and a complete initial-boundary-value problem describing
Gortler vortices induced by high-level free-stream vortical disturbances. The respective importance of theoretical concepts,
mathematical analyses and full numerical computations in these efforts will be highlighted.
Professor Xuesong Wu is a Professor of Applied Mathematics in the Faculty of Natural Sciences, Department of Mathematics at
Imperial College London.
2021 AFMSS: What can point-particle simulations tell us about turbulent dispersed flows?
Cristian Marchioli
University of Udine
4.00pm Wednesday 22 September 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Particle transport and mixing in turbulent flows are fundamental to science as well as to technology. Examples of
open scientific issues include emissions reduction in combustion, rheological characterization of fibrous particle
suspension, plankton population dynamics, convection of pollutants in the atmosphere, to name a few. The simplest
numerical framework to study the dynamical and statistical features of turbulent particle dispersion is based on
the assumption that particles can be modeled as point-like spheres brought about by the flow. In spite of its simplicity,
this framework has led to significant advancements in the study of particles-turbulence interactions, allowing the precise
identification of the coherent structures responsible for particle sedimentation and re-entrainment in turbulent boundary
layers. In this talk we examine a possible source of bias in particle dispersion, which arises when particles are
non-spherical (elongated), showing how this affects particle motion, preferential concentration and accumulation in
turbulent boundary layer. We also discuss the possibility of using the point-particle approach to examine from a
fundamental perspective particle interaction with a fluid interface, a problem of practical importance for scrubbing
processes.
Cristian Marchioli is Associate Professor of Fluid Mechanics at the University of Udine, Editor of Acta Mechanica and
former chairman of the COST Action “Fiber suspension flow modeling”. Currently, Prof. Marchioli is the Coordinator of
the MSCA ITN Network COMETE “Next-Generation Computational Methods for Enhanced Multiphase Flow Processes” and sits in
the scientific council of the International Center of Mechanical Sciences, where he coordinated several advanced schools
on particles in turbulence. His research interests involve multiphase flow modeling, from small-scale particle-turbulence
interactions to large-scale modeling of gas-solid/gas-liquid flows. Prof. Marchioli has published 60+ papers and 150+
conference proceedings. He has also delivered several invited and keynote lectures at international conferences.
2021 AFMSS: Active control of flow-induced vibration of a circular cylinder
Jisheng Zhao
Monash University
4.00pm Wednesday 15 September 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Flow-induced vibration (FIV) of structures is an important problem seen a large variety of engineering applications,
e.g., from high-rise buildings in winds to offshore oil platforms and rigs and to energy-harvesting foils. In order
to gain a deeper understanding of the fundamental characteristics and control of FIV, the present study experimentally
investigated the FIVs of a rotating circular cylinder that was allowed to oscillate with one degree of freedom in the
cross-flow direction. It was found that the imposed body rotation could significantly enhance and attenuate the cylinder
vibration in a parameter space of the rotation rate and flow velocity. Moreover, we assessed the fluid-flow energy
harvesting performance from FIV of rotating cylinder.
Jisheng Zhao is a Research Fellow (ARC DECRA Fellow) in the Department of Mechanical and Aerospace Engineering. He
obtained his PhD degree from Monash University in 2012. His main research interests include fluid-structure interactions,
flow-induced vibration of bluff bodies, structural vibration control, fluid-flow energy harvesting, and aerodynamics of
flapping wings.
2021 AFMSS: Tracking streaks in the buffer layer of wall-bounded turbulence
Jane Bae
Caltech
4.00pm Wednesday 08 September 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Among the many organized structures observed in near-wall turbulent flows, streaks, defined as regions of slowly
moving fluid elongated in the direction of the mean flow, are considered to be of major importance for their role
in the regeneration of turbulent energy. Here, we identify and track individual streaks in time using time-resolved
direct numerical simulation data of a low Reynolds number channel flow. The analysis of the streaks shows that there
is a clear distinction between wall-attached and detached streaks, and that the former can be further categorized
into streaks that are contained in the buffer layer and the ones that reach the outer region. The results reveal that
streaks are born in the buffer layer, coalescing with each other to create larger streaks that are still attached to
the wall. These large tall-attached streaks eventually split into wall-attached and wall-detached components, which
are strongly related to ejections or burst events.
Jane Bae is an Assistant Professor in Aerospace at the Graduate Aerospace Laboratories at Caltech. She received her
Ph.D. in Computational and Mathematical Engineering from Stanford University in 2018. She was a postdoctoral fellow
in the Graduate Aerospace Laboratories at Caltech and the Institute for Applied Computational Science at Harvard
University before joining the Caltech faculty. Her main research focuses on computational fluid mechanics, in
particular on modeling and control of wall-bounded turbulence.
2021 AFMSS: Developments and Capabilities Of Lattice Boltzmann Method For non-Ideal Fluid Flows and Mixtures
Emilie Sauret
Queensland University of Technology
4.00pm Wednesday 01 September 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Non-ideal fluid flows and mixtures are ubiquitous in many engineering applications, from renewable thermodynamic
cycles to lab-on-a-chip devices. Those fluids and mixtures exhibit significant inter and intra molecular
interactions that affect their macroscopic behaviour. This talk will present the development and application of
a high-order multi-component Lattice Boltzmann (LB) model. Expanding LB models to higher orders makes it possible
to solve nonequilibrium flow quantities and fully recover the Navier-Stokes solution. Challenges in developing,
validating and applying such high-order multi-component models will be discussed. The presented approach is a step
towards an efficient, robust and accurate numerical method for simulating non-ideal fluid flows and mixtures and
understanding complex physical phenomena.
Dr. Emilie Sauret is a Professor in the School of Mechanical, Medical and Process Engineering, Queensland University
of Technology, and an elected council member of the Australasian Fluid Mechanics Society. She received a PhD in
Turbulence Modelling from Pierre & Marie Curie University, Paris, France in 2004. Following some time in industry,
she was awarded an ARC-DECRA in 2013 and a Future Fellowship in 2020. Dr. Sauret has extensive interdisciplinary
research experience at the crossroads between mechanical engineering, applied mathematics, and applied physics. She
specialised in developing advanced computational models to understand complex fluid phenomena for a variety of
engineering applications.
2021 AFMSS: Measurements in Wall-Bounded Turbulence
Alexander J. Smits
Princeton University
9.00pm* Wednesday 18 August 2021 (*Please note change in start time)
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Our understanding of turbulent boundary layer scaling and structure has advanced greatly in the past 20
to 30 years. On the computational side, direct numerical simulations and large-eddy simulations have
made extraordinary contributions as numerical methods and computational resources have advanced, while on
the experimental side major advances in instrumentation have made available new imaging and quantitative
techniques that provide unprecedented accuracy and detail. Here, I illustrate how our progress has been
aided by the development of such experimental methods by reference to three questions on the scaling of
turbulent boundary layers: (1) the similarity behavior in supersonic and hypersonic flows; (2) the structure
of the outer layer in subsonic flows at high Reynolds number; and (3) the scaling of the turbulent stresses
in the near-wall region.
Alexander J. Smits is the Eugene Higgins Professor Emeritus of Mechanical and Aerospace Engineering at
Princeton University. His research interests are centered on fundamental, experimental research in turbulence
and fluid mechanics. He has authored or co-authored three books and more than 450 journal and conference
papers. In 2004, Dr. Smits received the American Institute of Aeronautics and Astronautics (AIAA) Fluid
Dynamics Award. In 2007, he was awarded the American Society of Mechanical Engineers (ASME) Fluids Engineering
Award, and in 2011 he received a degree Honoris Causa (D.Eng.) from the University of Melbourne; in 2014, he
received the AIAA Aerodynamic Measurement Technology Award, and in 2019 he was awarded the Fluid Dynamics Prize
of the American Physical Society (APS). In 2020, he received the George K. Batchelor Prize in Fluid Mechanics
from the International Union of Theoretical and Applied Mechanics. He is a Member of the National Academy of
Engineering and the American Academy of Arts and Sciences, and a Fellow of APS, AIAA, ASME, the American
Association for the Advancement of Science, and the Australasian Fluid Mechanics Society. He served as the
Editor-in-Chief of the AIAA Journal from 2015 to 2021.
2021 AFMSS: Seeing in the dark
Tamer A. Zaki
Johns Hopkins University
9.00pm* Wednesday 11 August 2021 (*Please note change in start time)
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Numerical simulations of turbulence provide non-intrusive access to flow quantities of interest, although
they often invoke simplifying assumptions that can compromise realism such as truncated computational
domains and idealized boundary conditions. Experiments, on the other hand, probe the true flow with less
assumptions, but must nonetheless contend with limitations that arise due to sensor technology such as
the tradeoff between field of view and spatio-temporal resolution. Assimilating observations directly in
simulations can combine the advantages of both approaches and mitigate their respective deficiencies. The
problem is expressed in variational form, where we seek the flow field that satisfies the Navier-Stokes
equations and optimally reproduces available data. In this framework, observations are no longer a mere
record of the instantaneous, local quantity, but rather an encoding of the antecedent flow events that we
aim to decode using the governing equations. Chaos plays a central role in obfuscating the interpretation
of the data: observations that are infinitesimally close may be due to entirely different earlier conditions.
We will examine a number of state estimation problems that expose important aspects of wall turbulence and
the fundamental difficulties of reconstructing the full state from limited observations.
Tamer Zaki is a professor in the Department of Mechanical Engineering at Johns Hopkins University (JHU).
His research interests span high-fidelity simulations for the prediction of transitional and turbulent shear
flows, in both Newtonian and complex fluids, and the development of nonlinear optimization techniques for
data assimilation, interpretation of flow measurements and optimal sensing. Zaki has garnered several
recognitions including the Office of Naval Research Young Investigator Award and the William H. Huggins
Excellence in Teaching Award. He is member of the JHU Center for Environmental & Applied Fluid Mechanics,
the Institute for Data Intensive Engineering & Science, and the American Physical Society. He serves on
the Editorial Advisory Board of Flow, Turbulence and Combustion and the Editorial Board of Physical Review
Fluids.
2021 AFMSS: Geometrical Aspects Of Biological Locomotion At Low Reynolds Number
Kenta Ishimoto
Kyoto University
4.00pm Wednesday 04 August 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Microorganisms live at low Reynolds number, where the steady Stokes equations well describe the biological
fluid phenomena. In this talk, after an introduction to the hydrodynamics of swimming microorganisms, a
couple of geometrical topics in the theory of microswimming will be presented. In particular, I will talk
about a general theory of the hydrodynamic shape of a microscopic object, deriving a new formula for the
motion of chiral particles with applications to biased locomotion of bacteria in a fluid flow. If time
permits, I will discuss a control problem of microscopic particles using a geometrical theory.
Dr Kenta Ishimoto is an Associate Professor at Research Institute for Mathematical Sciences, Kyoto
University. He received a PhD in Mathematical Science from Kyoto University in 2015, followed by research
experiences at Kyoto University, University of Oxford and The University of Tokyo, before joining as a
faculty at Kyoto University in 2019. He mainly studies biofluid mechanics at the cellular scale and
related applied mathematics.
2021 AFMSS: Let's get high (order)!
Esteban Ferrer
ETSIAE-UPM - School of Aeronautics
4.00pm Wednesday 30 June 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
High order methods (order ≥ 2) have seen a rise in popularity during the last 10 years and are today
relatively mature. They are characterised by low numerical errors and by their ability to perform mesh
refinement and/or polynomial enrichment to achieve accurate solutions. Today, they are sufficiently
mature to cover a wide range of applications and flow regimes. However, to industrialise these methods,
robustness, physical model complexity and computational efficiency still need to be improved. In this
talk, we present our last developments in high order methods that include solving a wide range of flow
regimes/physics: compressible, incompressible, turbulent (LES) and multiphase flows (Navier-Stokes with
Cahn-Hilliard). In addition, we will cover methods to improve stability (e.g. stable energy schemes)
and new immersed boundary methods to facilitate meshing. Finally, we focus on the efficiency of high
order solvers and discuss local p-adaption, implicit time-stepping and multigrid. Examples will include
aeronautical applications, wind turbines, acoustics and stability/sensitivity analyses for flow
control.
Dr. Esteban Ferrer is Associate Professor in Applied Mathematics at the School of Aeronautics ETSIAE-UPM
(Madrid). He received his PhD from the University of Oxford and was awarded two Masters Degrees in
Mechanical Engineering ETSEIB-UPC (Barcelona) and in Aeronautical Engineering from ISAE (Toulouse).
Esteban worked in industry before becoming an academic and has more than 18 years’ experience in the
fields of numerical simulation and stability analysis. His current research focusses in developing high
order solvers and flow control techniques for wind turbines and aeronautical applications.
2021 AFMSS: Instabilities and coherent structures in swirling flows and their relevance for thermoacoustics
Kilian Oberleithner
Technische Universität Berlin
4.00pm Wednesday 23 June 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Swirling flows feature a remarkable richness in flow instabilities such as centrifugal instabilities,
inertial waves and global helical modes. Likewise, swirling flows and their instabilities are of high
technical relevance and need to be understood and controlled. E.g., swirling flows play a key role in
stabilizing turbulent flames in modern lean-premixed combustion systems, they occur in hydro turbines
where their instabilities cause severe pressure oscillations, and they contribute to the wake recovery
of wind turbines. In this talk, we briefly review the main characteristics of swirling flows and their
instabilities. We introduce the methodology of linear stability theory for turbulent flows and our
approach to model coherent structures. We then dive into the field of lean-premixed combustion and discuss
recent research on prediction and control of hydrodynamic instabilities in swirl flames and their interplay
with combustion instabilities. We will put a focus on high-Reynolds-number, fully turbulent flows at
industry relevant scales, but we will also make detours to DNS based fundamental studies.
Kilian Oberleithner is a Professor at the TU Berlin and head of the Laboratory for Flow Instabilities
and Dynamics. He completed his PhD in 2012 under the joint supervision of Prof. Oliver Paschereit (TUB)
and Prof. Israel Wygnanski (University of Arizona). He continued research as a post-doc in Prof. Julio
Soria's group in Melbourne, Australia. After his return to Berlin in 2014 he established his own
research group and was appointed as a Junior professor in 2018. His main research interests are focused
on exploring physical mechanisms and developing flow control techniques for reacting and non-reacting
turbulent shear flows, using linear stability theory and data-driven low-order modelling with the aim of
bridging fundamental and applied research.
2021 AFMSS: Small-scale turbulence phenomenon: could have we got it wrong?
Lyazid Djenidi
The University of Newcastle
4.00pm Wednesday 16 June 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
At the 1961 International Colloquium on Turbulence, held in Marseille (France), Kolmogorov presented
his response to Landau’s remark which states that the large-scale and slow variations of the energy
dissipation prevent the universality of small-scale turbulence. The theory presented, which has been
reproduced in a 1962 Journal of fluid Mechanics article (JFM 13, 82-85) and commonly known as K62,
shaped the current dominant understanding of the behaviour of small-scale turbulence. However, among
this consensus, are growing “dissident voices” (among which the present speaker) who do not share the
view that K62 describes the correct behaviour of small-scale turbulence at very large, if not infinite,
Reynolds number. In this seminar we will briefly highlight the major issues/inconsistencies raised from
the past and present results and attempt to address these issues by examining the behaviour of the
second order-moment of the velocity increments, S2, obtained via (i) a closed form of the Karman-Howarth
equation and (ii) the 3D energy spectrum.
Lyazid Djenidi is Professor at the College of Engineering, Science and Environment (Mech. Eng Discipline)
at the University of Newcastle (Australia). He completed his PhD (Fluid mechanics) at the Institute de
Mechanique Statistique de la Turbulence (IMST, Marseille, France), the institute where (what an irony of
fate) Kolmogorov presented his K62 theory. After completing his PhD studies, in 1989, he went to
Cambridge University (UK) for a post-doctoral position, before joining the turbulence group at the
University of Newcastle in 1991. His interest in turbulence encompasses experimental, numerical and
theoretical work on turbulent boundary layers, turbulent channel flows, jet and wake flows and
small-scale turbulence.
2021 AFMSS: Simulating urban flows and air pollution in the lab
Christina Vanderwel
University of Southampton
6.00pm* Wednesday 09 June 2021 (*Please note change in start time)
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
The aerodynamics around buildings and within cities are crucial for determining how urban air
pollution spreads. This talk will discuss current approaches to urban flow modelling and the gap in
knowledge when dealing with local scale phenomena. Two experimental cases studies are considered:
a scale model of a Beijing neighbourhood and multi-scale `fractal’ city models. Wind tunnel and
water flume experiments are conducted measuring the drag, velocity, and concentration fields around
the models using a force balance, particle image velocimetry (PIV), and planar laser-induced
fluorescence (PLIF), respectively. Rough-wall boundary layer estimates based on assumptions of
homogeneous surface morphology predict the general trends of the results; however, particular
building arrangements and the presence of tall buildings appear to have distinct local effects on
the flow structure and resulting scalar transport, highlighting the challenges for urban air quality
modelling.
Christina Vanderwel is an Associate Professor in the Aerodynamics and Astronautics Department at the
University of Southampton. She completed her PhD in Mechanical Engineering at the University of Ottawa,
Canada, in 2014. She specialises in experimental fluid mechanics and turbulence, using laser-based
diagnostics and wind tunnels to study the mechanisms of mixing in turbulent flows. She currently holds
a UKRI Future Leaders Fellowship applying her research to study urban wind patterns and how air
pollution spreads in cities.
2021 AFMSS: New perspectives on instability and transition of laminar separation bubbles
Daniel Rodríguez
Universidad Politécnica de Madrid
5.00pm* Wednesday 02 June 2021 (*Please note change in start time)
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Decades of research have established the ubiquity of inflectional instability in laminar separation
bubbles (LSBs) and its dominant role in the laminar-turbulent transition process. However, this
instability alone cannot explain the plethora of different dynamics that are observed, including
three-dimensionalization of the mean flow and self-excited vortex shedding and transition. To fill
these gaps, global instability mechanisms of LSBs were proposed in the past. Partial confirmation of
these mechanisms has been realized experimentally, but most low-turbulence wind tunnel experiments
either did not find evidence of their presence, or attributed possible evidences to consequences of
the inflectional instability alone. This talk will depart from the theoretically-predicted, 3D
global instability of LSBs, that distorts the separated flow along the spanwise direction. New results
for non-linear and secondary instabilities of 3D separated flows will be presented. They show that
the spanwise distortion strongly enhances inflectional instability, potentially leading to their
absolute instability and to the appearance of a self-excited global oscillator. This sequence triggers
the laminar–turbulent transition without requiring external disturbances or actuation. The resulting
LSBs are in good agreement with those reported for low-turbulence wind-tunnel experiments without
explicit forcing. This indicates that the inherent dynamics described by the self-excited instability
can have been present and disregarded in many experimental works.
Daniel Rodríguez is associate professor at the School of Aeronautics of Universidad Politécnica de
Madrid (UPM). After completing his Aerospace Engineering (2007) and Ph.D. (2010) at UPM, he held a
postdoctoral position at Caltech. He was awarded the EU's Marie Curie fellowship (2011-2014) and the
Brazilian's "Attraction of Young Talent" fellowship (2014-2016), during which he was appointed at UPM,
Universidade de Sao Paulo and PUC-Rio, Brazil. From 2016 to 2019 he held a faculty position at UFF,
Brazil. In 2018 he received the "Young Researcher of Rio de Janeiro State" award, and in 2020 he was
appointed as "Echegaray Professor", within the Program of Academic Excellence of the government of the
Community of Madrid.
2021 AFMSS: A computational "rheometer" for turbulent flows
Ali Mani
Stanford University
4.00pm Wednesday 26 May 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
This study presents a numerical procedure, which we call the macroscopic forcing method (MFM),
which reveals the differential operators acting upon the mean fields of quantities transported
by underlying fluctuating flows. Specifically, MFM can reveal differential operators associated
with turbulent transport of scalars and momentum. We present this methodology by considering
canonical problems with increasing complexity. For spatially homogeneous and statistically
stationary systems, we observe that eddy diffusivity can be approximated by an operator of the
form D/√(1-l^2 ∇^2 ), where l is a length scale on the order of large-eddy size and D is a
coefficient. A validation test shows that this operator leads to significant improvement in RANS
prediction of axisymmetric turbulent jets. We show a cost-effective generalization of MFM for
analysis of non-homogeneous and wall-bounded flows, where eddy diffusivity is found to be a
convolution acting on the macroscopic gradient of transported quantities. We introduce MFM as an
effective tool for quantitative understanding of non-Boussinesq effects in turbulence,
particularly, the effects associated with anisotropy and non-locality of macroscopic mixing.
Ali Mani is an associate professor of Mechanical Engineering at Stanford University. He is a
faculty affiliate of the Center for Turbulence Research and a member of Institute for Computational
and Mathematical Engineering at Stanford. He received his PhD in Mechanical Engineering from
Stanford in 2009. Prior to joining the faculty in 2011, he was a senior postdoctoral associate at
Massachusetts Institute of Technology in the Department of Chemical Engineering. His research group
builds and utilizes large-scale high-fidelity numerical simulations, as well as methods of applied
mathematics, to develop quantitative understanding of transport processes that involve strong coupling
with fluid flow and commonly involve turbulence or chaos. His teaching includes the undergraduate
engineering math classes and graduate courses on fluid mechanics and numerical analysis. He is the
recipient of an Office of Naval Research Young Investigator Award (2015), NSF Career Award (2016),
and Tau Beta Pi Teaching Honor Roll (2019).
2021 AFMSS: Ubiquitous free surface flows: from kitchen to volcanoes
Mathieu Sellier
University of Canterbury
4.00pm Wednesday 19 May 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Many flows encountered in our daily lives involve a moving boundary. The shape of a raindrop,
for example, evolves as it falls through the air. Likewise, the free surface of a river deforms
as it encounters obstacles. While the mathematical ingredients required to describe such flows
have been known since the late 19th century and are encapsulated in the Navier-Stokes equations,
solving complex flows with a moving boundary or interface still poses significant challenges and
provides stimulating cross-disciplinary research opportunities. The question at the centre of the
research I will present is “if information about the evolution of a moving interface is available,
can we indirectly infer unknown properties of the flow?” Such a question falls in the realm of
inverse problems for which one knows the effect but is looking for the cause. Specifically, I will
talk about how it is possible to estimate the fluid properties of lava just by looking at how it
flows or what is the best way to rotate a pan to cook the perfect crêpe.
Since 2018, Mathieu Sellier is Professor of Fluid Mechanics in the Department of Mechanical
Engineering at the University of Canterbury (New Zealand). He is also Head of that Department since
2019. Prof Sellier graduated with a Master in “Modelling and Simulation in Mechanics” from Université
Grenoble Alpes (France) in 2000, then got his PhD from the University of Leeds (UK) in 2003 working
on the development of numerical methods to better understand the flow of thin liquid films and droplets
on complex textured surfaces for coating applications. From 2003 to 2006, he was a PostDoc at the
Fraunhofer Institute for Industrial Mathematics (Kaiserslautern, Germany) in the Marie-Curie Research
Training Network MAGICAL (Mathematics for the Glass Industry Computations and Analysis). Prof Sellier
started at the University of Canterbury as a lecturer in Theoretical Fluid Mechanics in 2006 and now
leads the Interfaces and Inverse Problems lab (I&IP). His research interests are broad but typically
revolve around modelling free surface or multiphase flow phenomena at small scales for which capillary
and wetting phenomena dominate (droplets and thin film flows) or at large geophysical scales (river or
glacier flows). Prof Sellier’s other area of research expertise is related to inverse problems for
which one tries to infer the unknown causes of observed phenomena.
2021 AFMSS: From transition to turbulence control
Björn Hof
IST Austria
5.00pm* Wednesday 12 May 2021 (*Please note change in start time)
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
In many shear flows turbulence arises despite the linear stability of the laminar flow and this
transition has remained unresolved for over a century. In this talk I will report recent progress
in experiments and show that the onset of sustained turbulence in pipe and Couette flow corresponds
to a directed percolation phase transition. Moreover, I will show how properties of transitional
flows can be exploited to control turbulence and in particular to fully relaminarize pipe flow at
much higher Reynolds numbers.
Björn Hof is a professor of Physics at the Institute of Science and Technology Austria. Previously
he was a Max Planck Research Group leader at the MPI Göttingen and a lecturer and RCUK fellow at
the University of Manchester. He held postdoctoral positions at the TU Delft and at the University
of Manchester. He obtained his PhD in physics from the University of Manchester. His current work
ranges from studies of the transition to turbulence, to polymer drag reduction, turbulence control,
cardiovascular flows and epidemic modelling. He is a fellow of the American Physical Society.
2021 AFMSS: Universality in the subcritical route to turbulence
Dwight Barkley
University of Warwick
5.00pm* Wednesday 5 May 2021 (*Please note change in start time)
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Recent years have witnessed a profound change in our understanding of the route to turbulence in
wall-bounded shear flows. In stark contrast to the classical Hopf-Landau picture where turbulence
arises through an increase in the temporal complexity of fluid motion, the route to turbulence in
subcritical shear flows occurs via spatio-temporal intermittency and falls in the class of
non-equilibrium statistical phase transitions known as directed percolation. I will review important
results in the field with focus on the spatio-temporal nature of the problem and how universality
manifests itself. I will then describe recent work aimed at capturing the rare events dictating
critical phenomena in wall-bounded transition.
Dwight Barkley is a professor of Mathematics at the University of Warwick. He held postdoctoral
positions at Caltech, Princeton, and ENS Lyon. He obtained his PhD in Physics from the University of
Texas at Austin. His research lies at the interface between high-performance computation, pattern
formation and nonlinear phenomena. He has studied instabilities, waves and patterns in fluid, chemical
and biological systems. His current work focuses on Euler singularities and the onset of turbulence.
In 2005 he was awarded the SIAM J.D. Crawford Prize. He is a Fellow of the American Physical Society
and of SIAM.
2021 AFMSS: Hidden physics models
Maziar Raissi
University of Colorado
4.00pm Wednesday 28 April 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
A grand challenge with great opportunities is to develop a coherent framework that enables blending
conservation laws, physical principles, and/or phenomenological behaviors expressed by differential
equations with the vast data sets available in many fields of engineering, science, and technology.
At the intersection of probabilistic machine learning, deep learning, and scientific computations,
this work is pursuing the overall vision to establish promising new directions for harnessing the
long-standing developments of classical methods in applied mathematics and mathematical physics to
design learning machines with the ability to operate in complex domains without requiring large
quantities of data. To materialize this vision, this work is exploring two complementary directions:
(1) designing data-efficient learning machines capable of leveraging the underlying laws of physics,
expressed by time dependent and non-linear differential equations, to extract patterns from
high-dimensional data generated from experiments, and (2) designing novel numerical algorithms that
can seamlessly blend equations and noisy multi-fidelity data, infer latent quantities of interest
(e.g., the solution to a differential equation), and naturally quantify uncertainty in computations.
I am currently an Assistant Professor of Applied Mathematics at the University of Colorado Boulder.
I received my Ph.D. in Applied Mathematics & Statistics, and Scientific Computations from University
of Maryland College Park. I then moved to Brown University to carry out my postdoctoral research in
the Division of Applied Mathematics. I then worked at NVIDIA in Silicon Valley for a little more than
one year as a Senior Software Engineer before moving to Boulder. My expertise lies at the intersection
of Probabilistic Machine Learning, Deep Learning, and Data Driven Scientific Computing. In particular,
I have been actively involved in the design of learning machines that leverage the underlying physical
laws and/or governing equations to extract patterns from high-dimensional data generated from
experiments.
2021 AFMSS: Gravity currents in heterogeneous porous media
Edward Hinton
University of Melbourne
4.00pm Wednesday 21 April 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Many analytical results have been obtained for gravity-driven flow in uniform porous media, which
provide checks on numerical methods and furnish insight into the underlying physical processes.
However, subsurface porous rocks are typically highly heterogeneous, which strongly influences the
flow. In this talk, I examine the effect of some simple heterogeneities on the classical solutions
for flow in porous media and relate the results to applications in CO2 sequestration. First, the
interaction of free-surface flow with a cylindrical inclusion of different permeability is explored.
The flow thickness and streamlines are obtained through simple flux-balance arguments in various
regimes for the relative inclusion width and permeability. Second, I will discuss displacement flow
in a confined layer with a vertical gradient of permeability and analyse how gravity and
permeability variations compete to drive the flow and control the interface evolution.
Edward Hinton is a Harcourt-Doig research fellow at the University of Melbourne
(https://blogs.unimelb.edu.au/edward-hinton/). He previously held a London Mathematical Society
research fellowship at The University of Bristol, UK and prior to that completed his PhD at the
University of Cambridge, UK. His PhD thesis investigated various low Reynolds number environmental
flows. Edward’s research aims to deploy low order models to capture the dominant aspects of a
particular problem and then use numerical methods, laboratory experiments and mathematical
techniques to provide insights into the underlying physical behaviour.
2021 AFMSS: Surface wave control of bacterial biofilms
Hua Xia
Australian National University
4.00pm Wednesday 14 April 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Faraday waves have been shown to produce a rich array of phenomena, from pattern formation,
order to disorder transition, to the generation of two-dimensional turbulent flows [Shats, Phys.
Rev. Lett., 2012; Xia, Phys. Rev. Lett., 2012; Francois, Phys. Rev. Letters, 2013, Xia, Nature
comm. 2013]. The Faraday wave driven surface flows influence turbulent mixing, transport of
inertial particles [Xia, J. Fluid. Mech., 2018; Yang, Phys. Fluids, 2019] and can be utilized to
design turbulence-driven rotors [Francois, Phys. Rev. Fluids, 2018; Francois, Phys. Rev. Lett.,
2020] and self-propelled surface vehicles [Yang, Phys. Rev. Fluids, 2019].
Wave-assisted technology has great potential in engineering of new biomaterials based on bacterial
biofilms. Bacterial biofilm is the most abundant form of life on Earth. The understanding and control
of the biofilm formation has been a research focus for the past 20 years mainly due to its roles in
biofouling of industrial pipelines, antibiotic resistance, and in chronic infections. On the other
hand, industrial wastewater treatment plants and agricultural technologies utilise the benefits of
biofilms. The search for new sustainable technologies has led to the fast development of non-conventional
materials produced by certain bacteria, such as bacterial cellulose.
Understanding environmental factors affecting the attachment and the early stages of the biofilm
development is the key to promoting and discouraging the biofilm growth. We show that surface wave driven
flow can be used to control the formation of the biofilm formation at the liquid solid interface
[Hong, Science Advances, 2020]. By controlling the wavelength, amplitude, and horizontal mobility of the
waves, one can shape the biofilm, and either enhance the growth, or discourage the formation of the biofilm.
Wave driven flows are the strongest at the liquid-air interface, which makes a good candidate for the
control of biofilm formed at the liquid-air interface. We apply this approach to engineer biofilms whose
morphology is controlled by the wave-driven flows. This allows to create different biofilm forms, such as
for example spherical beads, or planar pellicles which are used in many industrial, scientific and
agricultural applications.
Dr Hua Xia has been working at the ANU since 2006 on physics of fluids and their applications in
atmospheric, oceanic and biological systems. Her research has attracted funding from the ARC including
several Discovery projects, a DECRA award (2012-2014) and a Future Fellowship (2015-2019). Dr Xia's current
research focus is on the physics approaches to microbiological systems for novel biophysical applications.
The work presented here is part of her ARC DP19 project 'Transport control in multi-species fluid
suspensions for biomedical applications' (2019-2022).
2021 AFMSS: Controlling and Modelling Transport Phenomena using Surface Engineering
Shervin Bagheri
Royal Institute of Technology (KTH)
4.00pm Wednesday 7 April 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Engineered surfaces with texture, chemical contrasts, pores, and compliance may significantly
modify transport pro-cesses. In this talk, I give a few examples of our work focusing on how
complex surfaces and flowing fluids interact at different length scales. We demonstrate; (i)
how very small changes in either surface texture or chemistry modify lubrication forces, resulting
in non-trivial trajectories of particles traveling parallel to surfaces; ii) how liquid-infused
surfaces modify turbulent friction drag, in particular, when capillary waves develop on trapped
lubricant; iii) how to accurately model transport processes between free flows and porous/rough
materials using effective boundary conditions, that is, without resolving every microscopic feature
of the surface. These problems illustrate the potential of surface engineering for control of
transport phenomena and our ability to efficiently model flows over complex surfaces.
Shervin Bagheri is a Professor at the Royal Institute of Technology, KTH in Stockholm. He is a
Wallenberg Academy Fellow and one of the twenty recipients of the Future Research Leaders grant
awarded by the Swedish Foundation for Strategic Research. His research group (www.bagherigroup.com)
focuses on understanding how flowing fluids and surfaces behave and interact across length scales,
including modelling moving triple-phase moving contact lines, lubrication forces, transport in
porous media and wall-bounded turbulent flows. His group uses mainly numerical simulations in
combination with multiscale, data-driven and/or modal techniques for analyzing and controlling
fluid-surface interaction.
2021 AFMSS: Aerodynamically driven rupture of a liquid film by turbulent shear flow
Melissa Kozul
University of Melbourne
4.00pm Wednesday 31 March 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
The rupture of a liquid film due to co-flowing turbulent shear flows in the gas phase is studied
using a volume-of-fluid method. This was done by ‘sandwiching’ the liquid film between two fully
developed gas-phase boundary layers from a turbulent channel simulation. The film deforms and
eventually ruptures within the shear zone created by the co-flows. Previous theoretical work has
indicated that aerodynamic forces drive the film’s evolution. We employ a classical aerodynamics
approach to quantify the role of the inviscid lift and drag forces over the deforming film, which
while suggested by previous authors, has not been systematically studied before. A cumulative lift
force is introduced to capture the effect of the alternating pressure minima and maxima forming
over the film, which amplify and eventually rupture the film. Our novel, efficient setup allows
systematic variation of physical parameters to gauge their role in the aerodynamically driven
deformation and rupture of a liquid film under fully developed sheared turbulence.
Melissa completed her PhD at the University of Melbourne in 2018 under the supervision of A/Prof.
Daniel Chung and Prof. Jason Monty, having completed undergraduate degrees at the same institution.
In early 2018 she moved to Norway and was a Postdoctoral Fellow within the Thermo Fluids Research
Group at NTNU in Trondheim for three years. She has recently been engaged as a Research Fellow at
the University of Melbourne upon returning to Australia. Melissa’s research expertise is in the
high-fidelity simulations of fundamental turbulent flows that feature critically in energy and
transport technologies, for which she often employs strategically-designed numerical ‘thought
experiments’ to decouple effects that are conflated, or add controlled physics. To date her
research interests have included wall-bounded flows, homogeneous isotropic turbulence, turbulent
multiphase flows as well as particle tracking and sizing algorithms for use with laboratory
turbulent flows.
2021 AFMSS: Swept-wing boundary layer transition
Yury S. Kachanov
Khristianovich Institute of Theoretical and Applied Mechanics
7.00pm* Wednesday 24 March 2021 (*Please note change in start time)
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
A brief review of recent very impressive advances achieved during past ten years in experimental
(basically) investigations of the laminar-turbulent transition scenarios, prediction, and control
in swept-wing boundary layers is presented. The cases of the transition scenarios dominated by the
crossflow (CF) instability and 3D Tollmien-Schlichting (TS) instability are considered. All stages
of the transition processes are discussed, including various mechanisms of flow receptivity to external
perturbations, flow instabilities, and secondary instabilities, as well as final flow turbulization.
The problem of excitation of CF- and TS-instability modes in swept-wing boundary layers by various
external perturbations, such as steady and unsteady surface nonuniformities, freestream vortices, and
acoustic waves, is discussed. Mechanisms of both localized and distributed receptivity are analyzed and
question of relative efficiency of these mechanisms is discussed. A statement about existence of a
universal mechanism of beginning of the flow turbulization in 3D boundary layers on swept wings with
CF-instability dominated transition is made and substantiated. This mechanism is common for all
evolutionary transition scenarios at conditions of presence (or absence) of various surface
imperfections and various freestream vortical perturbations both steady and unsteady ones. In contrast
to 2D boundary layers, such universal mechanism is associated with spatially localized high-frequency
secondary instability of the base flow perturbed by development of primary steady and unsteady
disturbances associated with the CF-instability. A problem of existence of a simple universal criterion
of beginning of the boundary layer turbulization is discussed.
It is shown that such criterion has been found and can be used successfully at present by advanced
transition prediction approaches. This is the criterion of instantaneous threshold amplitude of combined
CF-instability modes (sum of instantaneous maximum amplitudes of steady and unsteady perturbations).
A problem of theoretical calculation of the combined amplitudes is also discussed. Problem of reduction
of disturbance amplitudes and transition delay by means of excitation of steady and traveling CF-modes
by application of surface roughness elements and acoustic waves is discussed. There is a great recent
advancement in experimental research of the problem of laminar-turbulent transition in swept-wing
boundary layers. However, a lot of questions remain and a lot of problems wait for their solution.
Yury S. Kachanov is a professor in Fluid and Plasma Mechanics, Main Research Scientist and Head of
Research Group in Khristianovich Institute of Theoretical and Applied Mechanics of Siberian Branch
of the Russian Academy of Sciences Novosibirsk, Russian Federation. He has received the Alexander
von Humboldt Research Award in 2002, the highest prize of the German Aerospace Society:
“Ludwig-Prandtl-Ring” in 2008, and the Prof. G.I. Petrov’s Prize of the Russian National Committee
on Theoretical and Applied Mechanics in 2010. His fields of interest are receptivity and stability
characteristics of boundary layers to various external perturbations, traveling and steady instability
modes, nonlinear mechanisms of breakdown of laminar boundary layers, nonlinear interactions of
instability modes in boundary layers, mechanisms of formation, development, and breakdown of coherent
structures in transitional and turbulent flows, mechanisms of turbulence production at late stages of
transition.
2021 AFMSS: Numerical analysis of heat transfer characteristics of wall impinging spray flames under CI engine-like conditions
Abhishek L. Pillai
Kyoto University
4.00pm Wednesday 17 March 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Design of Compression Ignition (CI) engines with improved thermal efficiencies requires further
investigation of the heat transfer mechanism from spray flame to the combustion chamber wall. Heat
transfer during the interaction between impinging spray flame and wall under CI engine-like conditions,
is investigated in this study using 3-D numerical simulations. The main objective is to examine the
influence of fuel spray injection velocity on the heat transfer between impinging spray flame and wall.
Details of the numerical methods and models employed in these simulations will be discussed. Results
obtained from the simulations indicate that the total heat flux (sum of convective and radiative heat
fluxes) at the wall surface increases with the fuel injection velocity. It is observed that the total
wall heat flux is largest in the stagnation zone where the spray flame impinges directly upon the wall
surface, while the radiative heat flux at the wall surface becomes greater as the distance form this
stagnation zone increases. Additionally, it is found that the influence of fuel injection velocity on
the radiative heat flow rate at the wall surface is rather insignificant. This radiative heat flow rate
when expressed as a percentage of the total wall heat flow rate, ranges from ≈ 18% to 30% (depending on
the 3 cases investigated), indicating that its contribution cannot be neglected for the CI engine-like
conditions under which the present simulations are performed. Furthermore, correlations between the
Nusselt number Nu (corresponding to the wall heat loss) and Reynolds number Re (of the flow-field) of
the form
, are analysed and compared with those of existing experimental studies to assess
their applicability for accurately estimating the heat transfer coefficient.
Abhishek is an Assistant Professor in the Department of Mechanical Engineering and Science at Kyoto
University. He completed his PhD (Engineering) at Kyoto University under the supervision of Prof
Ryoichi Kurose and is a recipient of the prestigious Japanese Government (Monbukagakusho) PhD
Scholarship. He holds a Master’s degree in Aerospace Engineering from the Indian Institute of Technology
(IIT) Bombay. He is also a member of the Japan Society of Mechanical Engineers (JSME). His main research
interests lie in numerical investigations of problems pertaining to turbulent combustion, occurring
under conditions relevant to practical energy conversion devices (viz., gas-turbines, IC engines).
Therefore, he performs large-scale parallel simulations on HPC infrastructures, such as Direct Numerical
Simulation (DNS) and Large-Eddy Simulation (LES), for studying turbulent gas-phase and spray combustion
problems. His recent research focuses on thermo-acoustic instabilities, combustion noise using hybrid
CFD/CAA (Computational Fluid Dynamics/Computational Aero-Acoustics) simulations, and wall-bounded
turbulent reacting flows.
2021 AFMSS: High-order finite-difference schemes on a cartesian mesh: application to active flow control of turbulent flows
Sylvain Laizet
Imperial College London
6.00pm* Wednesday 10 March 2021 (*Please note change in start time)
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
With recent impressive developments in computer technology, High Performance Computing (HPC) is
currently transitioning to the exascale era with far-reaching consequences for scientific research.
HPC is expected to open the doors to solving highly complex turbulence problems that were until
very recently beyond our imagination. Computational Fluid Dynamics (CFD) is now a critical complement
to experiments and theories in order to understand turbulent flows and discover strategies to
manipulate them. One of the biggest challenges for the CFD community is to be able to efficiently
exploit the current and next generation of HPC systems. In this talk, I will introduce the open-source
framework Xcompact3d, dedicated to the study of turbulent flows on HPC systems based on CPUs. Based
on high-order finite-difference schemes on a Cartesian mesh, it combines accuracy, efficiency,
versatility and scalability. Active flow control solutions for wall-bounded flows, free-shear flows
and wind turbines will be presented to highlight the potential of the Xcompact3d framework.
Sylvain Laizet is a reader in the Department of Aeronautics at Imperial College London (ICL). He
holds a PhD and an Habilitation à Diriger des Recherches from the University of Poitiers in France
in the field of Computational Fluid Dynamics (CFD) applied to turbulence. Understanding turbulent
flows and how to manipulate them in various engineering applications is the motivation behind his
research. With his collaborators at Imperial College, in France and in Brazil, he has developed
over the years high-order finite-difference highly-scalable flow solvers dedicated to the study
turbulent flows. Within the turbulence simulation group at ICL, he is currently investigating
wake-to-wake interactions in wind farms, Bayesian optimisation techniques for drag reduction and
energy saving, active control solutions for free-shear flows, immersed boundary methods for moving
objects, neural networks applied to CFD and particle-laden gravity currents.
2021 AFMSS: Eddy structures and very-large-scale motions in turbulent round jets
Milad Samie
Queen's University
4.00pm Wednesday 3 March 2021
Online Event (2021 Australasian Fluid Mechanics Seminar Series)
Coherent structures in the fully turbulent region of round jets are evaluated for up to
Re_d=50,000 with the aid of two-point measurements and an existing direct numerical simulation
(DNS) dataset. The experimental data comprise simultaneous velocity time-series acquired with
both radial and azimuthal separations between the sensors. A spectral correlation analysis is
applied to these data that reveal that the coherent structures in the jet flow consist of two
rincipal configurations, which correspond to two main spectral domains. One spectral domain,
which is signified by small to medium wavelengths, is associated with hierarchical eddy
structures (ESs) for which a physical aspect ratio of 1.2:1:1 in the axial, radial, and
azimuthal directions is observed. The other spectral domain indicated by large wavelengths
is associated with very-large-scale-motions (VLSMs). The wavelength marking the boundary between
these spectral domains is used to decompose the velocity fluctuations into ES and VLSM components,
and the corresponding ES and VLSM components of two-point correlations are obtained from the
experimental data. The VLSM component of two-point correlations denotes helical structures as
the dominant VLSMs in the jet turbulent region. Instantaneous axial velocity fluctuation fields
from DNS support the prevalence of helical VLSMs in the jet. Moreover, the ES signatures are
evident in the unwrapped axial-azimuthal planes of the DNS, indicating that the VLSMs are formed
by the concatenation of ESs.
Milad is an adjunct professor and a postdoctoral research fellow at Queen’s University. Milad
received his PhD degree from the University of Melbourne under the supervision of Professors
Ivan Marusic and Nicholas Hutchins in 2018 before moving to Queen’s University. Milad uses
experimental and theoretical methods to study various fundamental flow physics including wall
bounded turbulent flows, free shear flows, entrainment, coherent structures, and active flow
control.
2020 AFMSS: Host-to-Host Airborne Contagion As a Multiphase Flow Problem For Science-Based Social Distance Guidelines
Sivaramakrishnan Balachandar
University of Florida
4.00pm Wednesday 2 December 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
The COVID-19 pandemic has brought sudden and broad social awareness about the fundamental role
of airborne droplets and aerosols as virus carriers. Droplets are formed and emitted at high
speed during a sneeze, and at lower speed while coughing, talking or breathing. But no two
coughs or sneezes are alike - many aspects of these expiratory events vary from one individual
to another. For example, a violent sneeze of a large person could generate a large puff
containing a sizable number of potentially virus-laden droplets that extend much farther into
the surrounding than that of a child. It is to be expected that the coughs and sneezes of even
the same individual could vary from one to the next. It is perhaps less evident that two nearly
identical coughs or sneezes may show substantial differences as a result of their turbulent
nature. Infinitesimal differences in the initial exhalation process or in the ambient conditions
can be dramatically amplified and send a cough or sneeze careening in different paths - this
chaotic behavior is the so-called butterfly effect. Such chaotic evolution must be properly
accounted in any deterministic social distancing guidelines, since such guidelines must not only
safeguard under average conditions, but also take into account occasional extreme departures
from the average. Despite the chaotic behavior, there are important underlying universal
properties that are common across all expiratory events and the dispersive nature of the ejected
droplet clouds. This work will demonstrate the ability of a simple mathematical formulation
(Balachandar et al., Int J. Multiphase Flow, 2020) to accurately predict the key quantities of
interest to viral contagion. Furthermore, the simulations, supported by theoretical analysis,
illustrate the importance of environmental variables such as dry versus humid condition can have
on the number of airborne airborne potentially virus-laden droplet nuclei.
Sivaramakrishnan Balachandar is a Distinguished Professor in Mechanical & Aerospace Engineering
at the University of Florida.
2020 AFMSS: Stabilisation of exact coherent structures using time-delayed feedback in two-dimensional turbulence
Dan Lucas
Keele University
6.00pm* Wednesday 25 November 2020 (*Please note change in start time)
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Time-delayed feedback control (Pyragas 1992 Phys. Letts. 170 (6) 421-428), is a method known
to stabilise periodic orbits in chaotic dynamical systems. A system dx/dt = f(x) is supplemented
with G(x(t)-x(t-T) where G is a `gain matrix' and T a time delay. The form of the delay term
is such that it will vanish for any orbit of period T, making it an orbit of the uncontrolled
system. This non-invasive feature makes the method attractive for stabilising exact coherent
structures in fluid turbulence. Here we validate the method using the basic flow in Kolmogorov
flow; a two-dimensional incompressible viscous flow with a sinusoidal body force. Linear
predictions for the laminar basic flow are well captured by direct numerical simulation.
This result demonstrates a work-around of the so-called “odd-number” limitation in flows which
have a continuous symmetry. By applying an adaptive method to adjust the streamwise translation
of the delay, a known nonlinear travelling wave solution is able to be stabilised up to
relatively high Reynolds number. Finally an adaptive method to converge the period T is also
presented to enable periodic orbits to be stabilised in a proof of concept study at low Reynolds
numbers. These results demonstrate that unstable ECSs may be found by timestepping a modified
set of equations, thus circumventing the usual convergence algorithms.
Dan holds an undergraduate MMath degree in Applied Mathematics from the University of St Andrews
and an MSc in Atmosphere/Ocean modelling from Reading University. Following this he returned to St
Andrews to study for his PhD under the supervision of Prof David Dritschel. Dan then held
postdoctoral positions in Bristol (Rich Kerswell), University College Dublin (Miguel Bustamante)
and Cambridge (Colm Caulfield) before starting as a lecturer in Applied Mathematics at Keele
University in September 2017.
2020 AFMSS: Nonlinearity - the “frenemy” of linearised Navier-Stokes analysis
Sean Symon
University of Southampton
6.00pm* Wednesday 18 November 2020 (*Please note change in start time)
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
The linearised Navier-Stokes equations are a popular tool for identifying structures in
turbulent flows. There are, nevertheless, subtle differences between the structures computed
directly from the flow using data-based methods (e.g. dynamic mode decomposition) and
equation-based methods (e.g. resolvent analysis). In this talk, we scrutinise the nonlinear
forcing term, which is often treated as white noise in space and time, for three flows of
increasing complexity. The first is flow past a circular cylinder, where we deal explicitly
with the nonlinear forcing. We show that linear analysis provides clues regarding the
nonlinear interactions that are needed to sustain the flow. The second is an exact coherent
state in plane Poiseuille flow, where we analyse the energy balance and compare it to
predictions from resolvent analysis. We also investigate the quantitative agreement between
nonlinear transfer modelled by an eddy viscosity profile to the true nonlinear transfer.
Finally, we consider turbulent channel flow at Reτ = 2003, where we make no attempt to
compute or model the nonlinear forcing. Instead, we investigate how an imperfect eddy viscosity
can be corrected by limited measurements to build a useful estimator of the flow.
Sean studied Aerospace Engineering at the University of Maryland where he completed a Bachelor
of Science and a Bachelor of Arts in French Language/Literature in 2012. The following year,
he completed a Master of Science in Aeronautics at the California Institute of Technology.
Before beginning his PhD, Sean studied at Ecole Polytechnique in Paris where he was awarded
a masters in fluid mechanics in 2014. He returned to Caltech for his PhD under the supervision
of Beverley McKeon. Sean defended his thesis in 2018 and became a post-doctoral research
fellow in Australia for 2 years at the University of Melbourne, working with Simon Illingworth
and Ivan Marusic. He began as a lecturer in the Aerodynamics and Flight Mechanics Group in
2020 at the University of Southampton.
2020 AFMSS: Turbulence structure and modeling: some adventures in the frequency domain
Tim Colonius
Caltech
6.00pm* Wednesday 11 November 2020 (*Please note change in start time)
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Amongst many available data-driven modal decompositions of utility in fluid mechanics, the
frequency-domain (spectral) version of the proper orthogonal decomposition (SPOD) plays a
special role in the analysis of stationary turbulence. SPOD modes are optimal in expressing
structures that evolve coherently in both space and time, and they can be regarded as
optimally-averaged DMD modes. Importantly, the SPOD spectrum is also related to the resolvent
spectrum of the linearized dynamics and examination of the relationships between the SPOD and
resolvent modes yields information about how coherent structures are forced by nonlinear
interactions amongst coherent and incoherent turbulence. We discuss the application of these
tools to analyze and model turbulence in high-speed jets and boundary layers. We highlight
recent developments including (a) utilizing eddy-viscosity models in resolvent analysis to
enable RANS-based prediction of coherent structures, and (b) nonlinear extensions of resolvent
analysis to discover worst-case disturbances for laminar-turbulent transition, and (c) the
development fast spatial marching methods for large-scale resolvent problems.
Tim Colonius is the Frank and Ora Lee Marble Professor of Mechanical Engineering at the
California Institute of Technology. He received his B.S. from the University of Michigan in
1987 and M.S and Ph.D. in Mechanical Engineering from Stanford University in 1988 and 1994,
respectively. He and his research team use numerical simulations to study a range of problems
in fluid dynamics, including aeroacoustics, flow control, instabilities, shock waves, and bubble
dynamics. Prof. Colonius also investigates medical applications of ultrasound, and is a
member of the Medical Engineering faculty at Caltech. He is a Fellow of the American Physical
Society and the Acoustical Society of America, and he is Editor-in-Chief of the journal
Theoretical and Computational Fluid Dynamics. He was the recipient of the 2018 AIAA Aeroacoustics
Award.
2020 AFMSS: Navigating turbulent waters
Ashleigh Hutchinson
University of the Witwatersrand
4.00pm Wednesday 4 November 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Approaches to modelling turbulence vary in complexity. From simple eddy viscosity closure
models to complicated numerical simulations, all methods have their uses depending on the
context in which they are to be applied. Turbulence is commonly observed in nature and in
industry. Physicists and engineers alike aim to design reliable models that are of theoretical
and industrial importance. However, this endeavour proves challenging and progress can only be
made when theoretical, experimental, and computational approaches are integrated. Despite
having these techniques at our disposal, turbulence is considered ‘one of the oldest unsolved
problems’ in Physics. In this talk, provide an overview of the different approaches to
modelling turbulence. We will focus on one application, turbulent wakes, which play a valuable
role in the design, maintenance, and control of turbines on wind farms. Various eddy viscosity
closure models will be investigated and compared.
Dr Ashleigh Jane Hutchinson is a Senior Lecturer at the University of the Witwatersrand,
Johannesburg, in the School of Computer Science and Applied Mathematics, in the Faculty of
Science. She is also the Assistant Director of the national DSI-NRF Centre of Excellence in
Mathematical and Statistical Sciences (CoE-MaSS). The focus of Dr Hutchinson’s research is on
developing mathematical models to solve real-world problems, with particular attention paid to
modelling in fluid mechanics. Her research is a combination of theoretical work and practical
applications.
2020 AFMSS: Patterns in 2D Turbulence: Cause, Effect and Monte-Carlo Science
Javier Jiménez
Universidad Politécnica de Madrid
7.00pm* Wednesday 28 October 2020 (*Please note change in start time)
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
The relentless growth of the speed of computers has meant that turbulence simulations that
used to take long times can now be performed in minutes. Among other things, this allows us
to explore ideas ‘at random’, in the hope that some of them might be interesting, but this
‘Monte-Carlo science’ is only the first step in a process in which the choice and evaluation
of ideas still has to be performed by human researchers in more conventional way. The most
important role of the computer is to help them overcome their prejudices. We will explore an
example of such a (humanmachine) collaboration dealing with the dynamics of the reverse energy
cascade in two-dimensional turbulence. It begins with the essentially random search for local
flow perturbations that result in global effects, continues with the identification of the
sensitive flow patterns where these perturbations are best applied, and eventually guides us
to the formation process of large-scale vortex patterns. Although the (human) author accepts
responsibility for most of the analysis and conclusions, he has to acknowledge that the
original idea came from the computer.
Javier Jiménez is an emeritus research professor at the School of Aeronautics of the U.
Politécnica de Madrid, Spain. He received his Engineering degree from the same school, and a
PhD in Applied Mathematics from Caltech. After beating about several bushes, his main interest
for the past few years has been to deceive himself into believing that turbulence is really
simple. His coauthor in this particular talk, Mr. PLOFF, is a computer.
2020 AFMSS: High-fidelity simulations for cleanear gas turbines
Mohsen Talei
University of Melbourne
4.00pm Wednesday 21 October 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Gas turbines are the predominant prime movers in the aviation industry and account for about
20% of the installed capacity for electricity generation globally. They have fast ramp up
and down capabilities, which make them complementary to intermittent renewable generation.
Furthermore, with the increasing interest in producing renewable hydrogen, gas turbines can
play an important role in the implementation of a successful hydrogen economy.
Lean premixed combustion is the desired combustion regime in industrial gas turbines. It
results in a low level of NOX emissions due to operating at lower temperatures and facilitates
better combustion efficiency. However, the main issue with operating gas turbines in this
regime is thermoacoustic instability, commonly initiated by combustion-generated sound. Another
problem with these gas turbines is the increase in carbon monoxide (CO) emissions at part-load
and low temperatures. These issues are significant drawbacks for developing cleaner gas turbines
that feature stable combustion.
High-fidelity simulations such as direct numerical simulation (DNS) can play a critical role here.
They can provide insight into the root cause of these issues and the rich data provided by the
simulations can help us develop more accurate predictive models. This presentation will provide
examples from DNS studies undertaken at the University of Melbourne in this context.
Dr. Mohsen Talei is a Discovery Early Career Researcher (DECRA Fellow) of the Australian
Research Council (ARC) and a Senior Lecturer in the Department of Mechanical Engineering.
Mohsen joined the University of Melbourne as a staff member in 2014, having previously completed
post-doctoral research at the University of New South Wales (UNSW) and a PhD at the University
of Melbourne. Mohsen has 17 years of industry and academic research experience in the broad area
of energy, which includes numerical and theoretical investigations of turbulent reactive flows
with a focus on low-emission energy technologies. Mohsen’s research involves a significant use
of high-performance computing to develop reliable models that can be used for simulating cleaner
gas turbines and reciprocating engines.
2020 AFMSS: Symmetry induced turbulent scaling laws for arbitrary moments and their validation with DNS and experimental data
Martin Oberlack
Technische Universität Darmstadt
4.00pm Wednesday 14 October 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Using the symmetry-based turbulence theory, we derive turbulent scaling laws in wall-bounded
shear flows for arbitrarily high moments of the flow velocity
. The key ingredients are the
symmetries of classical mechanics, especially the scaling of time and space, and two statistical
symmetries, which are not directly visible in Euler and Navier-Stokes equations. These symmetries
are admitted by all complete theories of turbulence, i.e. the infinite hierarchy of moment and
PDF equations and also by the famous Hopf functional approach. The symmetries provide a measure
of intermittency and non-Gaussian behavior – properties that have been investigated for decades
for turbulence and are now subject to a rigorous description. Based on this, in the near-wall
log-region the symmetry theory predicts an algebraic law with the exponent
)
for moments
. Hence, the exponent
of the 2nd moment determines the exponent of all higher moments.
Moments here always refer to the instantaneous velocities
and not to the fluctuations
. For
the core regions of both plane and round Poiseuille flows we find a deficit law for arbitrary
moments
of algebraic type with a scaling exponent
 + 2 s_1 - s_2)
. Hence, the moments
of order one and two with its scaling exponents
and
determine all higher exponents. All
new theoretical results will be nicely validated by a new channel flow DNS at
and data from the CICLoPE pipe flow experiment at
.
Martin Oberlack is Professor of Mechanical Engineering at Darmstadt University and holder of
the chair for fluid dynamics. He received both his Diploma (1988) and his Ph.D. (1994) from
RWTH Aachen. Prof. Oberlack pioneered the use of Lie symmetry methods for the study of turbulence
and modelling concepts and has written widely on this with a special focus on turbulent shear
flows. His current interests include: Lie symmetries of the Lundgren-PDF and Hopf equation of
turbulence, construction of conservation laws, hydrodynamic stability theory, Fokas unifying
method for multi-phase problems, aerodynamic noise, combustion, high-performance and parallel
computing, GPU acceleration, Discontinuous Galerkin numerical methods with special focus on
singular problems such as multi-phase flows and large scale direct turbulence simulations. He
was and is actively involved in various editorial boards including Fluid Dynamic Research,
Theoretical and Computational Fluid Dynamics and Continuum Mechanics and Thermodynamics. He
is a Fellow of the American Physical Society for his pioneering use of symmetry methods for
the study of turbulence and related fields and the derivation of new conservation laws in fluid
dynamics.
2020 AFMSS: Numerical investigation of shock-induced phenomena in turbulent flows
Ivan Bermejo-Moreno
University of Southern California
4.00pm Wednesday 07 October 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
This talk will address fundamental interactions between shock waves and turbulent flows
relevant to high-speed flight and propulsion:
Shock-induced scalar mixing under canonical shock-turbulence interactions (STI) will be
considered first, by means of Direct Numerical Simulation. The effects of relevant physical
parameters (shock and turbulence Mach numbers, and Reynolds number) will be highlighted on
statistical changes along the shock-normal direction of scalar variance and dissipation-rate
budgets, as well as alignments of the scalar gradient with vorticity and strain-rate
eigendirections. Shock-induced scalar mixing will also be addressed by tracking the downstream
evolution of the geometry and physics of scalar structures initialized with a well-defined shape
as they are transported and diffused by the background turbulence in STI, and compared with
decaying homogeneous isotropic turbulence.
Flow-structure interactions of shock waves reflecting off turbulent boundary layers that develop
along flexible walls will be addressed next, comparing results from ongoing numerical
simulations with prior wind tunnel experiments. The calculations couple wall-modeled large-eddy
simulation for the fluid flow, using an Arbitrary Lagrangian-Eulerian formulation, with an elastic
solid structural solver that accounts for geometric nonlinearities, and a mesh deformation module
based on a spring-system analogy. Strong shock/boundary-layer interactions resulting in mean flow
separation and low-frequency unsteadiness that can interact with the natural frequencies of the
structure will be emphasized.
Ivan Bermejo-Moreno received his Ph.D. in aeronautics (2008) from the California Institute of
Technology. Afterwards, he held a postdoctoral research fellowship at the Center for Turbulence
Research, Stanford University/NASA Ames Research Center (2009-2014). He joined the Aerospace and
Mechanical Engineering Department at the University of Southern California in 2015. His research
combines numerical methods, physical modeling and high-performance computing for the simulation
and analysis of turbulent fluid flows involving multi-physics phenomena. He is a recipient of the
Fulbright Fellowship, the Rolf D. Buhler Memorial Award, the William F. Ballhaus Prize and the
Hans G. Hornung Prize.
2020 AFMSS: Self-excited three-dimensional laminar separation bubbles: Waypoints in a 20-year roadmap
Vassilis Theofilis
University of Liverpool
5.00pm* Wednesday 30 September 2020 (*Please note change in start time)
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Solutions of multi-dimensional initial-value and eigenvalue problems that govern linear
instability of flow in the vicinity of laminar separation bubbles forming in boundary layers
from incompressible to hypersonic flow have permitted placing knowledge gained from simplified
local analyses on a firmer theoretical footing and revealed physical mechanisms of separated
flow instability inaccessible to classic linear theory. The first part of the talk will discuss
the footprints of the dominant stationary and traveling primary and secondary global eigenmodes
as well as linear optimal disturbances of spanwise homogeneous incompressible laminar separated
flows over wings and low pressure turbine blades. Results will be contrasted against recently
obtained linear global modes on finite aspect ratio swept wings. In the second part of the talk,
the laminar separation bubble formed at a compression corner in supersonic flow will be shown to
sustain linear instabilities in which the recompression shock forms an integral part of the
amplitude functions of the dominant global modes, a result which renders questionable instability
analyses in which shocks (or their effects) are neglected. An analogous conclusion is reached in
shock-induced laminar separation bubble in hypersonic flow over double cones and double wedges,
where both two- and three-dimensional global instability analysis has shown the intimate
connection (through the global mode amplitude functions) of instability in the laminar separation
zone, the triple point, the slip line and the shock system downstream of the laminar separation
bubble.
Prof. Theofilis obtained his MSc in Applied Mathematics and PhD in Aerospace Engineering at the
University of Manchester. After a post-doc at the Department of Applied Mathematics of University
of Twente, he has been Alexander von Humboldt research fellow at DLR Goettingen, Germany and
Ramon y Cajal Research Professor at the School of Aeronautics in Madrid. He held visiting
appointments at Caltech, Arizona, Maryland and the Universidad Federal Fluminense (Rio de
Janeiro). In 2016 he was appointed at the Chair of Aerospace Engineering at the University of
Liverpool and since 2019 he is also Full Professor at the Escola Politecnica of Universidade São
Paulo. His research interests lie in development and application of accurate numerical methods
for the solution of large-scale eigenvalue and singular value problems, as applied to fluid flow
nstability from the incompressible to the hypersonic regime.
2020 AFMSS: Spectral properties of turbulence kinetic energy in turbulent boundary layers
Woutijn Baars
TU Delft
4.00pm Wednesday 23 September 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Even though wall-bounded turbulence is highly broadband in nature, it does comprise a strong
coherence in for instance the velocity fields. This seminar will primarily focus on a spectral
characterization of organized motions in wall-bounded turbulence. An organization is evidenced
by the longstanding classification of different flow structures, such as hairpin packets and
very large-scale motions. Since the turbulence statistics of different categories of structures
comprise dissimilar scaling behaviors, their coexistence complicates the development of scaling
laws or models for velocity spectra and even the integrated turbulence kinetic energy. Via
multi-point data analyses, we present data-driven spectral filters for stochastically
decomposing velocity spectra into sub-components, which are interpreted as representations of
different types of ‘building blocks’ of the wall-bounded turbulent flow. In the process we
reveal a Reynolds-number invariant wall-scaling for a portion of the outer-region turbulence
that is coherent with the near-wall region; this supports the existence of wall-attached
self-similar turbulent structures. Throughout this seminar we will also indicate how the results
assist in developing frameworks for predicting statistics at high-Reynolds-number conditions,
how they assist in designing active control methods and how they assist in creating models for
coherent turbulence in atmospheric surface layers.
Woutijn Baars is an Assistant Professor in the Faculty of Aerospace Engineering at Delft
University of Technology, within the sections of aerodynamics and aeroacoustics. His research
interests span various topics related to turbulence, including wall-bounded turbulence and
passive/active methods for flow-control, and the aeroacoustics of turbulent jet flows rotor
systems (propulsion of drones and urban air mobility vehicles). Woutijn received his MSc degree
(2009) from Delft University of Technology and his PhD degree (2013) from the University of
Texas at Austin, where he primarily focused on experimental jet aeroacoustics. From 2013 to
2018 he was a Research Fellow at the University of Melbourne, focusing on the flow physics of
high-Reynolds-number wall-bounded turbulence.
2020 AFMSS: Mixing enhancement in binary fluids by adjoint-based optimization
Peter Schmid
Imperial College London
4.00pm Wednesday 16 September 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
The mixing of binary fluids by stirring is a ubiquitous process in a wide range of
industrial applications. The food processing, pharmaceutical and consumer product industries
are dominated by mixing processes, and enhancing mixing efficiency for these applications,
even by a very modest amount, would translate into considerable savings and benefits. We
develop and use an adjoint-based nonlinear optimization scheme to minimize the mix-norm of
a passive scalar. The mixing is accomplished by two cylindrical stirrers, moving on
concentric circular paths inside a circular container. In a first attempt, the velocities of
these stirrers is optimized to reach improved mixedness over a finite time horizon. The
enhanced stirring protocol is shown to consist of a complicated interplay of vortical
structures which have been created and exploited by the stirrers’ action. In a second attempt,
and within the same computational framework, we seek to optimize the cross-sectional shape of
the stirrers. In both scenarios, substantial mixing enhancement could be achieved. Further
extensions of the mathematical formalism and the physical setup will be discussed, and
remaining challenges of this research effort will be addressed.
Prof. Peter Schmid received his Engineer's Degree from the Technical University Munich and
his PhD in mathematics from the Massachusetts Institute of Technology. He then joined the
Department of Applied Mathematics of the University of Washington, Seattle before taking up a
research director position with the French Scientific Research Agency (CNRS) at the
Laboratoire d'Hydrodynamique (LadHyX) of the Ecole Polytechnique near Paris. He is currently
Chair of Applied Mathematics and Mathematical Physics in the Department of Mathematics of
Imperial College London. His research focuses on stability theory, flow control, model
reduction and computational fluid dynamics. He is also interested in data decomposition
techniques and algorithms for the extraction of pertinent flow processes from numerical
and experimental data.
2020 AFMSS: Canopy Flows - An Outsider's Look
Ricardo Garcia-Mayoral
University of Cambridge
4.00pm Wednesday 09 September 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
The turbulent flow over and within canopies is a subject of interest to both engineering
applications and to hydrology and atmospheric fluid dynamics. By 'canopy' we refer to a
collection of elements that obstruct the flow, which are "tall" -in a rather vague sense-
to differentiate them from conventional roughness. This talk will discuss our recent work
on canopy flows, approaching the problem from a background in turbulence over textured
surfaces and flow control. We focus mainly on the character of the flow for homogeneous
canopies of different densities, and use evidence from direct simulations. We observe that
the flow dynamics arise from the interplay between the overlying turbulence, the
element-induced flow, and the mixing-layer instability that can be induced at the canopy-tip
plane. For sparse canopies, only the first two mechanisms are present. The turbulence
in-between elements is essentially unobstructed, and is thus reminiscent of that over a
smooth wall, but scaling with the fluid shear at each height. As the canopy density
increases, mixing-layer rollers develop and the flow within the canopy becomes more
quiescent, showing only a damped footprint of the overlying rollers. The element height has
a secondary influence on the flow, as a lack of sufficient canopy depth inhibits the
mixing-layer instability. From the evidence in our simulations, we argue that the ratio of
the element spacing to the turbulent scales is the essential parameter determining whether
the canopy behaves as dense or sparse.
Dr. Ricardo Garcia-Mayoral received his PhD from Universidad Politécnica de Madrid in 2011
under Prof. Javier Jiménez, and subsequently was a Postdoctoral Scholar at the Center for
Turbulence Research in Stanford University in 2012-2013. Since 2013 he has been a Lecturer
in Fluid Mechanics at the Department of Engineering in the University of Cambridge, UK. His
group's research focuses on understanding the dynamics of turbulent flows over
non-conventional surfaces, and on how these surfaces can modify and control the flow. The
group has worked on roughness, riblets, superhydrophobic surfaces, canopies, and permeable
substrates.
2020 AFMSS: DMD-based methods to identify flow patterns
Soledad Le Clainche
Universidad Politécnica de Madrid
4.00pm Wednesday 02 September 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Complex flows model a wide range of industrial and biological applications. Although
these flows have been studied for decades, due to their high complexity, to elucidate
their spatio-temporal structure is still considered as an open topic in a large quantity
of relevant cases. Hence, the deep study and understanding of complex flow behavior,
such as transitional or turbulent flows, is a research topic of high interest. In this
talk we will introduce a method suitable to detect spatio-temporal patterns in complex
non-linear dynamics. This is an extension of the well-known technique dynamic mode
decomposition (DMD), called as higher order dynamic mode decomposition (HODMD). The method
combines singular value decomposition (SVD) with DMD and Takens' delay embedding theorem
to approximate the main dynamics describing a signal. HODMD has been successfully applied
to study several problems covering from non-linear dynamical systems (i.e. complex
Ginzburg-Landau equation, Lorenz system), to complex fluid dynamic problems (i.e. analysis
of noisy experiments and transitional flows in synthetic jets, turbulent channel flows,
etcetera) and has also been applied as a reduced order model for data forecasting in
compressible flows and wind turbines. In the second part of the talk, a method known as
spatio temporal Koopman decomposition (STKD) will be introduced, presenting a good
alternative to perform spatio-temporal DMD analyses in a very efficient way. This method
identifies coherent structures as a group of traveling waves. The method will be tested
in some examples including the detection of spatio-temporal flow structures describing
the wake of a wind turbine or global instabilities in elastoviscoplastic fluids and
turbulent channel flows with anisotropic porous wall. The main flow patterns will be
identified, and this information will be used to create a reduced order model for data
forecasting.
Dr. Soledad Le Clainche holds a Lectureship in Applied Mathematics at the School of
Aerospace Engineering of UPM. She received a Master in Mechanical Engineering by UPCT,
in Aerospace Engineering by UPM, and in Fluid Mechanics by the Von Karman Institute.
In 2013 she completed her PhD in Aerospace Engineering at UPM. Her research focusses
on computational fluid dynamics and in the development of novel tools for data analysis
enabling the detection of spatio-temporal patterns. Recently, she has developed reduced
order models taking advantage of the insights provided by data analysis tools. In
addition, she has contributed to the fields of flow control, global stability analysis,
synthetic jets, analysis of flow structures in complex flows (transitional and turbulent)
using data-driven methods, and prediction of temporal patterns using machine learning and
soft computing methods.
2020 AFMSS: Prediction of Structural Wind Loading and Aerodynamic Scaling Effects due to Atmospheric Boundary Layer Turbulence
Matthew Emes
University of Adelaide
4.00pm Wednesday 26 August 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Wind load predictions for small-scale structures, such as heliostats, are not provided
in design codes for buildings because of their thin-walled structural components and
the changes in wind velocity and turbulence in the lowest 10 m of the atmospheric
boundary layer (ABL). This seminar will provide an insight into the generation and
analysis of turbulence characteristics within simulated ABLs in the large-scale
University of Adelaide wind tunnel. Through comparison of semi-empirical models in
experimental fluid mechanics, wind engineering and flat plate aerodynamics, the effect
of turbulence intensity and integral length scales in different roughness terrains on
the design wind loads on flat plates will be discussed. This is important to provide
accurate estimation of the maximum wind loads on heliostats to avoid structural failure,
but also reduce the cost of over-engineered structural components. The Australian Solar
Thermal Research Institute (ASTRI), led by the University of Adelaide in collaboration
with CSIRO, ANU and DLR, have investigated the static and dynamic wind loads for the
maximum operational and stow survival cases that represent the worst case scenario
loading orientations of a heliostat with respect to the wind. The findings highlight
the importance of accurately reproducing and resolving the critical range of
high-frequency turbulence characteristics through an approach considering the effects
of aerodynamic model scaling of the lower surface layer within the ABL.
Dr Matthew Emes is a University of Adelaide postdoctoral researcher in the School of
Mechanical Engineering, with a background in experimental fluid mechanics, atmospheric
boundary layer turbulence, and a focus on the effects of turbulence on the aerodynamics
and wind loads of heliostats in concentrating solar thermal technology. His research
involves developing innovative techniques for measuring and characterising the temporal
and spatial fluctuations of atmospheric turbulence in wind tunnel and field experiments.
Dr Emes’ research is funded by the Australian Renewable Energy Agency (ARENA), as part
of the Australian Solar Thermal Research Institute (ASTRI) heliostat project.
2020 AFMSS: The National Flying Laboratory Centre – Cranfield University: In-Flight Measurement and Research
Nicholas Lawson
Cranfield University
4.00pm Wednesday 19 August 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
The National Flying Laboratory at Cranfield University operates three aircraft for
research and teaching. The aircraft range from a 7000kg Jetstream 31 turboprop with 19
seats, to two tandem-seat 1000kg aerobatic piston engine aircraft. A Saab340B will
replace the Jetstream in 2021. This presentation will describe the aircraft and their
application in a research environment, with work ranging from the development of fibre
optic pressure and strain sensors in-flight, to the study and validation of an unsteady
DES CFD model, of a stalling Slingsby light aircraft. In the latter case, there is a
focus on using in-flight data to validate the DES model and to study the wake
interaction with the tail plane. In all cases, the challenges of in-flight measurement
will be discussed and the benefit of combining in-flight testing with CFD models.
Professor Nicholas Lawson holds a Chair in Aerodynamics and Airborne Measurement and
heads the National Flying Laboratory Centre at Cranfield University. He is also a
Chartered Engineer, a Fellow of the Royal Aeronautical Society and a member of the
Society of Flight Test Engineers.
Professor Lawson has extensive experience in the development and application of
particle image velocimetry (PIV) and laser Doppler anemometry (LDA) to high speed,
large scale, non-Newtonian and multi-phase flows. Recent work has involved Rolls Royce
plc, Airbus UK, Jaguar Racing and Meggitt, as well as EU partners including DLR and TU
Delft. His current research focus is on the application and development of advanced
instrumentation for airborne and aerodynamic measurement, where fibre optic sensors are
a key focus of his work, in airborne and wind tunnel environments.
He holds a commercial pilots licence with multi-engine piston, instrument and instructor
ratings, a Jetstream 31/32 type rating and is one of the pilots flying for the National
Flying Laboratory Centre.
2020 AFMSS: The fluid mechanics of a large pendulum chain
Geoffrey Vasil
University of Sydney
4.00pm Wednesday 12 August 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
I’ll discuss a particular high-dimensional system that displays subtle behaviour found
in the continuum limit. The only catch is that it formally shouldn’t, which raises a
few questions. When is a discrete system large enough to be called continuous? When
are approximate (broken) symmetries good enough to be treated like the real thing?
When and why does a fluid approximation work as well as we like to assume? What does
all this say about observables and the approach to equilibria? The particular system I
have in mind is a large ideal pendulum chain, and it’s cousin the continuous flexible
string. I propose that this is a perfect model system to study notoriously difficult
phenomena such as vortical turbulence and cascades, but with many fewer degrees of
freedom than a three-dimensional fluid.
Geoff Vasil is a Senior Lecturer in Applied Mathematics at the University of Sydney.
He did his PhD in Atmospheric, Oceanic and Planetary Sciences at the University of
Colorado. After that, he did postdoctoral work in Astronomy Astrophysics at the
University of Toronto and University of California Berkeley. His work focuses on
numerical and high-performance computational methods applied to geophysics and
astrophysical fluid dynamics. He is one of the core developers of the Dedalus project,
which is an open-source community toolkit for solving general partial differential
equations; http://dedalus-project.org.
2020 AFMSS: Predictions in wall-bounded turbulence through recurrent and
convolutional neural networks
Ricardo Vinuesa
KTH
4.00pm Wednesday 05 August 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
The advent of new powerful deep neural networks (DNNs) has fostered their application
in a wide range of research areas, including more recently in fluid mechanics. In this
work we explore the capabilities of DNNs to perform two types of predictions in
turbulent flows: first, we employ recurrent neural networks (RNNs) to perform temporal
predictions of a low-order model of the near-wall cycle of turbulence. Our results
indicate that the RNNs are indeed able to successfully reproduce the dynamics of the
reference database. Second, we will use convolutional neural networks (CNNs) for non
intrusive sensing, i.e. to predict the flow in a turbulent open channel based on
quantities measured at the wall. We show that it is possible to obtain very good flow
predictions, outperforming traditional linear models, and we showcase the potential of
transfer learning between friction Reynolds numbers of 180 and 550. These non
intrusive sensing models will play an important role in applications related to
closed-loop control of wall-bounded turbulence.
Dr. Ricardo Vinuesa is an Associate Professor at the Department of Engineering
Mechanics, at KTH Royal Institute of Technology in Stockholm. He received his PhD in
Mechanical and Aerospace Engineering from the Illinois Institute of Technology in
Chicago. His research combines numerical simulations and data-driven methods to
understand and model complex wall-bounded turbulent flows, such as the boundary layers
developing around wings, obstacles, or the flow through ducted geometries. Dr.
Vinuesa’s research is funded by the Swedish Research Council (VR) and the Swedish e
Science Research Centre (SeRC). He has also received the Göran Gustafsson Award for
Young Researchers.
2020 AFMSS: The challenge of validation in large-scale highly-turbulent
computational fluid dynamics models
Xinqian (Sophia) Leng
University of Bordeaux
4.00pm Wednesday 29 July 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Validation of numerical and Computational Fluid Dynamics (CFD) models are sometimes
not straight forward, and often just absent. Even when validation dataset exists,
whether it is prototype data or experimental measurements, the validation process can
still be complicated, time consuming, and misleading at times, especially for
complicated flow behaviours such as large scale turbulence flows, aerated flows,
unsteady or rapidly-varying flows. In this presentation, I will show a few studies
where numerical (CFD) modelling is used, and validation is needed. The presentation
will show the importance, challenges and compromises of the validation processes. The
goal is to spark thoughts and generate discussions for possible improvements for
future numerical modellers.
Dr. Xinqian (Sophia) Leng’s research interests include physical and numerical (CFD)
modelling of unsteady turbulent flows e.g. breaking waves, bores and positive surges,
field investigations of tidal bores, and hydraulic design of fish-friendly culverts.
Graduated in 2018 with a PhD in Civil Engineering (University of Queensland), she has
authored/co-authored over 30 peer-reviewed publications, including 21 international
journal papers and 16 conference proceedings. Dr. Leng is the recipient of the 2018
Institution of Civil Engineers (UK) Baker Medal, 2019 IdEx Post-doctoral Fellowship
awarded by Université de Bordeaux (France) and is currently working at lab I2M, TREFLE
(SITE ENSCBP), Université de Bordeaux. She was an invited speaker at Sichuan
University International Young Scholars Forum, Water Resource and Hydropower session
(May 2019), Chengdu, China, and an invited speaker for the International Symposium of
Hydraulic Structures, Chile, 2020 (event cancelled due to Covid-19).
2020 AFMSS: What’s in a mean? Towards nonlinear models of wall turbulence
Beverley McKeon
Caltech
4.00pm Wednesday 22 July 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
In this talk I will discuss several approaches to understanding the nonlinear
interactions sustaining turbulence near a wall. Exploiting information embedded in the
turbulent mean field (and how it gets there) using resolvent analysis, emphasis will
be placed on discovering strict rules governing the important scale-to-scale
interactions. First, exact coherent states will be used as a model problem, before the
techniques are extended to turbulent channel flow. A dramatic reduction in complexity
of these problems can be obtained, associated with sparsity, self-similarity and low
rank behavior in the resolvent (attributable to the information encoded in the
turbulent mean field). In this talk, we will synthesize analysis and observations to
distill clues guiding reconstruction of the full nonlinear flow field from the most
amplified spatio-temporal modes, drawing connections with other approaches to related
problems.
The support of the U.S. Air Force Office of Scientific Research under grant FA
9550-16-1-0361 and the U.S. Office of Naval Research under grants N00014-17-1-2307 &
N00014-17-1-3022 is gratefully acknowledged.
Beverley McKeon is Theodore von Karman Professor of Aeronautics at the Graduate
Aerospace Laboratories at Caltech (GALCIT). Her research interests include
interdisciplinary approaches to manipulation of boundary layer flows using morphing
surfaces, fundamental investigations of wall turbulence at high Reynolds number, the
development of resolvent analysis for modeling turbulent flows, and assimilation of
experimental data for efficient low-order flow modeling. She was the recipient of a
Vannevar Bush Faculty Fellowship from the Department of Defense in 2017, the
Presidential Early Career Award (PECASE) in 2009 and an NSF CAREER Award in 2008, and
is a Fellow of the American Physical Society and the American Institute of Aeronautics
and Astronautics. She is the past editor-in-chief of Experimental Thermal and Fluid
Science and currently serves as an associate editor of Physical Review Fluids, as well
as on the editorial boards of the AIAA J., Annual Review of Fluid Mechanics and
Experiments in Fluids. She is the APS representative and Vice Chair of the US National
Committee on Theoretical and Applied Mechanics.
2020 AFMSS: Prediction of inertial particle focusing in curved microfluidic ducts
Yvonne Stokes
University of Adelaide
4.00pm Wednesday 15 July 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Inertial lift and drag forces on particles suspended in flow through a curved
microfluidic duct cause their migration in the cross section of the duct and focusing
by size to different regions of the cross section. This has been used in microfluidic
devices for particle sorting as required for “liquid biopsy”, the isolation of cancer
cells in a routine blood sample. I will discuss a recently developed model to predict
the migration of a spherical particle under the assumption that the particle Reynolds
number is small. This extends an asymptotic model of inertial lift force previously
developed to study inertial migration in straight ducts. Of particular interest is the
existence and location of stable equilibria within the cross-sectional plane.
Depending on its initial position, a particle migrates towards one of these. The
Navier-Stokes equations determine the hydrodynamic forces acting on a particle. A
leading order model of the forces within the cross-sectional plane is obtained through
the use of a rotating coordinate system and a perturbation expansion in the particle
Reynolds number of the disturbance flow. The model is used to predict the behaviour of
neutrally buoyant particles at low flow rates and examine the variation in focusing
position with respect to particle size and bend radius, independent of the flow rate.
In this regime, the lateral focusing position of particles approximately collapses
with respect to a dimensionless parameter dependent on three length scales,
specifically the particle radius, duct height, and duct bend radius. We will consider
ducts with rectangular and trapezoidal shaped cross-sections in order to demonstrate
how changes in the cross-section design influence the dynamics of particles. This is
joint work with Dr Brendan Harding and Prof Andrea Bertozzi.
Yvonne Stokes is an ARC Future Fellow and a Professor in the School of Mathematical
Sciences at The University of Adelaide. She completed her PhD in Applied Mathematics
at The University of Adelaide where she subsequently held an ARC Postdoctoral
Fellowship (2000-2002) before obtaining a tenurable Lecturer position. She is a member
of the Australian Academy of Science National Committee for Mechanical and Engineering
Sciences, and an ANZIAM representative to ICIAM. She has also served on the Executive
Committee of the Women in Mathematics Special Interest Group of the Australian
Mathematical Society.
Yvonne enjoys mathematical modelling, particularly where differential equations are
employed. Her primary research interests are in the field of fluid dynamics, in
particular free-surface and viscous flow problems. One application area of interest is
the drawing of micro-structured optical fibres; another is particle focusing in flows
along curved microfluidic ducts. She is also interested in problems in mathematical
biology, such as nutrient transport and uptake and chemical signalling, with
applications in assisted reproduction technologies.
2020 AFMSS: Wavy drag reduction works!
Wolfgang Schroeder
RWTH Aachen University
4.00pm Wednesday 08 July 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Drag reduction in turbulent boundary layers is key for substantial energy savings in
aerodynamics. Large parts of the flow over the wing of modern aircraft are turbulent
such that even net energy savings of a few percent lead to high cost savings. Active
drag reduction methods have shown to be capable of significantly reducing the drag in
generic external turbulent wall-bounded flows. First, some fundamental knowledge of
the technique of spanwise traveling transversal surface waves will be developed for
the flat plate turbulent boundary flow. These results will also be used to derive via
machine learning a model that allows drag reduction prediction for an extended
parameter range. Based on this input of these generic studies the technique of
spanwise traveling transversal surface waves will be applied to two aerodynamically
completely different wing sections - DRA2303 and NACA4412 - at a chord-based Reynolds
number of Rec = 400,000. Several parameter combinations are tested for
maximum drag reduction and maximum net power saving. The results show a reduction of
the total drag of up to 8.5 percent and a decrease of the viscous drag by up to 12.9
percent. Note that this includes all actuated and non-actuated parts of the surface,
i.e., locally a much higher decrease of the wall-shear stress is achieved.
Additionally the lift is slightly increased and positive net power saving is obtained.
Wolfgang Schröder received his doctorate degree at RWTH Aachen University 1987. After
his postdoc time at the California Institute of Technology in Applied Math, he was in
charge of the Aerothermodynamics Department, Space Infrastructure at the German
Aerospace AG. Then, he joined the University of Applied Sciences in Braunschweig,
before he took over the Chair of Fluid Mechanics and became Head of the Institute of
Aerodynamics of the RWTH Aachen University in 1998. His main research interests are in
the fields of turbulence, aeroacoustics, vortex dynamics, biological and medical
flows, and particle-laden flows. He generally emphasizes a coupled numerical and
experimental approach, i.e., simulations and measurements are used to doublecheck the
findings and to develop innovative theoretical models. Wolfgang Schröder is a Member
of the Academy of Sciences North-Rhine Westphalia and a Membre Titulaire de l'Académie
de l'Air et de l'Espace. He has been Treasurer of EUROMECH from 2004 through 2015.
From 2010 through 2012 he was Dean of the Department of Mechanical Engineering, RWTH
Aachen University and since 2013 he is Member of the Strategy Board of RWTH Aachen
University. In 2013 he received the Carl Friedrich Gauß Preis of the Braunschweig
Society of Sciences.
2020 AFMSS: Cause-and-effect analysis of wall-turbulence theory and applications
Adrián Lozano-Durán
Stanford University
4.00pm Wednesday 01 July 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Even after more than a century, turbulence research is deemed to be in its
infancy by the most critical researchers in the field. And they might be right.
Although we possess a crude practical understanding of turbulence, we still lack a
theory capable of providing the accurate predictions demanded by the industry at an
affordable computational cost. In the present talk, we discuss advancements to
quantify cause-and-effect links in fluid dynamics based on Information Theory. The
approach is used to tackle three important problems in fluid mechanics. In the first
one, we unveil, in a simple manner, that the dynamics of energy-containing eddies at a
given scale is essentially universal and independent of the eddy-size. In the second
problem, we leverage the previous knowledge to forecast turbulent velocity signals via
machine learning. Finally, we show improvements in the aerodynamic efficiency of a
full aircraft in stall at realistic Reynolds number via reduced-order modelling of
active flow
control.
Dr. Adrián Lozano-Durán is currently a Postdoctoral Research Fellow at the Center for
Turbulence Research at Stanford University. He received his PhD in Aerospace
Engineering from the Technical University of Madrid at the Fluid Mechanics Lab advised
by Professor Javier Jiménez. The overarching theme of his research is physics and
modelling of wall-bounded turbulence via simulation, with creativity as a core value.
His work covers a wide range of topics such as turbulence theory and modelling by
machine learning, large-eddy simulation for external aerodynamics, high-speed flows,
and multiphase flows, among others. In January 2021, Adrián will begin his appointment
as an Assistant Professor at the Aerospace Department at MIT.
2020 AFMSS: Optimising geometry and hemodynamics within an arterio-venous fistula
Tracie Barber
University of New South Wales
4.00pm Wednesday 24 June 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Surgically created arteriovenous fistulae (AVF) are used to enable vascular access in
kidney failure patients. The access is used to allow hemodialysis which provides
extracorporeal blood filtration when the kidneys are no longer able to complete this
function. However, complications such as stenosis are very common in AVFs, and access
failure is a costly and life-threatening problem for dialysis patients. These
complications are attributed to hemodynamics perturbations including turbulent flow,
pathophysiological wall shear stress (WSS) and flow recirculation zones. We have used
a novel methodology for generation of patient-specific CFD vasculature models. Models
were generated using an in-house designed 3D freehand ultrasound setup for the vessel
geometry scanning, complemented with spectral Doppler measured ECG-synchronised
flowrates, forming boundary conditions for the CFD solution. Our team works closely
with a local hospital which has allowed the collection of over 100 patient scans,
including a longitudinal study of one patient for 15 weeks.
In the longitudinal study we were able to determine the first results for fistula
maturation, demonstrating that while flow and cross-sectional area increased over time
in the proximal artery and vein, wall shear stress remained fairly constant, while at
a higher than baseline level. Our data has also allowed the effects of different
surgical configurations to be modelled. Earlier work in our group showed that the
traditional AVF geometry, with an acute angle of vein to artery at the juxta
anastomotic region, produced detrimental flow conditions. A ``smooth loop’’ geometry,
when modelled computationally, was seen to result in a more beneficial flow circuit.
This has now been proven surgically, with patients who have the ``smooth loop’’
geometry – often created via the use of a stent during an intervention – performing
better longer term.
In order to create a predictive tool, we have considered a number of flow related
parameters to determine if there is any correlation between these and AVF success
rate. Hemodynamic impedance through the vascular access was calculated by combining
the proximal artery and vein resistances. In one patient case, the first scan featured
low flowrates with stenosis noted in two locations of the outflow vein. The second
scan was taken after the AVF underwent straight stent implantation in the stenotic
region. While greater flowrates results, a new stenosis region formed near the new
stent. A further stenting procedure in the juxta-anastomotic region provided a smooth
loop geometry and removed all stenoses. Oscillatory shear behaviours were seen at
different locations in all scans, localised in regions of low WSS, however impedance
was significantly reduced in the third scan, indicating successful restoration of the
vascular access.
A comparative study of all scans to date shows excellent agreement between low
impedance and AVF success.
Prof. Barber is a UNSW fluid dynamics researcher with a background in ground effect
aerodynamics, and a focus in the last ten years on biomedical applications. Her
research has impact in the fields of fluid dynamics via fundamental understanding
gained, and also in a more applied sense, to direct clinical situations. She works
with both CFD (computational fluid dynamics) and experimental methods, mostly laser
based methods including PIV and LDA. Her group’s interdisciplinary approach takes
engineering technologies and applies them to real world medical problems; this
translational work builds on fundamental findings in flow physics (for example how
turbulence varies spatially and temporally in a pulsatile, stenosed arterial flow) to
apply this insight to real problems (for example, how an over-sized stent causes
turbulence which can then cause re-stenosis). Prof. Barber has over 200 refereed
publications across both biomedical journals (including IEEE Transactions on
Biomedical Engineering, Journal of Controlled Release and Annals of Biomedical
Engineering) and fluid mechanics (including Journal of Fluid Mechanics, Physics of
Fluids and Experiments in Fluids). She is a frequent invited or Keynote speaker at
medical conferences, including 87th Annual Scientific Congress of the Royal
Australasian College of Surgeons, the Symposium of Australia & NZ Society of
Interventional Nephrologists, Verve Symposium, and the Annual Scientific Meeting of
the Renal Society of Australasia.
2020 AFMSS: Linear modelling of turbulent shear flow
Peter Jordan
Institut Pprime
CNRS-Université de Poitiers-ENSMA
4.00pm Wednesday 17 June 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Mean-flow-based (MFB) modelling is increasingly used to study turbulent shear flow,
with applications ranging from low-Reynolds-number, incompressible channel flow to
high-Reynolds-number, compressible jets. The framework, most often cast in resolvent,
or input-output form, holds promise for the improvement of our understanding turbulent
flows, for the elaboration of simplified models and for the conception of
experimentally viable control strategies. The talk will overview four recent
developments. The first concerns an ambiguity associated with the fact that the mean
flow is not a fixed point of the Navier-Stokes equations. This observation illustrates
how results of MFB modelling should be interpreted with caution; it highlights the
importance of carefully considering the non-linear forcing terms implicit in such
models; and it opens up new possibilities for model optimisation. In the second part
of the talk we use the jet-noise example to illustrate how the MFB resolvent framework
can be tailored to explore and model the mechanisms by which turbulent flows drive an
observable of interest. The two final parts of the talk address sensor-based
estimation and control. We propose a resolvent-based linear estimator that can be
constructed for flow systems of large dimension, and which provides optimal linear
estimation for a given set of sensors. We close the presentation with an experimental
demonstration of linear, closed-loop control of stochastic disturbances in a turbulent
jet.
Peter Jordan, born in Cork, Ireland in 1974, is a CNRS Research Director at the
Pprime Institute, Poitiers, France, where he has been since 2001. He holds B.A.,
B.A.I. and Ph.D. degrees in Mechanical Engineering from Trinity College Dublin,
Ireland. His main research interests are in fluid mechanics, with a focus on
aeroacoustics, flow instability and turbulence.
2020 AFMSS: Challenging hydraulic engineering of the 21st century
Hubert Chanson
University of Queensland
4.00pm Wednesday 10 June 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Hydraulic engineering is the science of water in motion and its interactions with the
atmosphere, channel bed and fauna and flora. Current design approaches tend to be
conservative not differing much from ancient designs. Modern designs are often based
upon simplistic steady flow concepts to optimise their performances. Today hydraulic
engineers must embrace new challenges, as water plays a key role in human perception
and is indispensable to all forms of life. The talk will raise questions about current
hydraulic design practices, too often based upon the simplistic assumptions of steady
monophase Newtonian flow situations and optimised for a design discharge. During the
seminar, the speaker discusses these challenges in terms of self-aeration processes at
hydraulic structures and upstream fish passage in culverts. It is argued that a number
of technical solutions are not satisfactory, e.g. in terms of aquatic fauna, fluid
structure interactions and operational restrictions.
Altogether, the technical challenges in hydraulic engineering and design are gigantic
for the 21st century hydraulic engineers. The speaker aims to share his passion for
hydraulic engineering, as well as share some advice for early-career academics and
researchers.
Hubert Chanson is Professor of Civil Engineering at the University of Queensland,
where he has been since 1990, having previously enjoyed an industrial career for six
years. His main field of expertise is environmental fluid mechanics and hydraulic
engineering, both in terms of theoretical fundamentals, physical and numerical
modelling. He leads a group of 5-10 researchers, largely targeting flows around
hydraulic structures, two-phase (gas-liquid and solid-liquid) free-surface flows,
turbulence in steady and unsteady open channel flows, using computation, lab-scale
experiments, field work and analysis. He has published over 1,000 peer reviewed
publications. He serves on the editorial boards of International Journal of Multiphase
Flow, Flow Measurement and Instrumentation, and Environmental Fluid Mechanics, the
latter of which he is currently a senior Editor. He co-chairs the Organisation of the
22nd Australasian Fluid Mechanics Conference to be held in Brisbane, Australia
2020 AFMSS: Ensemble Kalman filter estimation of heat transfer parameters in a coupled
climate model
Vassili Kitsios
Monash University
4.00pm Wednesday 3 June 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
General circulation models (GCM) are unable to explicitly capture all of the scales of
motion present in the climate system, ranging from millimetres to hundreds of
thousands of kilometres. One, therefore, resorts to parameterising the influence of
the unresolved small scale processes. Many of these parameters are known with little
precision, which is one of the main contributors to model bias and limited
predictability. The adopted GCM is a coupled atmospheric, oceanic, and sea-ice climate
model with approximately 100 million degrees of freedom. Using an ensemble Kalman
filter (EnKF) we develop a systematic and objective means of determining the model
initial states and spatio-temporally varying parameters that minimise the difference
between a 96 member ensemble of short term model forecasts and a network of real world
observations of the Earth system. The parameters of interest are those governing the
heat transfer between the atmosphere and ocean. The estimated parameter maps resemble
known model biases, and are shown to improve model skill in the in-sample DA
experiments, and in out-of-sample multi-year climate forecasts.
Dr Kitsios completed a PhD with the University of Melbourne and the Université de
Poitiers on fluid dynamical stability and model reduction (2006-2010). He then
undertook post-doctoral research with the CSIRO Oceans and Atmosphere (O&A) division
(2010-2013) and the Monash University Laboratory for Turbulence Research in Aerospace
and Combustion (2013-2016), on the numerical simulation and parameterisation of
atmospheric, oceanic and boundary layer flows. He then held an industrial research
position at a hedge fund (2016-2017) developing trading algorithms on the basis of
macroeconomic themes and market conditions. Since rejoining CSIRO O&A in 2017, he has
been undertaking research on the: parameterisation, data assimilation and ensemble
initialisation methods for decadal climate prediction; and quantification of the
influence of climate variability and change on socio-economic indicators.
2020 AFMSS: Fluid-Structure Interaction Problems in Aerospace Applications
Gareth Vio
University of Sydney
4.00pm Thursday 28 May 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Fluids Structure Interaction problems arise in aeronautical application in different
forms. This talk will introduce a number of areas of interest, namely shockwave
boundary layer interaction, cavity flow as well as its application topology
optimisation problems. The talk will touch on problem of parallelisation of CFD codes
for FSI problems as well as converge issue in Topology optimisation problems. I will
conclude with a summary of some challenges and future opportunities.
Gareth A. Vio received his bachelor's degree in aerospace engineering, and PhD
degree in Aeronautical Engineering from The University of Manchester in 1999 and 2005
respectively. He was a postdoctoral researcher at The University of Manchester and
Liverpool in the UK, working on non-linear prediction problems, aeroelastic tailoring
and system identification.
He is currently a Senior Lecturer with the School of Aerospace, Mechanical and
Mechatronic Engineering at The University of Sydney. His research interests include
multidisciplinary design and topology optimisation, shock wave/boundary layer
interaction, nonlinear structural dynamics and energy harvesting.
2020 AFMSS: Recent progress in experimental two-phase flows
Agisilaos Kourmatzis
University of Sydney
4.00pm Wednesday 20 May 2020
Online Event (2020 Australasian Fluid Mechanics Seminar Series)
Two-phase flows surround us. Understanding their behaviour and being able to control
them, is critical for a multitude of applications, ranging from fuel injector design,
to agricultural technologies and pharmaceutical aerosols. The aim of today's talk is
to initially provide a general overview of some of the recent two-phase flows research
in the group, and then delve into a bit of detail into 2 key areas of ongoing
research. The first area being turbulent atomization and the role of instabilities,
and the second area being pharmaceutical powder based flows. I will conclude with a
summary of key findings and where some challenges and future opportunities are.
Dr. Kourmatzis graduated with a PhD in Fluid Dynamics from the University of
Southampton, UK (2011) after completing Bachelors and Masters degrees in Mechanical
Engineering from the University of Nottingham and Imperial College London
respectively. He was a postdoctoral research associate at the University of Sydney
from 2011-2015. He held an academic position at Macquarie University from 2015-2017,
helping to pioneer the new mechanical engineering program there, prior to re-joining
USyd in 2017 as a lecturer. His research interests lie in two-phase flows (aerosols
sprays/powders), turbulence, and laser diagnostics. He engages with fundamental
science in these areas but also with a number of applications ranging from turbulent
spray combustion and fire suppression, to drug delivery to the lungs or brain. He has
published more than 40 international peer reviewed journal articles in this area, and
has attracted more than ~2m $ of external funding in the last 3 years from the ARC and
other sources.
Attached eddy model revisited with quasilinear approximation*
Yongyun Hwang
Imperial College London
3.30pm Friday 13 March 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Townsend’s model of attached eddies for boundary layers is revisited with a
quasi-linear approximation. The velocity field is decomposed into a mean
profile and fluctuations. While the mean is obtained from the nonlinear
equations, the fluctuations are modelled by replacing the nonlinear
self-interaction terms with an eddy-viscosity-based turbulent diffusion and
a stochastic forcing. The colour and amplitude of the stochastic forcing are
then determined self-consistently by solving an optimisation problem which
minimises the difference between the Reynolds shear stresses from the mean
and fluctuation equations. When applied to turbulent channel flow in a range
of friction Reynolds number from Reτ = 500 to Reτ =
20000, the resulting
turbulence intensity profile and energy spectra exhibit exactly the same
qualitative behaviour as DNS data throughout the entire wall-normal location,
while reproducing the early theoretical predictions of Townsend and Perry
within a controlled approximation to the Navier-Stokes equations. Finally,
the proposed quasi-linear approximation suggests that the peak streamwise and
spanwise turbulence intensities may deviate slightly from the logarithmic
scaling with Reynolds number for Reτ > 10000.
*This is joint work with Bruno Eckhardt who sadly passed away recently.
Yongyun Hwang is a senior lecturer in the Department of Aeronautics at Imperial
College London. He received his PhD in the Hydrodynamics Laboratory (LadHyX)
at Ecole Polytechnique in 2010. After spending one and half years at the same
institution as a post-doctoral researcher, he moved to the Department of
Applied Mathematics and Theoretical Physics (DAMTP) at University of Cambridge
as a Marie Curie post-doctoral research fellow to study pattern formations in
active fluids in 2012. He joined Imperial College London in October 2013. His
research interests are broadly defined in theoretical and computational fluid
dynamics, and he specialises instabilities, coherent structures, turbulence
and pattern formations in physical and biological systems.
Bifurcation of periodic flows around flapping bodies
Olivier Marquet
ONERA
3.30pm Tuesday 10 March 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Two-dimensional flows induced by flapping rigid bodies may exhibit surprising
dynamical behaviors that are simply obtained by unsteady numerical simulations
of the fluid-solid interaction. During that talk, we will first illustrate
several interesting states arising in three configurations widely investigated
in the last decade: (i) the time-averaged deviation of the periodic vortex-street
generated in the wake of a wing with a prescribed harmonic pitching motion, (ii)
the synchronization (or not) of a spring-mounted cylinder with the vortex-shedding
in its wake and (iii) the coherent or back-and-forth self-propulsion of flapping
plates in an initially quiescent flow. In the second part of this talk, we will
show that, for all of these cases, the occurrence of these states can be explained
as bifurcations of periodic solutions of the governing equations. To that aim, I
will introduce two methods allowing the numerical computation of unstable periodic
solutions. The symmetry-preserving method, based on time-marching simulations,
has been used to compute unstable periodic solutions with (iii) spatial or (i)
spatio-temporal symmetries, while the more general harmonic balance method solve
for periodic solutions in the frequency domain. Using Floquet analysis to determine
the stability of those periodic solutions, we can then obtain bifurcation diagrams
that I will finally use to better understand (ii) the lock-in phenomenon in vortex
induced vibrations and (iii) the existence of coherent and back-and forth oscillating
state for self-propelled flapping plate.
In 2003, Olivier received an engineering degree from Ecole Nationale Supérieure
de Technique Avancées (ENSTA, France) and a master degree in mechanical engineering,
speciality in fluid mechanics, from University Pierre & Marie Curie (UPMC, France).
In October 2003, he received a PhD grant from the Direction Générale de l’Armement
(DGA) and started a doctoral thesis at the Fundamental and Experimental Aerodynamics
Department (DAFE) of ONERA. In December 2007, he received a doctoral degree from the
University of Poitiers for his work on the Global stability and control of
recirculating flows. In January 2008, he obtained a Junior Research Fellowship
from DGA and started a one-year postdoctoral project at the Universität der
Bundeswehr in Munich (Germany). In 2009, he came back to France for a one-year
post-doctoral project on the optimal forcing of boundary layer instabilities, at
Laboratoire d'Hydrodynamique (LadHyx) from Ecole Polytechnique and ONERA-DAFE. In
January 2010, he got a permanent position as research engineer within the Fluid
Mechanics Unit (MFLU) of ONERA-DAFE. In March 2015, he received a Starting Grant
from the Eurpeoan Research Council for the project AEROFLEX, AEROelastic instabilities
and control of FLEXible structures. In 2016, he became Maitre de Recherche at ONERA
and member of the scientific council for the Energetic and Fluid Mechanics branch.
Since January 2018, he is a senior research scientist in the Metrology,
Assimilation and Flow Physics Unit (MAPE for Metrologie, Assimilation et Physique
des Ecoulements) of the ONERA Aerodynamics, Aeroelasticity and Acoustics Department
(DAAA).
Three-dimensional boundary layers with short spanwise scales
Peter Duck
University of Manchester
4.00pm Friday 6 March 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
We consider three-dimensional boundary-layer flows, where the spanwise scale is
comparable to that of the boundary-layer thickness. To place this three-dimensional
formulation into a specific context, we consider a semi-infinite flat plate aligned with
an oncoming incompressible, uniform flow of speed U
*∞. An arbitrary choice of reference length scale,
L
*, allows for a non-dimensional Cartesian coordinate system (L
*
x,L
*y,L
*z) aligned with the leading edge of the plate at
x=0, such that y=0, x>0 defines the plate surface. To capture short spanwise scales
typical of streaks we rescale in the (y,z) plane according to (Y,Z) = Re
1/2
(y,z). Here Re=U
*∞
L
*ν
* (for kinematic viscosity ν
*) is a
global Reynolds number based on the chosen length scale. The corresponding high Reynolds
number flow field (assumed to be steady) is
with pressure
For large Reynolds number the solution is therefore governed by
This system is often referred to as the
boundary-region equations.
This system encompasses much of the full flow physics, and is applicable to a wide
variety of flow configurations, including corner boundary layers, spanwise-periodically
disturbed flows with links to transient growth and streaks. We first consider steady
three-dimensional states driven by a finite-width slot aligned with the flow direction
and self-similar in their downstream development. The classical two-dimensional states
are known to only exist up to a critical ('blow off') injection amplitude, but the
three-dimensional solutions here appear possible for any injection velocity. We then go
on to consider both the formation and stability of isolated streak structures embedded
in a Blasius boundary layer, triggered by injection of fluid through the surface of the
plate. Finally we consider the far downstream behaviour of (small amplitude) unsteady
disturbances to Blasius boundary layers. We discuss the two disparate structures
that have been proposed for two-dimensional (eigen-) disturbances, the first due to Lam
& Rott (1960) and Ackerberg & Phillips (1972) and the second due to Brown &
Stewartson (1973).
Peter Duck is a Professor of Applied Mathematics at the University of Manchester. He
received his BSc in Aeronautics and his Ph.D. from the University of Southampton and
went on to do post-docs at Imperial College London in Mathematics and Ohio State
University in Aeronautics. In 1979, he moved to the University of Manchester where he
has served as the Head of Department and School of Mathematics. His research interests
in fluid mechanics include asymptotic methods, boundary-layer flows, separated flows,
and linear and nonlinear instabilities. He is currently the Executive Editor of the
Quarterly Journal of Mechanics and Applied Mathematics and an Associate Editor of
Theoretical and Computational Fluid Dynamics. Additionally, he has supervised over 40
research students and authored over 140 scientific articles.
Recent developments in zonal Hybrid RANS LES methods for industrial applications
Alistair Revell
University of Manchester
3.30pm Friday 28 February 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
In my talk I will present an overview of recent developments in turbulence
modelling and simulation where scale-resolution is sought at reduced cost.
Hybrid RANS-LES methods are first introduced and discussed in general, and
the importance of the RANS model is highlighted. In this context I will show
that zonal methods are a versatile tool, providing efficient approximation
of fluctuations in order to move from time-averaged to instantaneous
treatment. Code-code coupling approaches are presented, deploying multiple
instances to simultaneously solve separate RANS and LES domains, interlinked
via volume source terms. I will then present details of a similar approach
which instead uses the lattice Boltzmann method accelerated on GPU devices
as the time-resolving component, coupled to a RANS finite volume method solver
running on CPU; with some reflections on the opportunities this provides.
Alistair graduated from UMIST with an MEng degree in Aerospace Engineering with
French, including time at ENSMA, Poitiers. He was again based in Manchester for
his PhD in Turbulence Modelling, including a year at IMFT, Toulouse and shorter
placements at Electricité de France (EdF), Paris and Stanford CTR. He became a
Lecturer at Manchester in 2007, initially focussed on the development of
Code_Saturne in collaboration with EdF. In 2011 he undertook a research
sabbatical in Madrid to work on fluid-structure interaction and the lattice
Boltzmann method. In 2017 he became Reader and Deputy Head of Department of
Mechanical, Aerospace & Civil Engineering and is also Head of Social
Responsibility. He leads a research group working on the development of CFD
methods for turbulent flow and fluid-structure interaction.
Calculation of the mean velocity profile for strongly turbulent Taylor–Couette flow and arbitrary radius ratios
Pieter Berghout
University of Twente
3.30pm Friday 21 February 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Taylor–Couette (TC) flow is the shear-driven flow between two coaxial
independently rotating cylinders. In recent years, high-fidelity simulations
and experiments revealed the shape of the streamwise and angular velocity
profiles up to very high Reynolds numbers. However, due to curvature effects,
so far no theory has been able to correctly describe the turbulent streamwise
velocity profile for all radius ratios, as the classical Prandtl–von Kármán
logarithmic law for turbulent boundary layers (BLs) over a flat surface at
most fits in a limited spatial region.
Here we address this deficiency by applying the idea of a Monin–Obukhov
curvature length to turbulent TC flow. This length separates the flow regions
where the production of turbulent kinetic energy is governed either by pure
shear from that where it acts in combination with the curvature of the
streamlines. We demonstrate that for all Reynolds numbers and radius ratios,
the mean streamwise and angular velocity profiles collapse according to this
separation. We then derive the functional form of the velocity profile.
Finally, we match the newly derived angular velocity profile with the constant
angular momentum profile at the height of the boundary layer, to obtain the
dependence of the torque on the Reynolds number, or, in other words, of the
generalized Nusselt number (i.e., the dimensionless angular velocity transport)
on the Taylor number.
Pieter graduated as a Chemical Engineer from Delft University of Technology
in 2015. His thesis was on the Lattice Boltzmann modelling of surfactant
laden droplets, and continued this research for another year as a research
assistant at the University of Limerick, Ireland. In 2017, he started his PhD
at the Physics of Fluids group at the University of Twente under Detlef Lohse,
working on various topics in turbulent Taylor-Couette flow.
The effect of heat transfer on turbine performance
Lachlan Jardine
Whittle Lab, University of Cambridge
3.30pm Friday 7 February 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
For over 60 years, gas turbines have bled air from the compressor to cool
blades in the high-pressure turbine. The cooling air is used to protect
these turbine blades, allowing them to operate at temperatures several
hundred degrees above their melting point. It is therefore surprising that
little is understood about the effect of heat transfer on turbine efficiency.
There is not even a consensus on how to define the efficiency of a cooled
turbine. This talk seeks to demonstrate a thermodynamic method capable of
linking different levels of design, rigorously defining turbine performance
and agreeing with industrial experience.
Lachlan has recently submitted his PhD thesis at the Whittle Laboratory,
University of Cambridge, which investigates the impact of cooling on gas
turbine performance. He has successfully obtained a Knowledge Transfer
Fellowship, in partnership with Rolls-Royce, to continue developing this
research. More broadly, Lachlan is particularly interested in the fields
of heat transfer, computational fluid dynamics and turbulence.
Some Roots to Our Uncertainty Regarding Values of von Kármán Constants
Vorticity fluxes: A tool for three-dimensional secondary flows in turbulent
Shear flows
Hassan Nagib
Illinois Institute of Technology
3.30pm Thursday 6 February 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Nonlinear optimisation of transition in pipe flow
Ashley Willis
University of Sheffield
3.00pm Tuesday 4 February 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Turbulence and laminar flow can coexist at the same flow rate in pipe-,
Couette- and channel-flows. Starting from each of the two states, two
nonlinear optimisation problems can be asked: "What is the minimal
disturbance to laminar flow that causes transition to turbulence?" and
"What is the minimal (body) force that can 'destabilise' turbulence towards
relaminarisation?". In particular, this latter problem is motivated by
surprising experiments showing that a partial blockage in a pipe can actually
lead to relaminarisation, rather than just stirring up more turbulence
(Kühnen et al. 2018, Nature Physics 14, 386). The two questions can be
formulated as similar nonlinear variational problems, in principle. Several
issues arise in practice, but optimal perturbations and forces of consistent
structure can nevertheless be determined.
Ashley Willis completed his PhD at Newcastle University, U.K, on flows
related to the magnetic stability of accretion discs. He studied the
geodynamo in Leeds before moving to Bristol to work on fundamental fluid
mechanics. He went on to a Marie Curie fellowship at LadHyX, Ecole
Polytechnique near Paris, before settling in Sheffield.
Wall-bounded stratified turbulence
Francesco Zonta
TU Wien
3.30pm Tuesday 17 December 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
In this talk, I will focus on the problem of stratified flows in
wall-bounded turbulence. In the first part of the talk, I will consider the
case of thermally-stratified flows. The interaction between turbulence and
thermal stratification induces remarkable modifications on the flow field,
which in turn influences the overall transfer rates of mass, momentum and
heat. The discussion will spin around recent results obtained by a
systematic campaign of Direct Numerical Simulations of stratified turbulence
at large Reynolds number. In the second part of the talk, I will consider
the case of viscosity-stratified flows. I will focus on a lubricated
channel (i.e. a flow configuration in which an interface separates a thin
layer of a less-viscous fluid from a main layer of a more-viscous fluid
flowing inside a plane channel), and I will discuss the influence of
viscosity and surface tension on the overall friction (drag reduction
mechanism).
Dr. Francesco Zonta graduated in Mechanical Engineering in 2006 at the
University of Udine, where he also completed his PhD in 2010. From 2010 to
2016 he has been Research Assistant at the University of Udine and at the
University of Torino. In 2014, he has been invited scholar at the University
Pierre et Marie Curie (UPMC, Paris). Since 2016, he is Senior University
assistant at the Institute of Fluid Mechanics and Heat Transfer of the
Vienna University of Technology. His research focuses on turbulence, heat
transfer, multiphase flows and computational fluid dynamics. He has obtained
a number of grants for HPC (High Performance Computing) applications, and he
has been the recipient of "Ermanno Grinzato" prize awarded by AIPT
(2013).
Vortex structure over cubical block array
Naoki Ikegaya
Kyushu University
3.30pm Tuesday 10 December 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The momentum and scalar transports from an urban surface into an atmosphere
is one of the important factors to determine environment in the urban area.
The geometric dependency of macroscopic aerodynamic parameters such as the
transfer coefficients for momentum and scalar has been revealed by a series
of wind-tunnel experiments. However, it is not well known that the features
of locally generated turbulent flow structures due to the ejection event,
strong upward transport of low-speed momentum fluid, and the sweep event,
strong downward transport of high-speed momentum fluid for the urban-like
boundary layer. Therefore, we performed numerical simulation using
Large-eddy simulation model over urban-like surfaces consisted of cubical
blocks. The quadrant analysis for instantaneous flow field is conducted to
investigate the contribution of ejection or sweep to the total momentum
transport over cubical arrays. In addition, the conditional averaged flow
fields show that the ejection or sweep event can be generated by the
pair-vortex probably corresponding to the leg structures of hair-pin vortex,
resulting in the strong upward or downward flow.
Dr Naoki Ikegaya is an Assistant Professor in Faculty of Engineering
Sciences, Kyushu University, Japan. He received his Doctorate degree of
Engineering from Kyushu University in 2011. His major is architectural
environmental engineering and wind engineering by means of both wind-tunnel
experiment and computational fluid dynamics approach. He focuses on
transport phenomena occurring in the turbulent urban boundary layer where
various rigid buildings work as roughness to generate complex and
non-uniform turbulent flows within the urban canopy layer. He is currently
a Visiting Scientists in Ocean and Atmosphere, Commonwealth Scientific and
Industrial Research Organisation (CSIRO) to work with Prof. J.J. Finnigan on
the turbulent statistics scaling over various vegetation and urban canopies.
Drag-reduction using compliant coatings: Learning from the Dolphin?
Tony Lucey
Curtin University
3.30pm Friday 6 December 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Reducing the drag, and thus the propulsive power requirement, of any vehicle
is highly desirable in an age of environmental concerns and inexorably
increasing fuel costs. Nature has been 'working' on such challenges for
millions of years through the process of evolution; the 'design' of the
dolphin is an outstanding example of its success in marine locomotion. One
facet of its hydrodynamic optimisation appears to arise from the structure
of its skin that dynamically interacts with the flow of water past it when
the dolphin is in motion.
This presentation will tell the story of research on compliant coatings, an
artificial rubber-based equivalent of the dolphin's skin, that attempt to
confer similar hydrodynamic advantages when applied to an otherwise rigid
wetted surface. In particular it will focus on the research evidence that
compliant coatings are able to postpone the transition from laminar to
turbulent flow in the boundary layer, thereby reducing skin-friction drag.
In fact, there is, at least theoretically, the possibility of postponing the
onset of turbulence indefinitely to reach the 'Holy Grail' of low-drag
design. There is also evidence that compliant coatings can reduce turbulent
skin-friction although the underlying mechanisms for this are not yet well
understood. More broadly, the presentation will serve as a case study of the
sometimes tortuous path of research from scientific observation to
understanding of fundamental physical phenomena and from there to future
technologies.
Tony Lucey is a John Curtin Distinguished Professor, twice former Dean of
Engineering (2005–2008, 2015–2018), and former (2009–2019)
Head of the School of Civil and Mechanical Engineering at Curtin University.
He took his Bachelor and PhD degrees at the Universities of Cambridge and
Exeter in the UK. He has held positions at the Universities of Exeter and
Warwick in the UK and the Asian University of Science and Technology in
Thailand. He gained industrial experience as an aerodynamicist at British
Aerospace PLC in the UK. He is recognised for his fundamental research in
fluid-structure interaction and its applications in engineering and
biomechanics. He also publishes in the areas of engineering education and
appropriate technology. His career has been punctuated by spells working in,
or for, developing countries. He is active in the peak professional body
Engineers Australia (EA): this has included being the 2010 WA Division
President and regularly chairing EA panels for the accreditation of
Engineering degrees at Australian universities (including Melbourne!). He
has served on the ARC College (2012–2014) and its Selection Advisory
Committee (2019). He was Secretary of the Australasian Fluid Mechanics
Society from its inception in 2009 and in 2019 became President of the
Society.
Barnacle fouling and its effect on near-wall turbulence
Angela Busse
University of Glasgow
3.30pm Wednesday 4 December 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Marine biofouling has impacted seafaring since ancient times by decreasing
the maximum range and speed of watercraft. As marine organisms accumulate
on a ship, the skin-friction drag of the hull rises significantly, leading
to higher fuel burn and associated emissions. The form of biofouling with
the most severe impact on the shipping industry is calcareous macrofouling
which is caused by organisms protected by a calcareous outer shell, such as
barnacles, tubeworms, and mussels.
This presentation will focus on the impact of barnacle-type roughness on
wall-bounded turbulence. The rough surfaces under consideration have been
generated with an algorithm that mimics the settlement behaviour of
barnacles. Direct numerical simulations are used to quantify the effects of
different topographical parameters such surface coverage and clustering on
near-wall turbulence statistics.
Barnacle-type roughness can be interpreted as an 'hybrid' form of roughness
that combines both features of irregular multi-scale roughness and
traditional regular rough surfaces built from roughness elements. It
therefore serves as an interesting test case for the commonalities and
dissimilarities of the fluid dynamic effects of regular versus irregular
forms of surface roughness.
Dr Angela Busse is a lecturer in the James Watt School of Engineering at
the University of Glasgow. Her main research area is the effect of rough
and superhydrophobic surfaces on wall-bounded turbulence. Her further
research interests include Lagrangian statistics of turbulence,
magnetohydrodynamic turbulence, flows past bluff bodies, and the
aerodynamics of plants.
Studies on complex flows with tomographic PIV
Qi Gao
Zhejiang University
3.30pm Friday 18 October 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Tomographic particle image velocimetry (TPIV) proposed by Elsinga
et al. (2006) has become a powerful experimental technique to
measure a three-dimensional three-components (3D3C) velocity field. With
high-frequent sampling, time-resolved TPIV can further achieve pressure
reconstruction at the same time with volumetric velocity measurement.
Therefore, this technique is widely used for studying complex flows. In this
talk, several classical flows based on TPIV measurement will be briefly
presented. A flow passing a hemisphere in laminar boundary layer is highly
associated with transition. With time-resolved TPIV, both velocity and
pressure fields are measured to see the revolution of the induced standing
vortices and hairpin vortices. For a turbulent boundary layer (TBL) flow,
dominant vortex structures in near-wall region are statistically
investigated. Methods of linear stochastic estimation (LSE), proper
orthogonal decomposition (POD) and pre-multiplied energy spectra are
utilized for studying coherent flow structures regarding scales, amplitude
and frequency modulation effects on the inner–outer interactions of
TBL. A point-swirl model is being developed for eddy modeling. There are
several ongoing projects on TPIV measurements of live fish
swimming, critical cavitation of tip vortex, laser induced cavitation,
homogeneous isotropic turbulence (HIT) generated with a turbulent box and
breakdown of leading vortices of a delta wing. Meanwhile, a series of
post-processing methods are proposed for better noised reduction, error
elimination and missing data fixing based on physical constraints from
continuity, momentum and irrotational equations.
Dr Qi Gao received his bachelor degree from Zhejiang University in 2001,
his master degree from Tsinghua University in 2005, and his Ph.D. from the
University of Minnesota in 2011. He joined the Beijing University of
Aeronautics and Astronautics as an assistant professor in 2011, and was
promoted to associate professor in 2013. He moved to Zhejiang University in
2018. Currently, he is an associate professor at the School of Aeronautics
and Astronautics, Zhejiang University, China and serves as the Director of
Laboratory of Fluid Mechanics at the Institute of Fluid Engineering.
Dr. Gao's research is broadly in the area of experimental fluid mechanics.
Current projects are focused on developing techniques of volumetric
velocimetry and their applications. Studies on turbulent boundary layers,
cardiovascular flows, compressible flows and flow control are areas of high
interest. He has published about 30 research articles and applied for
over 40 patents (10 have been certified). Dr. Gao received the Chinese
National Award of Technology Invention (second class) in 2018.
3D Lagrangian particle tracking with Shake-The-Box
Peter Manovski
University of Melbourne
3.30pm Friday 4 October 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
This talk will focus on two test campaigns conducted at the German Aerospace
Centre (DLR) using the new Lagrangian Particle Tracking algorithm
Shake-The-Box (STB). Firstly, time-resolved STB was applied to a low speed
impinging jet flow. Helium-filled soap bubbles were used as tracer
particles, illuminated with pulsed LED arrays and captured with six high
speed cameras. A large measurement volume (54 L), captured up to 180,000
particle tracks for a jet velocity of 4 m/s. Reconstructed instantaneous
volumetric pressure fields were obtained and validated against microphone
recordings at the wall. The second test used multi-pulse STB to measure the
subsonic jet flow at Mach 0.85. Using two imaging systems each with four
cameras and four lasers, up to 50,000 tracks of four-pulse sequences were
captured, enabling high resolution instantaneous and 3D flow fields of
velocity and material acceleration. For the first time, this revealed 3D
acceleration and fluctuation fields, as well as PDF statistics.
Bin-averaging of the particle tracks provided sub-pixel (0.75 px) resolution
statistical quantities that were able to resolve the extremely steep
velocity gradients in the jet shear layer. In the final component of the
talk I will provide a brief outlook of my intended PhD research studies at
The University of Melbourne.
Peter Manovski graduated from Monash University in 2005 completing a double
degree in Bachelor of Engineering (Mechanical) and Bachelor of Technology
(Aerospace) with First Class Honours. The following year he obtained
employment with Defence Science and Technology (DST) Group Melbourne.
Working in the field of Experimental Aerodynamics for over 14 years, he has
gained significant knowledge and experience in both low speed and transonic
wind tunnel test techniques. He leads a small team working in the DST wind
tunnels that is responsible for planning, conducting, analysing and
reporting of aerodynamic experiments in support of Defence S&T programs
and fundamental research initiatives across the Aerospace and Maritime
domains. In 2016, he was awarded a DST International Fellowship and was
posted at the German Aerospace Centre (DLR) for 14 months.
Recently he commenced a work-based PhD (part-time) at The University of
Melbourne with the aim of characterising the acoustic performance of UAS
with the application of synchronised volumetric flow field and acoustic
measurements.
Friction and fluctuations in transitional pipe flow
Rory Cerbus
Okinawa Institute of Science and Technology
3.30pm Tuesday 24 September 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Pipe flow is laminar at low flow velocities and turbulent at high flow
velocities. At intermediate velocities there is a transition wherein plugs
of laminar flow alternate along the pipe with "flashes" of a type of
fluctuating, non-laminar flow which continue to be the object of intense
study. Here we address two properties of flashes: friction and fluctuations.
In the 19th century, Osborne Reynolds, who first reported flashes, sought to
connect them with quantitative "laws of resistance" whereby the fluid
friction is determined as a function of the Reynolds number. While he
succeeded for laminar and turbulent flows, the laws for transitional flows
eluded him and remain unknown to this day. In seemingly unrelated work,
A.N. Kolmogorov predicted that all turbulent flows are the same at small
scales: the property of 'small-scale universality'. Based on the restrictive
assumptions invoked by Kolmogorov to demonstrate this universality, it is
widely thought that only idealized turbulent flows conform to this
framework. Using experiments and simulations that span a wide range of
Reynolds number and by properly distinguishing between flashes and laminar
plugs in the transitional regime, we uncover the law of resistance for
flashes and demonstrate for the first time that small-scale universality
holds even in low Reynolds number, inhomogeneous, unsteady transitional pipe
flow.
Rory is a Staff Scientist in Pinaki Chakraborty's Fluid Mechanics Unit at
the Okinawa Institute of Science and Technology (OIST) in Okinawa, Japan.
Rory received his Ph.D. in Physics in 2014 from the University of Pittsburgh
experimentally studying two-dimensional turbulence under the direction of
Walter Goldburg. At OIST, Rory has continued working on two-dimensional
turbulence but mainly focuses on experiments and simulations of transitional
pipe flow. In January 2020, Rory will move to the Université de
Bordeaux in France to work with Hamid Kellay on granular flows under a
Marie Skłodowska-Curie Fellowship.
Replacing the heart with a mechanical pump
Shaun Gregory
Monash University
3.30pm Friday 20 September 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Heart failure is an expanding global health issue while the gold-standard
treatment, heart transplant, is limited by low organ donation numbers.
Mechanical solutions to bridge patients to transplant or as a destination
therapy come in the form of rotary blood pumps which use magnetically
suspended and rotated impellers to take over the native heart's
blood-pumping function. These devices are prone to complications such as
bleeding, clotting, infection and an inability to change performance based
on changes in patient activity. Collaborative research between Monash
University, the Alfred Hospital, and the Baker Heart and Diabetes Institute
aims to solve these issues by forming a close collaboration between
engineers, biological scientists, clinicians and patients. This presentation
will summarise the key research projects underway through this collaboration
including the development of new devices, evaluation of blood flow dynamics,
reducing infection through electro-writing, physiological control systems,
and more.
Dr Shaun Gregory is a senior lecturer in the department of Mechanical and
Aerospace Engineering at Monash University, a Heart Foundation Future Leader
Fellow, and an Honorary Research Fellow in the Baker Heart and Diabetes
Institute. He holds a PhD in medical engineering from Queensland University
of Technology, and has completed research fellowships at the University of
Queensland and Griffith University. Shaun's research interests centre around
cardiovascular engineering, with a specific focus on the development and
evaluation of mechanical circulatory and respiratory support systems
(artificial hearts and lungs). Shaun directs a cardiovascular engineering
research laboratory in the Baker Heart and Diabetes Institute where
engineers, clinicians and biological scientists work side-by-side at the
bench to develop novel solutions to clinically-relevant problems.
Global linear stability theory in aerospace applications
Vassilios Theofilis
University of Liverpool
3pm Wednesday 18 September 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Global linear stability theory is the natural extension of the classic local
analysis in flows with multiple inhomogeneous spatial directions. The
lecture will provide an overview of highlights of laminar-turbulent
transition research based on linear theory, from its early development in
Göttingen by Prandtl himself, Tollmien, Schlichting, Görtler and
others, up to the present-day theoretical developments, natural laminar
flow wing wind-tunnel experiments and flight tests. Subsequently, successes
of global linear theory will be highlighted in a number of external and
internal aerospace applications in the incompressible limit, including the
swept leading edge boundary layer at the windward face of an aircraft wing;
global modes (and stall-cell formation) on spanwise homogeneous and
three-dimensional wings; centrifugal instabilities in two- and
three-dimensional open cavities and in rotating cavities of the High
Pressure Turbine of an aircraft engine. In a supersonic boundary layer,
PSE-3D transition prediction in the wake of an isolated roughness element
will be discussed, while instability and transition prediction in two
hypersonic flows will be highlighted: an elliptic cone modelling Ma=7 flight
of the HIFiRE-5 research vehicle and shock/laminar boundary layer
interaction on a double cone at Ma=15. It will be argued that improved
understanding of flow instability in geometrically complex configurations,
especially in the high speed regime, is expected to deliver physics-based
flow control methodologies that will aid the development of next-generation
flight vehicles in the first half of this century.
Loss analysis of axial compressor cascades
Jake Leggett
University of Melbourne
3.30pm Friday 13 September 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The prediction of an axial compressor's loss early on in the design phase
is a valuable and important part of the design process. The work presented
here focuses on assessing the accuracy of current prediction methods,
Reynolds Averaged Navier ndash;Stokes (RANS), compared with highly
accurate Large Eddy Simulations (LES). The simulations were performed at
the challenging running conditions of engine relevant Mach (0.67) and
Reynolds (300,000) numbers. The work looks at the effects of off-design
incidence and the influence of different free-stream disturbances on loss
prediction. From the highly accurate data sets produced by the LES the work
is able to show how loss attribution varies under different conditions, and
goes on to compare how well RANS captures these changes. It was found that
overall loss trends are captured well by RANS but substantial differences
exist when comparing individual loss sources, which are shown to vary
significantly under different running conditions. The investigation into
loss attribution is performed using the Denton (1993) loss breakdown as well
as a novel application of the Miller (2013) mechanical work potential. In
addition to the discovery of the variation in the sources of loss, the
comparison between the loss analyses highlighted some of the limitations of
the Denton loss breakdown, which was shown to have increasing error under
large off-design incidence or in the presence of discrete disturbances.
From the comparison of the loss breakdown analyses and LES and RANS flow
field results, new insight into the characteristics, limitations and short
comings of current modeling techniques have been found. The variation in
the sources of loss under different running conditions was also
discovered.
Jake completed his undergraduate at the University of Manchester after which
he went on to do his masters at Imperial college London in computational
fluid dynamics. He then moved to the University of Southampton to complete
his PhD, focusing on loss predictions of axial compressor cascades using
CFD. He is now currently a research fellow at the University of Melbourne,
continuing his work on axial compressors, and focusing on numerical model
development and improved loss prediction techniques of turbo machinery
flows.
Completion: Compressible turbulent wakes in constant area pressure gradients: simulation and modelling
Chitrarth Lav
University of Melbourne
3.30pm Friday 23 August 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Improving turbomachinery efficiency today is directly related to quantifying
and reducing the various sources of losses. Of these, the wake mixing loss,
resulting from wakes produced by the blade trailing edge, is of prime
interest. These wakes, when developing spatially through the periodic
constant area passage in the stator-rotor row, are exposed to pressure
gradients which can impact the wake evolution and consequently the wake
mixing loss. Since a study on the effect of the pressure gradient in
isolation is not possible in an actual turbomachine stage, a canonical case
study, of a statistically two-dimensional turbulent wake, is proposed to
understand and predict the underlying flow physics arising from the presence
of pressure gradients. Through the use of compressible high-fidelity
simulations, the relevant flow quantities are scrutinised to explain the
effect of the pressure gradients. While the understanding developed through
the high-fidelity data is invaluable, prediction of these flows is still a
challenge with the existing URANS, due to the poor underlying turbulence
closure. Thus, in the next stage, the prediction of the wake flow using
URANS is improved by developing a new closure, obtained using the
high-fidelity data of the zero pressure gradient (ZPG) wake and a symbolic
machine-learning algorithm. The results from the implemented closure show
an error of less than 1% with the calculation being 400 times cheaper than
the DNS. The developed closure is also evaluated on 6 additional cases: ZPG
wakes at different Reynolds numbers and wakes in the presence of pressure
gradients, to test if the closure is re-usable and robust to changing flow
conditions, with promising results. Thus, the results from the study
undertaken, both from a simulative and modelling standpoint, can serve as a
guide in predicting and minimising the loss produced by wake mixing.
Chitrarth's supervisors are Richard Sandberg and Jimmy Philip.
Reducing aerofoil–turbulence interaction noise with bio-inspired designs
Lorna Ayton
University of Cambridge
3.30pm Friday 16 August 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
A dominant source of aeroengine noise arises when the unsteady wakes shed
from rotors interact with downstream stators. This so-called leading-edge
noise cannot be eliminated, but it can be reduced. By altering the spanwise
geometry of the leading edge of an airfoil it is known through experimental
testing that leading-edge noise can be significantly reduced over broadband
frequencies. In recent years, a multitude of different shapes have been
tested and all are seen to have benefits for different frequency ranges,
which may be ideal for the reduction of tonal noise, but the question
remains; which design is optimal for broadband noise reduction? A similar
unavoidable source of noise occurs when the turbulent boundary layer over
an aerofoil scatters off the sharp trailing edge, in so-called trailing-edge
noise. Similar variations to the spanwise geometry are effective in reducing
this noise, but also alterations to the porosity or flexibility of the
trailing edge have been seen to be efficient, however again no predictive
tool for the optimum adaptation has been developed. This talk will present a
range of theoretical models for different aerofoil adaptations which are
known to reduce broadband turbulence interaction noise, and will illustrate
how they may be used as a stepping stone towards determining optimally quiet
designs.
Lorna completed her PhD under the supervision of Nigel Peake in 2014 in the
Department of Applied Mathematics and Theoretical Physics at the University
of Cambridge. From there she undertook a 3-year Junior Research Fellowship
funded by Sidney Sussex College, and now is funded by a 5-year EPSRC Early
Career Fellowship held in DAMTP. Her research focusses on developing
theoretical models for aeroacoustics, in particular aerofoil-turbulence
interaction, and on advancing fundamental mathematical methods for
application to acoustic scattering problems.
Population balance equation for turbulent polydisperse flows
Fatemeh Salehi
Macquarie University
3.30pm Friday 9 August 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The transport of polydispersed droplets and solid particles in turbulent
flows is relevant to a wide range of applications such as particle
dispersion in the atmosphere, fire suppression systems and liquid spray fuel
injection in diesel engines and gas turbines. The dynamics of droplets and
particles transported by a turbulent flow involves a complex series of
inter-related phenomena including dispersion, surface growth or shrinkage,
breakage, agglomeration and nucleation. In this talk, Dr Salehi will present
an effective model based on the probability density function (PDF) form of
the population balance equation (PBE) for polysized and polyshaped droplets
and solid particles in turbulent flows. A key novelty of this method lies in
the inclusion of an explicit consideration of the inertial effects and the
shape of particles in the PDF-PBE formulation.
Dr Fatemeh Salehi is a Lecturer at the School of Engineering at Macquarie
University. She received her PhD from the School of Photovoltaic and
Renewable Energy Engineering in the University of New South Wales in 2015.
She then worked as a postdoctoral research associate at the University of
Sydney before she joined Macquarie University in 2018. Her expertise is in
the development of physical models for computational fluid dynamic
simulations of turbulent flows with emphasis on particle and droplet flows
which are common in a wide range of engineering applications from drug
inhalers to fuel injectors in diesel engines and gas turbines. Dr Salehi's
research also involves combustion modelling and hydrogen safety to advance
renewable reliable energy technologies. Dr Salehi is currently a chief
investigator in $329 million Blue Economy CRC and the co-leader of
Macquarie's contribution to Hydrogen Storage and Safety program of the
CRC.
Advanced acoustic microfluidic manipulation for active micro-control
David Collins
University of Melbourne
3.30pm Friday 28 June 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
How can we move something too small to touch? Very high frequency sound
fields (>100 MHz) provide a promising avenue for microscale manipulation,
yielding acoustic wavelengths on the order of individual cells. Such
micromanipulation has a wide range of biomedical applications. Using surface
acoustic waves (SAW), a dynamic actuation method uniquely suited to
generating microscale forces, I've performed deterministic sorting,
nanoparticle concentration, droplet generation and the first acoustic 2D
patterning of individual cells. In recent work, I'm creating microscale
acoustic waveguides for even more refined activities. Combined with other
approaches, acoustic forces show substantial promise for structuring
individual cells and human tissues at the microscale.
I recently joined the Department of Biomedical Engineering at the
University of Melbourne, having come here from a joint Postdoctoral Research
Fellow at the Massachusetts Institute of Technology (MIT) and the Singapore
University of Technology and Design (SUTD). I have 26 publications on novel
acoustic actuation methods and the physics of advanced microscale
manipulation, including work appearing in Physical Review Letters, Nature
Communications and Science Advances, and have given multiple invited talks
on my work. Interests include novel acoustofluidic waveguides and arbitrary
acoustic field generation for non-uniform micropatterning in tissue
engineering applications. I completed my undergraduate degree at in
Biomedical Engineering from the University of Melbourne, and was awarded
the Bill Melbourne Medal for best engineering PhD thesis at Monash
University.
Transition to turbulence in the ocean boundary layer beneath ice shelves
Catherine Vreugdenhill
DAMTP, University of Cambridge
3.30pm Friday 21 June 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The melting of ice shelves around Antarctica has implications for ocean
circulation and sea-level rise. However, the picture of ocean-driven melting
is incomplete. Here, we use large-eddy numerical simulations to resolve all
but the smallest scales of turbulence in an idealised ocean domain of a
current underneath an ice shelf. The domain is bounded from above by the
ice shelf base under melting conditions that lead to a vertical
stratification in both temperature and salinity. The mixing of warm, salty
water towards the ice base drives melting, but the resulting meltwater
freshens the water column and stabilizes the stratification, suppressing
turbulence and mixing. The transition from stratified to fully turbulent
flow is examined and found to strongly influence the melt rate. Conditions
are chosen similar to those at Antarctic sites to compare with observations
and allow exploration of future scenarios.
Cat is a Postdoctoral Research Associate with the Atmosphere–Oceans
Group at the University of Cambridge. Her research centres on small-scale
processes in the ocean that can have important impacts on ocean dynamics and
climate. In 2017, Cat completed a PhD in Geophysical Fluid Dynamics at the
Australian National University where she used numerical simulations,
laboratory experiments and theory to examine transport by deep convection in
the ocean. Cat's postdoc research investigates the ocean-driven melting of
ice shelves in collaboration with researchers at the British Antarctic
Survey. By improving our knowledge of these small-scale processes she hopes
to help improve their representation in larger scale ocean and climate
models.
Microfluidics for biomedical applications
Reza Nosrati
Monash University
3.30pm Friday 14 June 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Microfluidic methods offer several advantages over their traditional
macro-scale counterparts by extending the possibility of biomedical research
based on the idea of miniaturization. These miniaturized platforms provide
opportunities to manipulate cells and biological processes at the
single-cell level and develop nature-inspired technologies for diagnostic
and therapeutic applications. For example, in the context of fertility,
microfluidics can match the geometry of micro-confined regions within the
female reproductive tract, thus, presenting opportunities for
biomimicry-based selection of sperm that reflect the in vivo process. In
this talk, I will provide an overview of our work in developing
microfluidic technologies for (a) sperm analysis and selection, and
(b) understanding bacterial motility. These microfluidic platforms present
several promising avenues to address our large-scale health and
environmental challenges.
Dr. Reza Nosrati is a Lecturer in the Department of Mechanical &
Aerospace Engineering at Monash University. Prior to joining Monash
University, he was an NSERC postdoctoral fellow in the Department of
Chemical Engineering at Queen's University (2016–2018). Dr. Nosrati
received his Ph.D. in Mechanical Engineering from the University of
Toronto (2016), his M.Sc. in Mechanical Engineering from the University of
Tehran (2010) and his B.Sc. in Mechanical Engineering from Amirkabir
University of Technology (2007).
Dr. Nosrati's research focuses on small-scale fluid mechanics
(microfluidics and nanofluidics), with applications in cell biology,
chemistry and medicine. He is a pioneer in microfluidics for male fertility
and assisted reproduction. He has authored papers in top-tier scientific
journals like Nature Communications, Nature Reviews Urology and Clinical
Chemistry. Dr. Nosrati has received numerous prestigious awards and
recognitions, including the 2016 Colton Medal for research excellence in
Microsystems and Nanotechnology, and the 2018 ROYAN International Research
Award for outstanding contributions to Embryology and Andrology.
Effect of deformations on the flow over a ringwing
Christian Thomas
Monash University
3.30pm Friday 31 May 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Deformations on a wing surface can bring about significant changes in flight
performance characteristics. The ability to accurately predict
laminar–turbulent transition processes is fundamental to improving the
design of future aircraft. Several numerical methods are introduced and
applied to a model airfoil with small indentations that are sufficient to
establish separated flow and enhance boundary layer instability.
Dr. Christian Thomas received his PhD in 2007 from Cardiff University in
fluid dynamics. Following his PhD, Christian undertook postdoctoral
positions at the University of Western Australia and Imperial College
London. Christian spent 2013 working with Airbus Group Innovations and has
been a Lecturer at Monash University since June 2017.
Microfluidics of left-right symmetry breaking in mammal embryos
Andrey Kuznetsov
North Carolina State University
3.30pm Friday 24 May 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
We developed an approximate method for modelling the flow of embryonic fluid
in a ventral node. We simplified the problem as flow in a 2D cavity; the
effect of rotating cilia was modeled by specifying a constant vorticity at
the edge of the ciliated layer. We also developed an approximate solution
for morphogen transport in the nodal pit. The solutions were obtained
utilizing the proper generalized decomposition (PGD) method. We compared our
approximate solutions with the results of numerical simulation of flow
caused by the rotation of 81 cilia, and obtained reasonable agreement in
most of the flow domain. We discuss locations where agreement is less
accurate. The obtained semi-analytical solutions simplify the analysis of
flow and morphogen distribution in a nodal pit.
Dr. Kuznetsov joined Department of Mechanical and Aerospace Engineering at
NC State University in 1998 after his postdoctoral appointments at
Ruhr-University of Bochum (Germany), Ohio State University, and Vienna
University of Technology. He received PhD in Mechanical Engineering from
Russian Academy of Sciences in 1992. Dr. Kuznetsov's research interests are
in the general area of numerical modeling, including fluid mechanics,
transport in porous media, transport in living tissues, bioheat transport,
bioconvective sedimentation, Newtonian and non-Newtonian flows, flows in
microgravity, and turbulence. His most recent research addresses axonal
transport, left-right symmetry breaking in mammal embryos, modeling of
electroporation, and thermal dose optimization in cancer treatment using
hyperthermia. He attracted funding from many national and international
agencies, including DARPA, NSF, NASA, EPA, NATO, USDA, DTRA, NTC, and
Eastman Chemical. He is also an affiliate faculty member of the UNC/NCSU
Biomedical Engineering Department, Fellow of American Society of Mechanical
Engineering, Associate Editor of the ASME Journal of Heat Transfer and the
Journal of Porous Media, and a winner of a prestigious Humboldt Research
Award. In 2014, Dr. Kuznetsov was elected as a Member of the Scientific
Council of the International Center of Heat and Mass Transfer
(ICHMT).
Air quality, winds, and atmospheric physics in the western U.S.
Heather A. Holmes
Atmospheric Turbulence and Air Quality Laboratory |
Website
University of Nevada, Reno
3pm Thursday 23 May 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Left: wildfire smoke plume near Reno, NV; right: temperature inversion
in the Salt Lake Valley.
Nearly 70 million people live in the western U.S. and growth continues as
this region experiences rapid population increase. According to the 2010
U.S. Census regional population growth, from 2000–2010, in the
western U.S. was 13.8%, the second largest growth region in the nation.
While the population density in this region is low and correspondingly there
should be fewer sources of anthropogenic air pollution, many areas in the
western U.S. are currently designated as maintenance areas or are in
non-attainment for at least one of the criteria air pollutants as defined
by the National Ambient Air Quality Standards (NAAQS). This is exacerbated
by unique air pollution sources (e.g. wind blown dust and wildfire smoke)
and the local meteorological and orographical affects in the Intermountain
Region. The mountainous terrain and elevation changes create synoptic
weather patterns that lead to complex winds and atmospheric mixing that
impact air pollution transport, dispersion, and accumulation.
This talk will focus on two distinct conditions with complex atmospheric
physics that impact air quality throughout the western U.S. The first, is
when local stagnation events, initiated by slow moving high pressure
systems, cause pollutants to become trapped in cold dense air on valley
floors, often referred to as temperature inversions. Research advancements
in quantifying the turbulent fluxes and surface energy balance closure
during temperature inversions will be shown using observations from the
wintertime Persistent Cold-Air Pool Study (PCAPS) in the Salt Lake Valley,
Utah. The second, is wildfire events that are common in the western U.S.
when complex flows lead to terrain induced wildfires from dry, downslope
winds, especially during drought conditions. Recent advancements in
satellite remote sensing algorithms to quantify aerosols will be discussed
and results of ongoing air quality modeling efforts to estimate wildfire
smoke exposures in the western U.S. will be presented.
Heather Holmes is an Assistant Professor in the Department of Physics and
Atmospheric Sciences Program at the University of Nevada, Reno. She
received her PhD in Mechanical Engineering from the University of Utah in
2010, where she focused on experimental investigations to study air
pollution, turbulence, meteorology, and chemistry in the atmospheric
boundary layer. She has three years of postdoctoral training, including two
years at Georgia Tech where her focus was to analyze air pollution data to
better understand how emission sources impact air quality and to develop
exposure metrics for health effects studies. Her current research group uses
ground-based monitors, atmospheric models, and satellite remote sensing to
investigate atmospheric physics, air pollution sources, transport and
dispersion, and provide data for human health and public policy
assessments.
Nonlinear exact coherent structures in pipe flow and their instabilities
Ozge Ozcakir
Monash University
3.30pm Friday 17 May 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Research on coherent structures in cylindrical pipes is an area of much
recent activity. Of particular interest are traveling wave (TW) states at
large Reynolds number R. The existence and stability of these states, and
their connection in phase space play important roles in understanding both
transition and large R behavior of pipe flows. In this talk, we consider
possible asymptotic structures at large Reynolds number R and identify
numerically calculated solutions as finite R realisation of a nonlinear
viscous core (NVC) state that collapse towards the pipe center with
increasing R at a rate R−1/4. We also identify previous
numerically calculated states as finite R realisation of a vortex wave
interacting (VWI) state with asymptotic structure similar to the ones in
channel flows studied earlier by Hall & Sherwin (J. Fluid Mech.,
vol. 661, 2010, pp. 178–205). In addition, stability features of both
VWI and NVC states are investigated. Numerical calculations confirm
lower-branch travelling waves have slow and low dimensional unstable
manifolds suggesting their relevance to transition in turbulence.
Ozge Ozcakir obtained her PhD in Mathematics from the Ohio State University.
After completion of her degree, she worked as a full-time lecturer briefly
at OSU. She joined School of Mathematics at Monash University in 2015 as a
Research Fellow under supervision of Prof. Philip Hall. She has recently
been appointed as a Lecturer at Monash University. Her primary research
interest is numerical investigation of nonlinear coherent structures to
understand the mechanism that leads to turbulence in different geometries.
Using numerical and asymptotic techniques, she has studied coherent
structures at large Reynolds numbers. Her current work focuses on
investigating the effects of changes in viscosity parameter and the effect
of periodic suction/blowing at the pipe wall on coherent structures
numerical simulations.
An update on K41 versus K62
Robert A. Antonia
University of Newcastle
3.30pm Friday 3 May 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Although Kolmogorov's (1962) correction (K62) to his 1941 theory (K41) has
been embraced by many turbulence researchers, our recent work suggests that
there are no valid reasons for abandoning K41. In particular, analytical
considerations, based on the NS equations, which take into account the
finite Reynolds number effect, together with the available experimental and
numerical data, seem to confirm a tendency towards the simple and elegant
predictions of K41 as the Reynolds number increases. This is especially true
when the focus is on scales which lie within the dissipative range. Since
K62 is predicated on the idea that the effect of large scales on small
scales continues to increase as the Reynolds number increases, it cannot be
reconciled with the 4/5 law, a result that is exact only when the Reynolds
number approaches infinity and the effect of the large scales is
negligible.
Robert Antonia studied Mechanical Engineering at the University of Sydney,
and received his PhD in 1970. Following a post-doctoral year at Imperial
College on a CSIRO fellowship, he joined the University of Sydney as a
lecturer in Mechanical Engineering in 1972. He was appointed to the Chair of
Mechanical Engineering at the University of Newcastle in 1976. Over the
period 2001–2005, he was ARC Professorial Fellow at the University of
Newcastle. In 2004, he was awarded a Citation Laureate for Engineering by
Thomson ISI and was elected to the Australian Academy of Science. Since
2005, he has been an Emeritus Professor at the University of
Newcastle.
Molecular fluid dynamics
Edward Smith
Brunel University
3.30pm Friday 5 April 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Left: turbulent minimal channel flow simulated using molecular dynamics
(MD) and compared to CFD. Top right: posts on a wall at the molecular scale
and Bottom right: two phase flow with the moving contact line and
liquid-vapour interface
Short of quantum mechanics, molecular dynamics (MD) is the most accurate
model of fluid motion we have. By simulating the motion of individual
molecules, we get a complete picture down to the nanoscale, capturing the
complete energy cascade, visco-elastic behaviour, slip boundaries,
liquid-vapour interfaces and phase change.
Far from the kinetic picture of occasional molecular collisions, complex
fluid behaviour emerges from the evolving structure of a particle lattice.
From the solution of Newton's law between particles, emerges the entire
spectrum of fluid phenomena. In this talk I will introduce the MD
methodology, highlighting the link between traditional continuum fluid
dynamics and demonstrating similarities with Couette flow. I will outline
the unique insights provided, including the microscopic origins of stress
and viscosity, what happens near boundaries, the liquid-vapour interfaces,
molecular heat flux and bubble nucleation. Finally, I will talk about the
simulation of the Couette minimal channel flow (Re=400) using molecular
dynamics, and discuss the insight this can provide into our understanding of
fundamental fluid phenomena and turbulence.
Edward Smith
(
www.edwardsmith.co.uk) works on
multi-scale simulation which aims to combine particle and continuum methods.
He earned his PhD at Imperial College London developing theoretical and
computational techniques for the coupled simulation of molecular dynamics
(MD) and computational fluid dynamics (CFD). He was awarded the
post-doctoral excellence fellowship and simulated the first example of
near-wall turbulence using MD. He spent some time working in Swinburne
Australia, before moving to Chemical Engineering at Imperial to work on
multi-phase flow and the moving contact line. His next move was to Civil
Engineering at Imperial to develop software (www.cpl-library.org) and
techniques to link particles and continuum for granular flows, before taking
up a permanent position at Brunel University London.
An alternate length scale for Reynolds number and Rossby number in the context of insect-like wings decouples the aspect-ratio effects
Shantanu Bhat
Monash University
3.30pm Friday 29 March 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
A stable leading-edge vortex formed over a rotating or flapping insect-like
wing is known to be a primary reason behind an extra lift acting on the
wing. Inspired from earlier studies at high Reynolds-number on the high
aspect-ratio aircraft wings, the wing chord has been used as the reference
length-scale, even for the insect-scaled wings. However, the flow structure
on a typical low aspect-ratio insect wing is highly three-dimensional. As
per the conventional scaling, this flow structure has been observed to be
influenced by aspect ratio, Reynolds number, and Rossby number. Our work
shows that the flow structure scales better with the wingspan, which we
propose as the new reference scale in the context of insect wings. Use of
this modified scaling for the Reynolds number and Rossby number decouples
the effects of the aspect ratio. Interestingly, this also helps reconcile
the apparently conflicting trends in the previous aspect-ratio studies on
insect wings.
Shantanu Bhat is working as a research officer in Fluids Laboratory for
Aeronautical and Industrial Research (FLAIR) at the Department of
Mechanical and Aerospace Engineering, Monash University. He received his PhD
from Monash University in August 2018. He has been working on the
aerodynamics of the flapping wings of insects and rotating winged seeds. In
the past, he has worked on the stall flutter of small turbomachine blades at
the Indian Institute of Science, where he obtained his masters by research.
He has also served as a lead engineer for GE Aviation in India, where he
worked on the aero-design of GE's LEAP engine combustor. His research
interests broadly involve vortex dynamics, biolocomotion, and bluff body
flows.
What is data assimilation and how can we use it to improve models of physical systems?
Craig Bishop
School of Earth Sciences and ARC Centre of Excellence for Climate Extremes, University of Melbourne
3.30pm Friday 22 March 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
On the one hand, you have an imperfect computer model of some idealized or
filtered version of a physical system such as the atmosphere; on the other
hand, you have been taking imperfect observations of corresponding parts of
this system. How can you combine these two entities to obtain state
estimates to initialize computer model forecasts and/or expose computer
model error? These are the central questions addressed by data assimilation.
In this talk, I'll give a brief introduction to data assimilation and
highlight how my research has been approaching some of the major challenges
currently facing the weather and climate prediction communities.
Prof Bishop completed his PhD at Monash University and performed
his postdoctoral research at the University of Reading where he was awarded
the Royal Meteorological Society's L. F. Richardson prize. He was then
Professor at Pennsylvania State University before turning to operational
weather prediction at the Naval Research Laboratory in Monterey, California.
He returned to Melbourne in June 2018. His current research mainly focusses
on the data assimilation science of using models, observations and advanced
estimation theory to initialize ensemble forecasts and to identify and
account for systematic and stochastic aspects of model error in ensemble
forecasting. Prof Bishop's ensemble-based data assimilation and
ensemble-forecasting techniques are now used by leading environmental
forecasting agencies such as the European Center for Medium Range Weather
Forecasting, the UK Met Office, the German weather service, the Swiss
weather service, the US National Weather Service, the US Navy and the
Japanese, Korean and Brazilian Meteorological agencies.
Tornado-like vortices in coriolis–centrifugal convection
Susanne Horn
UCLA
3.30pm Friday 15 March 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Rotating thermal convection is one of the most important mechanisms for
generating turbulence in geophysical settings, such as planetary interiors,
atmospheres, and oceans. Rotating Rayleigh–Bénard convection,
in which a fluid heated from below, cooled from above and rotated about its
vertical axis, is the canonical model used in laboratory experiments and
numerical simulations that captures the essential flow physics. However, in
most theoretical and numerical studies, rotation has only been considered in
terms of the Coriolis force, whereas the centrifugal force has been
neglected. Hence, it remains largely unknown how flows are altered by
centrifugal buoyancy, in particular, in the turbulent regime. We have
recently begun to address this deficit by numerically characterising
rotating convection including the full inertial term, i.e., by including
both Coriolis and centrifugal forces. This work has revealed that in
Coriolis–centrifugal convection storm-like structures can develop,
ranging from eyes and secondary eyewalls found in hurricanes and typhoons,
to concentrated helical upflows characteristic of tornadoes. Here, I will
mainly focus on the tornado-like vortices. These vortices are not only
self-consistently generated, but also exhibit the physical and visual
features of type I tornadoes, i.e. tornadoes that form within mesocyclones
contained in supercell thunderstorms. I will show that centrifugal buoyancy
is, in fact, highly relevant for the understanding of these geophysical
vortices, and likely a key component in next-generation models of tornado
physics.
Susanne Horn is a DFG (German Research Foundation) Research Fellow at the
Department of Earth, Planetary, and Space Sciences at the University of
California, Los Angeles where she investigates fluid problems that are
relevant in a geophysical context, including tornado dynamics and planetary
core liquid metal convection. Prior to this, she was a Postdoc at the
Department of Mathematics at Imperial College London, working on data-driven
decomposition methods with application to aeroacoustic noise. She has
received her PhD in physics from the University of
Göttingen.
Some recent developments in the low-order modelling and estimation of fluid flows
Ati Sharma
University of Southampton
3.30pm Friday 8 March 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Modelling and estimating fluid flows is a difficult problem. Fluid flows
are well described by the Navier–Stokes equations, but these are
nonlinear PDEs, which are difficult to solve in a general way. Much recent
work has focused on finding low-dimensional approximations to fluid flow
systems, either by abstracting them from data generated from experiment and
simulation or by finding suitable approximations to the equations. This talk
will discuss recent approaches; Dynamic Mode Decomposition (DMD), Koopman
mode analysis and resolvent analysis. The approaches will be explained, and
recent applications to flow analysis and estimation will be presented.
Ati Sharma is Associate Professor at the University of Southampton. Ati's
undergraduate degree is in Physics (University College London) and PhD and
postdoc in Control Engineering (Imperial College). Over the last fifteen
years, Ati has turned to modelling, estimation and control fluid flows and
has published extensively in this area. His most cited paper is from 2010
introducing resolvent analysis for turbulent flows. Somewhere in there he
was also an options trader for JP Morgan.
Advanced low noise aircraft configurations and their assessment–past, present and future
Zoltán Spakovszky
MIT Gas Turbine Laboratory
3pm Monday 4 March 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Aircraft noise remains the key inhibitor of the growth of air transportation
but the focus of the noise mitigation strategies has changed. As the
propulsor fan pressure ratio (FPR) is decreased and bypass ratio (BPR) is
increased for improved fuel burn and reduced environmental impact, the
propulsion system noise is reduced near or even below the noise level of the
airframe. Jet noise has become less of a concern and, during approach and
landing, the acoustic signature is predominantly set by the airframe. Novel
aircraft concepts and architectures, enabled by distributed, more
integrated, and boundary layer ingesting propulsion systems, pose new
aero-acoustic problems which require innovative approaches and call for
teaming and collaboration as the technological challenges cut across
disciplines. One past example of such a collaborative research effort was
the Silent Aircraft Initiative (SAI), aimed at the conceptual design of an
aircraft imperceptible to the human ear outside the airport perimeter. The
initiative brought together researchers from academia, industry and
government agencies. This talk gives a brief summary of the Silent Aircraft
Initiative, the SAX-40 aircraft design, and the noise reduction technologies
which were pursued. A decade past SAI, novel aircraft architectures such as
the D8 double bubble aircraft, the outcome of a joint effort between MIT,
Aurora Flight Sciences and Pratt & Whitney, are being pursued in the
quest of reducing the climate impact of aviation. With regulations
continuing to reduce the allowable aviation noise emission levels, both new
challenges and new opportunities are emerging. Electric, hybrid, and
turbo-electric aircraft concepts are currently being investigated as
potential game-changers. Independent of the level of electrification, noise
will remain a major issue as air transportation is growing and mobility
might become a key driver. The talk will discuss a selection of enabling
technologies and their implications on acoustics and noise and will give a
perspective on future trends and new directions in aero-acoustics required
to address the challenges.
Dr. Spakovszky is Professor of Aeronautics and Astronautics at the
Massachusetts Institute of Technology and the director of the Gas Turbine
Laboratory. He obtained his Dipl. Ing. degree in Mechanical Engineering from
the Swiss Federal Institute of Technology (ETH) Zürich and his MS and
Ph.D. degrees in Aeronautics and Astronautics from MIT. Dr. Spakovszky's
principal fields of interest include internal flows in turbomachinery,
compressor aerodynamics and stability, dynamic system modeling of aircraft
gas turbine engines, micro-scale gas bearing dynamics, and aero-acoustics.
He currently directs analytical and experimental research in these areas and
teaches graduate and undergraduate courses in thermodynamics, propulsion and
fluid mechanics, and aero-acoustics. He has authored a large number of
technical papers in refereed journals and has been awarded several ASME
International Gas Turbine Institute best paper awards, the ASME Melville
Medal, the ASME Gas Turbine Award, the ASME John P. Davis Award, a NASA
Honor Award, several Aero-Astro Undergraduate Advising/Teaching Awards,
and the Ruth and Joel Spira Award for Excellence in Teaching. Dr. Spakovszky
is a technical consultant to industry and government agencies, a Fellow of
the ASME, an Associate Fellow of the AIAA, and served as the chair of the
turbomachinery committee and review chair of the ASME International Gas
Turbine Institute, and as an associate editor for the ASME Journal of
Turbomachinery.
Dense and dilute particulate flows: sediment erosion and transport phenomena
Aman Kidanemariam
University of Melbourne
3.30pm Friday 22 February 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
In this talk I will present my previous work on the problems of sediment
transport and subaqueous pattern formation by means of high-fidelity direct
numerical simulations. The peculiarity of the simulations lies on the fact
that all relevant scales of the turbulent flow are taken into account, even
the near-field around each individual sediment grain. The numerical method
employed features an immersed boundary technique for the treatment of the
moving fluid–solid interfaces and a soft-sphere model to realistically
treat the inter-particle contacts. Our study has provided, first and
foremost, a unique set of spatially and temporally resolved information on
the flow field and the motion of individual particles which make up the
sediment bed. Furthermore, based on the rigorous analysis of the generated
data, the fluid flow and particle motion over the evolving sediment bed are
studied in great detail, providing novel insight into the different
mechanisms involved in the processes of sediment pattern formation.
Dr. Kidanemariam is a DFG (German Research Foundation) Research Fellow who
recently joined the Fluid Mechanics Research Group here at Melbourne. He
earned his PhD degree in 2015, in Civil Engineering, Geo and Environmental
sciences at Karlsruhe Institute of Technology (KIT), Germany. His research
background and interests lie in the field of computational fluid dynamics
and high-performance computing applied to environmental flow problems. His
previous research has particularly emphasized on dilute and dense
particulate flows, turbulence-particle interaction, and shear flow driven
sediment erosion and transport phenomena. He is a recipient of the
prestigious Ercoftac Da Vinci Award 2015 for outstanding quality of PhD
research as well as several other scholarships and awards. Part of his work
has been featured in 'Focus on Fluids' article in Journal of Fluid
Mechanics, highlighting its novelty and impact in the field of sediment
transport modeling.
Statistical state dynamics: a new framework for understanding turbulent flows
Navid Constantinou
Australian National University
3.30pm Friday 8 February 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Statistical state dynamics (SSD) provides a new perspective for studying
mechanisms in turbulence. SSD is the study of the dynamics that governs the
flow statistics themselves. In flows with anisotropy and structured
coherent mean flows a closure at second order of the SSD turns out to be
both extremely useful and insightful. SSD reveals some key relevant physical
processes that are often obscure in the single-realization flow dynamics.
Many such phenomena are intrinsically associated with the dynamics of the
statistical state and have an analytic expression only in SSD. Examples
consist of instabilities that arise intrinsically from interaction between
the coherent and the incoherent components of the turbulence. Here, I will
use a second-order closure of the SSD to study the self-organization of
turbulent flows and the formation of large-scale structure both in planetary
turbulence and in wall-bounded flows. I review some of the recent advances
including: jet formation in planetary turbulence as an instability of the
turbulent state, noise-induced roll–streak formation in
pretransitional Couette flow, and elucidating the role of the
very-large-scale motions (VLSMs) in the regeneration mechanism in shear
flows away from the wall.
Navid grew up in Cyprus. He is a physicist at heart and he's fascinated with
geophysical fluid dynamics. His Ph.D. research focussed on atmospheric
dynamics and in particular the study of how the sub polar jet stream
interacts with atmospheric turbulence. After his PhD, he was awarded a NOAA
Climate & Global Change postdoctoral fellowship (2015–2017) at
Scripps Institution of Oceanography, University of California San Diego.
There, he tried to shed insight on some of the physical processes that occur
in the ocean by studying the interaction among oceanic eddies, large-scale
ocean currents, and underwater mountains at the ocean floor. Since May 2018,
he joined the ARC Centre of Excellence for Climate Extremes as part of the
climate variability project focussing on the circulation of the Southern
Ocean. More at
www.navidconstantinou.com.
On the origin of wall turbulence: where is the wall?
Ricardo García-Mayoral
University of Cambridge
3.30pm Friday 25 January 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Surfaces that exhibit small textured features can interact with
near-wall turbulence and increase or reduce drag, which is of great
interest to the aerospace, naval, transport and energy industries. This
talk will discuss some of the dynamic mechanisms at play in that
interaction, with particular emphasis on flows over transitional
roughness and over superhydrophobic and anisotropically permeable
substrates. In flows over smooth surfaces, an origin for the wall-normal
coordinate can be defined unambiguously at the surface itself, where all
three velocity components vanish. Over complex surfaces, in contrast,
different components of the flow can experience different virtual
origins, where they perceive the apparent presence of a smooth wall. In
the limit of vanishingly small texture, in what constitutes the
'viscous' or 'linear' regime, the main effect of the surface is an
offset between the origins perceived by the mean flow and by the
background turbulence, which remains otherwise smooth-like. For larger
texture sizes, richer dynamic mechanisms produce a deviation from this
viscous regime. These mechanisms vary from texture to texture, but we
will discuss two frequent ones. The first is the direct influence of the
texture granularity, which induces a texture-coherent flow, and which we
will discuss in the framework of rough and superhydrophobic surfaces.
The second is the appearance of spanwise-coherent structures, arising
from a Kelvin–Helmholtz-like instability connected with surface
transpiration, which we will discuss in the framework of permeable
substrates.
Dr. García-Mayoral is a lecturer in the Department of Engineering
at the University of Cambridge. He obtained his PhD from Universidad
Politécnica de Madrid, and in 2011, conducted postdoctoral research
at the Center for Turbulence Research (CTR) at Stanford University before
joining Cambridge. His research interest is in wall-bounded turbulence
with a particular emphasis on complex surfaces.
Properties of the mean momentum balance in polymer drag-reduced channel flow
Chris White
University of New Hampshire
3.30pm Friday 18 January 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
In the first part of the talk, Dr. White will briefly outline his ongoing
research projects. In particular, recent work on the development of a simple
dynamical model of the turbulent boundary layer will be presented. The
formulation of the model is based on recent findings that reveal that at
large Reynolds numbers the inertially dominated region of the turbulent
boundary layer is composed of large-scale zones of nearly uniform momentum
segregated by narrow fissures of concentrated vorticity. It will be shown
that a simple model that exploits these essential elements of the turbulent
boundary layer structure can reproduce statistical profiles of the
streamwise velocity that agree remarkably well with those acquired from
direct numerical simulation at high Reynolds number.
The main part of the talk will discuss research related to the phenomenon of
polymer drag reduction in wall-bounded turbulent flows. Here a mean momentum
equation based analysis of polymer drag reduced channel flow is performed to
evaluate the redistribution of mean momentum and the mechanisms underlying
the redistribution processes. Similar to channel flow of Newtonian fluids,
polymer drag reduced channel flow is shown to exhibit a four layer structure
in the mean balance of forces that also connects, via the mean momentum
equation, to an underlying scaling layer hierarchy. The self-similar
properties of the flow related to the layer hierarchy appear to persist, but
in an altered form (different from the Newtonian fluid flow), and dependent
on the level of drag reduction. With increasing drag reduction, polymer
stress usurps the role of the inertial mechanism, and because of this the
wall-normal position where inertially dominated mean dynamics occurs moves
outward, and viscous effects become increasingly important farther from the
wall. For the high drag reduction flows of the present study, viscous
effects become non-negligible across the entire hierarchy and an inertially
dominated logarithmic scaling region ceases to exist. It follows that the
state of maximum drag reduction is attained only after the inertial sublayer
is eradicated. According to the present mean equation theory, this coincides
with the loss of a region of logarithmic dependence in the mean
profile.
Dr. White received his Ph.D. in Mechanical Engineering from Yale University
in 2001. From 2001–2004 he was Postdoctoral Research Fellow at
Stanford University. Following his post-doctoral work, he joined Sandia
National Laboratories as a Senior Member of the Technical Staff in the
Combustion Research Facility. In 2006, he joined the Mechanical Engineering
Faculty at the University of New Hampshire. Dr. White's research expertise
is in the thermal-fluid sciences with a focus on the turbulent transport of
mass, momentum, and energy. His research to date is of both fundamental and
applied nature in the areas of polymer drag reduction, turbulent boundary
layers, piston engines, flow induced erosion, biomass, and thermal
management. Dr. White received an NSF CAREER award in 2009. In 2016,
Dr. White's and co-author Godfrey Mungal's 2008 Annual Review of Fluid
Mechanics paper "Mechanics and prediction of turbulent drag reduction with
polymer additives" was designated as a Highly Cited Paper (top 1% in the
field of Physics) by the Thompson Reuters Essential Science Indicators.
Dr. White currently has funding from NSF, ONR, NAVAIR, and NAVSEA.
A tale of two quasi-linear dynamical systems: modulated waves and shear-driven instabilities
Greg Chini
University of New Hampshire
3.30pm Friday 11 January 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The quasi-linear (QL) approximation has facilitated the prediction and
understanding of a broad variety of fluid dynamical phenomena, ranging from
the quasi-biennial oscillation of the zonal winds in the equatorial
stratosphere to the emergence of exact coherent states (ECS) in wall-bounded
turbulent shear flows. The QL reduction involves a decomposition into mean
and fluctuation components and retention of fluctuation/fluctuation
nonlinearities only where they feed back on the mean dynamics. Although
sometimes invoked as an ad hoc simplification, the QL approximation
can be justified asymptotically for certain flows exhibiting temporal scale
separation, as will be demonstrated here through two complementary examples.
In the first example, a new type of acoustically driven mean flow is
identified and analyzed. Specifically, it is shown that when a
high-frequency acoustic wave of small amplitude ε interacts with a
stratified fluid, an unusually strong form of acoustic streaming can occur,
with the time-mean flow arising at O(ε) rather than the more
commonly realized O(ε2) value. The resulting two-way
coupling between the wave and streaming flow is self-consistently captured
in a QL dynamical system. In the second illustration, a QL model of strongly
stratified turbulent shear flows is derived. Spectrally non-local energy
transfers, associated with small-scale non-hydrostatic instabilities induced
by the relative horizontal motion of large-scale hydrostatic eddies, are
economically represented. The model is used to compute ECS in strongly
stratified Kolmogorov flow and to evaluate the mixing efficiency achieved by
these nonlinear states. For both the wave- and shear-driven systems, new
asymptotic analyses are developed that enable integration of the dynamics
strictly on the slow time scale associated with the mean flow, yielding
significant computational efficiencies while simultaneously promoting
physical insight.
Greg Chini is Professor of Mechanical Engineering and Co-Director of the
Integrated Applied Mathematics Ph.D. Program at the University of New
Hampshire. He earned his doctorate in Aerospace Engineering at Cornell
University, with a focus on a fluid mechanics and applied mathematics, and
has held visiting positions at Nottingham University, Caltech, the
Institute for Pure and Applied Mathematics (IPAM) at UCLA, and the Kavli
Institute for Theoretical Physics (KITP) at UCSB. In 2016, he was elected
to the faculty of the Woods Hole Summer Program in Geophysical Fluid
Dynamics. Prof Chini's research centers on the application of nonlinear
mathematics and high-fidelity numerical simulations to important
environmental, energy, and resource challenges facing society. Specific
research themes include self-organization and extreme transport in fluid
turbulence, multiscale phenomena in geophysical fluid dynamics and
geophysics, and mathematical modeling of energy and resource systems.
Some implications of self-similarity in canonical wall turbulence
Beverley McKeon
Caltech
3.30pm Monday 17 December 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
There has been much recent progress with regards to characterizing
self-similar behavior in wall turbulence in experiments, in simulation, and
in the mean and instantaneous forms of the Navier–Stokes equations.
We identify commonalities and differences between these observations, and
draw some conclusions concerning the requirements for self-similarity and
self-sustaining processes in wall turbulence. Recent developments with
respect to resolvent analysis are exploited to identify low-rank
representations of these processes, their signatures and their limitations
in physical and spectral space. We close with a discussion of some
outstanding challenges related to the existence, self-sustenance and
modeling of self-similar solutions and structures in the canonical
flows.
The support of the U.S. Air Force Office of Scientific Research under grant
FA 9550-16-1-0361 and the U.S. Office of Naval Research under grant
N00014-17-1-2307 is gratefully acknowledged.
Beverley McKeon is Theodore von Karman Professor of Aeronautics at the
Graduate Aerospace Laboratories at Caltech (GALCIT). Her research interests
include interdisciplinary approaches to manipulation of boundary layer flows
using morphing surfaces, fundamental investigations of wall turbulence at
high Reynolds number, the development of resolvent analysis for modeling
turbulent flows, and assimilation of experimental data for efficient
low-order flow modeling. She was the recipient of a Vannevar Bush Faculty
Fellowship from the DoD in 2017, the Presidential Early Career Award
(PECASE) in 2009 and an NSF CAREER Award in 2008, and is an APS Fellow and
AIAA Associate Fellow. She is the past editor-in-chief of Experimental
Thermal and Fluid Science and currently serves as an associate editor of
Physical Review Fluids, and on the editorial boards of the AIAA J., Annual
Review of Fluid Mechanics and Experiments in Fluids. She is the APS
representative and Vice Chair Elect of the US National Committee on
Theoretical and Applied Mechanics.
Harnessing the energy of wave driven turbulence at a fluid surface
Nicolas Francois
Australian National University
3.30pm Friday 7 December 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
When a laminar flow becomes turbulent, its energy is spread over a range of
scales in a process named energy cascade. It has recently been discovered
that turbulent flows can be forced by steep Faraday waves at a fluid
surface. Those flows possess features of two-dimensional turbulence. In
particular, an inverse energy cascade has been identified and a substantial
amount of energy is stored into the turbulent fluctuations. An interesting
question is whether it is possible to efficiently use the energy of this
strongly out-of-equilibrium state.
In the wave driven turbulence, we show how to create floating devices able
to extract energy from the turbulent motion fluctuations by coupling with
underlying features of the energy cascade. The operational principle of
these devices relies on the rectification of the chaotic motion of
correlated bundles of fluid trajectories. By changing the shape of the
device, we can turn it into a vehicle or a rotor powered by
turbulence.
Nicolas Francois was awarded his PhD in physics of fluids and polymers from
the Université de Bordeaux. Since 2012, Nicolas has worked as an
experimentalist in the Physics of Fluids Laboratory at the Australian
National University. Nicolas studies Lagrangian aspects of Turbulence and
surface hydrodynamics notably in the recently discovered Faraday wave
driven turbulence. He is also interested in the physics of complex fluids
and granular matter.
Multi-scale interactions between the lower atmosphere and the urban canopy
Karin Blackman
CNRS
12.30pm Tuesday 20 November 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The urban boundary layer consists of complex coherent structures, such as
large-scale low momentum regions and intermittent turbulent sweeps and
ejections, which are responsible for the transport of heat, momentum and
pollution. Although these structures have been well identified
qualitatively, their quantitative relationship is still unknown. Wind tunnel
modelling of flow over simplified rough terrain consisting of either
three-dimensional or two-dimensional roughness elements are able to
reproduce these structures and are used to investigate the nonlinear
relationship between large-scale momentum regions and small-scales induced
by the presence of the roughness. As the temporally resolved small-scale
signal is not available Linear Stochastic Estimation is used to decompose
the flow into large and small-scales and confirm that the large-scale
structures within the overlying boundary layer influence the small-scales
close to the roughness through a nonlinear mechanism similar to amplitude
modulation. Changing terrain configuration from 3D to 2D roughness results
in a modification of the nonlinear relationship closer to the shear layer
that develops near the top of the obstacles. Triple decomposition of the
kinetic energy budget confirms that the nonlinear relationship that exists
between large-scale momentum regions and small-scales close to the roughness
is related to energy transfer between these structures. Application of an
existing predictive model shows that the canopy flow regimes influences both
the superposition and amplitude modulation close to the roughness. Finally,
a combination of roughness geometries and Reynolds numbers are used to
validate the predictive model in the urban boundary layer.
Dr Blackman obtained her PhD from Ecole Centrale de Nantes and is now
a researcher in atmospheric mechanics and turbulence at CNRS.
Vortex formation on surging airfoils and high advance ratio rotors
Anya Jones
University of Maryland
3.30pm Thursday 8 November 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Experiments were performed on wing surging in a water tank, a swept wing
pitching in a wind tunnel, and a Mach-scaled slowed rotor at high advance
ratios. Time-resolved particle image velocimetry was used to characterize
the flow field around a blade element in the reverse flow region of the
rotor, and near the center of the wing in the non-rotating experiments. On
the rotor, four dominant flow structures were observed: the reverse flow
starting vortex, the blunt trailing edge wake sheet, the reverse flow
dynamic stall vortex, and the tip vortex. As advance ratio increases, the
duration of reduced time that the blade element spends in the reverse flow
region also increases. This affects the strength, trajectory, and predicted
vortex-induced pitching moment of the reverse flow dynamic stall vortex. The
results of this characterization and sensitivity study are compared to the
more canonical models of flow reversal and separation. The three-dimensional
rotor flows are found to have many similarities to canonical
two-dimensional models.
Anya R. Jones is an Associate Professor in the Department of Aerospace
Engineering at the University of Maryland, College Park. She received her
PhD in Aerodynamics from the University of Cambridge, United Kingdom, her
S.M. in Aeronautics and Astronautics from MIT, and her B.S. in Aeronautical
and Mechanical Engineering from Rensselaer Polytechnic Institute. Her
research is focused on the experimental fluid dynamics of unsteady and
separated flows. Her current projects focus on the flow physics of
large-amplitude gust encounters, separated and reverse flow rotor
aerodynamics, and flight through airwakes and other unsteady environments.
Prof. Jones has been awarded the AFOSR Young Investigator Award, NSF CAREER
Award, and the Presidential Early Career Award for Scientists and Engineers
(PECASE). Recently, she was awarded a Fulbright Scholar Award to the
Technion in Haifa, Israel and an Alexander von Humboldt Research Fellowship
to TU Braunschweig in Germany. She is currently chair of a NATO Research
Technology Organization task group on gust response and unsteady
aerodynamics, an associate fellow of AIAA, and a member of the Alfred
Gessow Rotorcraft Center.
Spatially localized structures in driven dissipative systems: theory and applications
Edgar Knobloch
University of California Berkeley
3.30pm Friday 2 November 2018
KevinMechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Spatially localized structures arise frequently in driven
dissipative systems. In this talk I will describe a number of
examples from different physical systems, followed by a discussion
of the basic ideas behind the phenomenon of nonlinear
self-localization that is responsible for their existence. I will
illustrate these ideas using a simple phenomenological model and
explain why the qualitative predictions of this model help us
understand the properties of much more complicated systems
exhibiting spatial localization, and specifically those arising in
fluid mechanics.
Edgar Knobloch studied Mathematics at the University of Cambridge.
In 1974 he received a J.F. Kennedy Scholarship to study theoretical
astrophysics at Harvard University. After receiving his PhD in 1978
he was a Junior Fellow of the Harvard Society of Fellows and a
Research Fellow at St John's College, Cambridge. He has been a
Professor of Physics at the University of California, Berkeley, ever
since. His interests range from dynamical systems theory, chaotic
dynamics, pattern formation, all the way to materials science and
geophysical and astrophysical fluid dynamics. He is a Fellow of the
American Physical Society and the Society for Industrial and Applied
Mathematics. He holds honorary doctorates from Université
Paul Sabatier in Toulouse, France, and Universidad
Politécnica de Madrid, Spain.
Experimental measurement of three-dimensional density fields and the coupling of direct numerical simulations to experiments
Callum Atkinson
Monash University
3.30pm Friday 26 October 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
While the last 20 years have seen significant advances in our ability to
experimentally measure micro to metre scale instantaneous velocity fields
(including time-resolved volumetric measurements), the measurement of fluid
density and temperature fields is far less evolved. For many quantities in
compressible and heated flows, this requires us to rely on computationally
expensive simulations, generally at Reynolds numbers far below those we
desire. Even in incompressible flows, our best velocity measurements, while
able to readily capture large scale information, are able to match the
fidelity of direct numerical simulations. This presentation will focus on
recent developments towards providing volumetric instantaneous density
measurement in compressible flows, along with attempts to use large scale
experimental data as an input to drive the convergence of direct numerical
simulations, similar to how field observations are used to enhance weather
predictions.
Dr. Atkinson received his PhD in Mechanical Engineering in 2012 as a
Cotutelle PhD between Monash University and Ecole Centrale de Lille in
France on the development and application of three-dimensional measurement
techniques for investigating the 3D structure of wall-bounded turbulence.
This included the development of the MLOS approach that is now widely used
in commercial software for tomographic particle image velocimetry. His
post-doc work focused on the experimental establishment of a
self-similar adverse pressure gradient turbulent boundary layer and
complementary direct numerical simulations. He was awarded an ARC Discovery
Early Career Researcher Award (DECRA) fellowship in 2016 and is currently
developing experimental techniques and facilities for the simultaneous
measurement of fluid temperature and velocity fluctuations in heated
boundary layers over natural and engineered surface roughness, while looking
at means to directly couple the relative strengths of the optical
measurements with higher fidelity direct numerical simulations.
Multi-phase fluid behaviour and thermal characteristics in flow through curved ducts
Tilak Chandratilleke
Curtin University
3.30pm Friday 19 October 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Fluid flow behaviour in curved passages is fundamentally different to that
in straight channels due to the secondary flow induced by centrifugal
effects from passage curvature. Such flows have characteristic vortex
structures producing spiralling fluid motion through curved passages, hence
promoting fluid mixing even under laminar flow conditions and enhancing wall
heat transfer process. Secondary flow also leads to hydrodynamic instability
under certain flow conditions, introducing additional vortices to the flow
for more pronounced fluid mixing. The secondary flow structures in
multi-phase fluids are much more complex than in single phase fluid since
the individual fluid phases are affected differently by the centrifugal
forces. This presentation outlines the current research knowledge in this
field, focussing on specific contributions made by the author towards the
scientific understanding of the single and two-phase flow through curved
ducts and their thermal characteristics.
Professor Tilak Chandratilleke is the Head of Mechanical Engineering
Discipline at Curtin University, Perth, Western Australia. He obtained his
PhD in two-phase flow and boiling heat transfer from the Cambridge
University in the United Kingdom, supported by Trinity College, Cambridge
and the UK Atomic Energy Authority. He has worked as a consulting engineer
in the UK and the USA for several years prior to joining the academia. His
experimental and numerical research spans from the discovery of microlayer
theory for bubble growth in boiling to pulsed-jet electronic cooling,
microfluidics, thermal radiation, and single and two-phase heat transfer in
curved flow passages (topic of the presentation). He has contributed to
thermal industry applications with unique and patented concepts, including
the radiation shield for preventing excessive heating of water pipe network
in Western Australia and the development of Thermoelectric-based
fridge/freezer. He serves as an editor for the Institution of Mechanical
Engineers (UK) Journals, as national chair of the Australasian Thermal
Engineering Society (AFTES), and an executive member of the Engineers
Australia WA Mechanical Panel. He was a member of the ARC College of Experts
until early this year.
Subcritical transition in wall-bounded shear flows
Jacob Cohen
Technion
3.30pm Friday 12 October 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The current study focuses on a sub-critical transition scenario of
wall-bounded flows which are stable with respect to infinitesimal small
disturbances (Couette flow and Plane Poiseuille flow for subcritical
Reynolds numbers). Accordingly, a linear transient growth mechanism is
initiated by four decaying normal modes, the initial structure of which
corresponds to counter-rotating vortex pairs. It is shown that the four
modes are enough to capture the transient growth mechanism. More
importantly, it is demonstrated that the kinetic energy growth of the
initial disturbance is not the key parameter in this transition mechanism.
Rather, it is the ability of the transient growth process to generate an
inflection point in the wall-normal or spanwise directions and consequently
to make the flow susceptible to a three-dimensional disturbance leading to
transition to turbulence. The model utilizes separation of scales between
the slowly evolving base-flow and the rapidly evolving secondary
disturbance. Because of the minimal number of modes participating in the
transition process, it is possible to follow most of the key stages
analytically, using the multiple time scales method. It is only due to
nonlinear effects that the base flow becomes unstable with respect to an
infinitesimal disturbance. The theoretical predictions are compared with
direct numerical simulations and very good agreement with respect to the
growth of the disturbance energy and associated vortical structures is
observed, up to the final stage just before the breakdown to turbulence.
Finally, the mechanism governing these transition stages (in the odd
transition scenario) is very similar to the one described by the vortex
dynamics model, previously proposed by the authors to explain the
experimentally observed generation of a train of hairpins.
Jacob Cohen is a Professor and Sydney Goldstein Chair in Aeronautical
Engineering at the Faculty of Aerospace Engineering, Technion – Israel
Institute of Technology. He is the former Dean of the faculty (2015-2018)
and currently serves as the head of the Technion Wind Tunnel Complex. Jacob
received his Bachelor (1980) and Master (1982) degrees in Mechanical
Engineering at the University of Tel-Aviv, Israel, and PhD (1986) at the
AME department in University of Arizona. He then completed two and a half
years as a Postdoc fellow at MIT before returning to the Israel (Technion).
His main research interests are in experimental, theoretical and numerical
study of laminar-turbulent transition, study of the evolution and control of
coherent structures in wall bounded and free shear flows, hydrodynamic and
thermal instabilities and unsteady phenomena.
Reconstruction and estimation of flows using resolvent analysis and data-assimilation
Sean Symon
University of Melbourne
3.30pm Friday 5 October 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
A flow reconstruction methodology is presented for incompressible,
statistically stationary flows using resolvent analysis and
data-assimilation. The only inputs necessary for the procedure are a rough
approximation of the mean profile and a single time-resolved measurement.
The objective is to estimate both the mean and fluctuating states of
experimental flows with limited measurements which do not include pressure.
The input data may be incomplete, in the sense that measurements near a body
are difficult to obtain with techniques such as particle image velocimetry
(PIV), or contaminated by noise. The tools developed in this talk are
capable of filling in missing data and reducing the amount of measurement
noise by leveraging the governing equations. The reconstructed flow is
capable of estimating fluctuations where time-resolved data are not
available and solving the flow on larger domains where the mean profile is
not known.
The first part of the talk is centered on developing the tools necessary for
this procedure. The second part of the talk discusses the reconstruction of
flow around a NACA 0018 airfoil at zero angle of attack and a chord-based
Reynolds number of 10250. The mean profile, obtained from PIV, is
data-assimilated and used as an input to resolvent analysis to educe
coherent structures in the flow. The resolvent operator for non-amplified
temporal frequencies is forced by an approximated nonlinear forcing. The
amplitude and phase of the modes are obtained from the discrete
Fourier-transform of a time-resolved probe point measurement. The final
reconstruction contains less measurement noise compared to the PIV
snapshots and obeys the incompressible Navier–Stokes equations.
Sean Symon completed his undergraduate degree in Aerospace Engineering at
the University of Maryland. He then completed his masters in Aeronautics at
the California Institute of Technology and participated in the masters
exchange program between GALCIT and Ecole Polytechnique. In France, he
received a masters in fluid mechanics and worked with David
Quéré studying drop dynamics on macro-textured
superhydrophobic surfaces. Upon returning to Caltech, Sean joined Beverley
McKeon's group working on data-assimilation and resolvent analysis. He is
now working as a post-doc with Simon Illingworth and Ivan Marusic studying
the attached eddy model in the context of the linearized
Navier–Stokes equations.
Enhancing heat transfer by inducing resonance in natural convection boundary layers
Chengwang Lei
University of Sydney
3.30pm Thursday 27 September 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
In natural convection systems, the rate of heat transfer depends on the
state of the thermal boundary layers forming on heat transfer surfaces,
which may be laminar, transitional or turbulent. The heat transfer rate is
much higher in the turbulent state than that in the laminar state. The
transition of the thermal boundary layers from laminar to turbulent state
may be advanced by either active or passive techniques. In this
presentation, I will introduce a unique strategy to enhance heat transfer by
triggering resonance in thermal boundary layers. Resonance occurs when a
system is excited at frequencies close to its natural frequency. As a
result, strong oscillations of the system are induced. Resonance may take
place in a thermal boundary layer if it is perturbed at its characteristic
(natural) frequency. I will describe the process for determining the
characteristic frequency of thermal boundary layers and the application of
resonance for enhancing heat transfer. Both active and passive strategies
for triggering resonance and enhancing heat transfer will be
demonstrated.
Chengwang Lei is currently a professor and Deputy Head of School of Civil
Engineering at The University of Sydney, Australia. He is also the Deputy
Director of the Centre for Wind, Waves and Water. Chengwang received his
Bachelor (1988) and Master (1992) degrees in Mechanical Engineering at
Huazhong University of Science & Technology in China and PhD (2000) in
Civil and Resource Engineering at The University of Western Australia. His
main research interest is in fundamental fluid mechanics related to buoyancy
driven flows with environmental, industrial and domestic applications. His
research involves experimental modelling, numerical simulation and
analytical investigation of diverse thermal flow problems. In recent years
Chengwang has been conducting concentrated research on solar thermal based
passive strategies for building ventilation and thermal comfort. He has
published widely in the international literature and at leading national and
international conferences. More information about Prof Chengwang Lei may be
found on his profile page
here.
On the scaling of the statistics of adverse-pressure-gradient turbulent boundary layers
Atsushi Sekimoto
Osaka University
12.30pm Tuesday 25 September 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
A characteristic boundary layer thickness is introduced to scale turbulence
statistics in zero-/adverse-pressure gradient turbulent boundary layers
(ZPG-/APG-TBLs). The characteristic length scale, which is termed the
`shear thickness', corresponds to the location which corresponds to the end
of an actively sheared region in a turbulent shear flow, where the
nondimensional Corrsin shear parameter is approximately constant. Using the
friction and pressure velocity, the Reynolds stresses in TBLs over a wide
range of APGs collapse with those in a ZPG-TBL. The present scaling is used
to analyse the mean velocity and the kinetic energy balance in TBLs, and
compare them to other shear flows. Furthermore, a scaling for small-scale
properties will also be presented. The present scaling for TBLs over a wide
range of pressure gradients is considered to be key to the development and
application of turbulent models.
In 2011, the speaker completed his Ph.D. in thermo-fluid mechanics group at
Osaka University, and he joined the Fluid Mechanics group in the Technical
University of Madrid (UPM) as a post-doctoral fellow. In 2016, he worked as
a research fellow in the Laboratory for Turbulence Research in Aerospace
& Combustion (LTRAC) at Monash University. He is now Assistant Professor
in the Dept. of Chemical Engineering in the School of Engineering Science at
Osaka University. His main research interests are on the turbulence
structures and the control of the temporal-space dynamics.
Accurate and efficient methods for reduced-complexity modelling in fluid mechanics
Scott Dawson
Caltech
3.30pm Friday 21 September 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
This talk will explore several recent developments that improve upon the
efficiency, accuracy, and theoretical understanding of methods for modal
decomposition and reduced-order modelling in fluid mechanics. First, I will
propose a method for the analytic approximation of the shape of resolvent
modes in shear-driven turbulence, based on approximations to pseudospectral
modes of scalar operators. This approach provides a theoretical framework
for understanding the origin of observed structures, and gives a method for
mode estimation without the need for large numerical computations. Next, I
will focus on the dynamic mode decomposition (DMD), which provides a means
of extracting dynamical information from fluids datasets. I will show that
DMD is biased to sensor noise, and will subsequently present a number of
modifications to the DMD algorithm that eliminate this bias, even when the
noise characteristics are unknown. Lastly, I will discuss a number of
approaches by which linear data-driven modelling techniques may be utilised
and extended for accurate modelling of nonlinear systems.
Scott Dawson is currently a postdoctoral scholar within the Graduate
Aerospace Laboratories at the California Institute of Technology. Prior to
this, he completed his Ph.D. in Mechanical and Aerospace Engineering at
Princeton University, and honours degrees in Mechanical Engineering and
Mathematics at Monash University. In January, he will commence a position as
an assistant professor at the Illinois Institute of Technology. His research
interests include modelling, optimisation and control in fluid mechanics,
with a particular focus on turbulent shear flows and unsteady aerodynamic
systems.
Incomplete mixing in porous media
Daniel Lester
RMIT University
3.30pm Friday 14 September 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Experimental image of evolving dye plumes resulting from Stokes flow over
packed glass spheres.
Mixing, transport, reaction and dispersion of fluids and solutes in
heterogeneous porous media is a fundamental problem of widespread importance
in nature and engineered systems, ranging from geophysical and biological
systems to microfluidics and chemical processing. Despite over a century of
research, quantification of fluid mixing in heterogeneous porous media is
largely based on a macro-dispersion (well-mixed) paradigm that does not
resolve incomplete mixing at either the pore- or Darcy-scales. In recent
years, significant advances have been made to better understand, predict and
control mixing, transport and dispersion across scales using a combination
of Lagrangian methods (dynamical systems theory, Hamiltonian chaos) and
stochastic modeling (continuous time random walks, Markov models) to develop
ab initio models of such phenomena. In this talk I shall present a brief
overview of these advances and models for fluid mixing at the pore- and
Darcy-scales, and discuss future research directions at the interface of
porous and open flows.
Daniel completed his PhD in Chemical Engineering at University of Melbourne
in 2003 on the deformation, flow and separation of concentrated colloidal
suspensions prior to undertaking a Postdoc in the Advanced Thermofluids Lab
at CSIRO on the topic of Lagrangian chaos and mixing in 2005. He joined the
(then) Mathematics, Statistics and Informatics division of CSIRO as a
Research Scientist in 2007 prior to joining RMIT University as a Senior
Lecturer in 2014, where his current research interests involve the rheology
and flow of complex fluids, fluid chaos and mixing, and transport and
reactions in porous media.
Broadband noise predictions of an axial compressor operating at low Reynolds number
Oscar Wilsby
University of Melbourne
3.30pm Friday 7 September 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Government regulations on noise are moving the importance of acoustic
requirements to earlier stages of consumer product design. For
turbomachinery applications such as axial fans and compressors, it is
crucial for the design engineer to be able to accurately capture noise
trends and understand the minimum noise level of a particular design. To be
able to make noise predictions in an industrial setting, low order CFD must
be used to produce accurate statistics of turbulence. However the modeling
assumptions inherent in these methods make this a challenging task. This
talk investigates the use of wall-resolved LES to study noise sources of an
axial compressor operating at low Reynolds number and highlights the
deficiency of current RANS based CFD for acoustic predictions.
Oscar Wilsby completed his undergraduate, masters and PhD at the University
of Cambridge, working on aeroacoustic predictions for industry under
sponsorship of Dyson Technologies Ltd. He recently started working in
Professor Richard Sandberg's group on developing new data driven models for
airfoil noise prediction.
The role of convection on the basal melting of Antarctic ice shelves
Mainak Mondal
Australian National University
3.30pm Friday 31 August September 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Schematic of a sloping Antarctic ice shelf along with a enlarged snapshot of
the boundary layer flow field (inset). The along-slope velocity
(ζη-plane) and cross-slope convective velocity (yη-plane) and
spatial distribution of meltrate (ζy-plane) at the ice interface is
shown here at ambient temperature, T
b = 1° C and ambient
current, U
b = 0.05 m/s.
Melting of Antarctic ice shelves has a large impact on ocean circulation,
future sea level rise and the global climate. Most of the ice shelves in
Antarctica are sloped forward into the ocean, forming an ice cavity
underneath. The turbulent transport of heat and salt into the ice interface
melts the ice and drives convective wall plumes that play a crucial role in
the basal melting. Ice bathymetry and various ambient flows like tides,
waves and sub-mesoscale eddies further modify the plumes. The regional and
global ocean models work at scales over 100 meters and rely on crude
sub-grid scale parameterization of convection and turbulent processes at the
ice-ocean boundary layer, causing uncertainties in the estimation of the
melt rate.
I have examined the role of micro scale turbulent processes at the ice ocean
boundary using Direct Numerical Simulation (fully resolving convection and
turbulence, see figure). I carry out simulations by varying the slope of the
ice shelves, changing the strength of ambient flow and including sub-glacial
discharge. The results show that the melt rate is controlled by the slope of
the ice face with decreasing melt rate at shallower slopes. Over the
geophysical flow regime, convection is the key parameter that controls the
heat and salt transfer into the ice face and hence the melt rate. The
results from this study significantly widen our present understanding of
basal melting and can improve the ice-ocean parameterizations for
large-scale models.
Mainak did his bachelors with major in physics and later a postgraduate
diploma in astrophysics from BIFR India. His earlier research interest was
on stellar dynamics. As a summer intern, he did an observational project on
'Morphological Evolution of Planetary Nebulae' from Indian Institute of
Astrophysics. He later moved into geophysical fluid dynamics and did a
master in atmospheric science from IIT Kharagpur. His master thesis was on
'Effects of aerosol on BOB tropical cyclone Phailin'. He became
interested in boundary layer turbulence and found the very interesting
project at ANU on 'Turbulent melting of the Antarctic ice shelves'. Over his
PhD he explored the turbulence properties under the ice ocean boundary and
how melting occurs right at the ice ocean boundary.
Bluff body wake control
Jonathan Morrison
Imperial College
3.30pm Friday 24 August 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The coherent structures of a turbulent wake generated behind a bluff
axisymmetric body are investigated experimentally at a diameter based
Reynolds number ~ 2 × 105. Spectral and proper
orthogonal decomposition of base pressure measurements indicates that the
most energetic coherent structures retain the structure of the
symmetry-breaking laminar instabilities appearing as unsteady vortex
shedding with azimuthal wavenumber, m = ±1. In a rotating reference
frame, the shedding preserves the reflectional symmetry and is linked with a
reflectionally symmetric mean pressure distribution on the base. Due to a
slow rotation of symmetry plane of the turbulent wake around the axis of the
body, statistical axisymmetry is recovered in the long time average.
We investigate the effects of pulsed jet blowing on the turbulent wake. The
jet is formed from an annular orifice situated immediately below the
trailing edge and oriented in the direction of the freestream. By varying
the frequency and amplitude of the perturbation, we achieve a mean pressure
increase on the base of the body of up to 33%. Modal decomposition of the
base-pressure fluctuations reveals a nonlinear coupling between the
symmetric (m = 0) perturbation and higher order azimuthal modes
(m = ±1, ±2) that results in an asymmetric mean pressure
distribution. The pressure recovery is shown to be a broadband suppression
of energy across all modes with no preferential selection.
Lastly, we apply the modelling approach for the axisymmetric body described
above to the bistable mode of a rectilinear bluff body wake. We demonstrate
the validity of the model and its Reynolds number independence through
time-resolved base pressure measurements of the natural wake. Further,
oscillating flaps are used to investigate the dynamics and timescales of
the instability associated with the "flipping" process, demonstrating that
they are largely independent of Reynolds number. The modelling approach is
then used to design a feedback controller that uses the actuators to
suppress the bistable mode. The controller is successful, leading to
concomitant reductions in both lateral and stream-wise forces. Most
importantly the controller is found to be efficient, the actuator requiring
only 24% of the aerodynamic power saving.
Jonathan Morrison holds the chair of Experimental Fluid Mechanics in the
Department of Aeronautics at Imperial College. Recent work has focused on
fundamentals of turbulent flow and control including novel approaches to
flow control. He is currently exploring instabilities in transitional flows
as part of the LFC-UK Programme Grant and the correspondence between the
scalar and momentum fields as part of the Transpiration Cooling Systems
Programme Grant. Other recent work has developed novel drag-reduction
techniques for bluff-body flows both in open loop and with feedback
control. He is also exploring travelling surface waves for turbulent drag
reduction with support from Airbus. He is currently a member of the
"Aircraft of the Future" Advisory Group of the ATI. He is Director of, and
chairs the Management Board of the National Wind Tunnel Facility (NWTF),
funded by EPSRC and the ATI. He led an exhibit at the Royal Society Summer
Exhibition, 2014, "Smart Wing Design: Science Imitating Nature".
High-fidelity computational fluid dynamics (CFD) in industry: A retrospective and next steps
Vittorio Michelassi
Baker Hughes
3.30pm Friday 17 August 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The experience with non-reactive high-fidelity computational fluid dynamics
(CFD) for aero-thermal applications in General Electric spans across
low-pressure turbines, high-pressure turbines, radial and axial compressors
and turbine center-frames. Direct numerical simulation (DNS) and large-eddy
simulation (LES) were used for the investigation of design parameters impact
on performance across a wide design space leading the way for additional
testing and design changes that unlock further performance improvement. The
scale-resolved simulations data-set was also used for detailed
post-processing that shed light on some of the fundamental physical
processes that ultimately drive aerodynamic and thermal efficiency. The
large CFD data base was also used to improve unsteady Reynolds-averaged
Navier–Stokes (URANS) calculations, that is and will be the
workhorse in daily design iterations. This talk will first summarize the
results and impact obtained so far, and indicate the possible next steps
necessary for the full exploitation of scale-resolving CFD in
industry.
Prof Dr Vittorio Michelassi is Chief Consulting Engineer for Aerodynamics
at Baker Hughes, a GE Company, and GE Aviation. In his role he overlooks the
aero-thermal design of gas turbine components as well as the improvement of
design tools for all energy conversion related activities. Prior to joining
GE Aviation he worked in General Electric Global Research as aero-thermal
technologies Chief Engineer and from 2003 till 2011, he was principal
engineer and Manager Aero Design of General Electric Oil and Gas.
Before 2003 he was Professor of Gas Dynamics and Turbomachinery Aerodynamics
at the Universities of Firenze and Roma Tre, Italy. He received a Master in
Engineering from University of Florence, Italy, and a Master in Fluid
Dynamics from the Von Karman Institute for Fluid Dynamics, Rhode Saint
Genese, Belgium. He received his PhD from the University of Florence after
having conducted research at NASA Lewis Research Centre and Karlsruhe
Institute of Technology. He was visiting scientist at NASA Lewis, at the
Center for Turbulence Research in Stanford, at Karlsruhe Institute of
Technology. He participated several EU-granted research consortiums with
focus on turbomachinery and combustions where he gained a wide experience in
internal aerodynamics, with focus on turbine unsteady aerodynamics. He
worked in turbulence modelling applied to steady and unsteady
Reynolds-averaged Navier–Stokes simulations, as well as large-eddy
and direct numerical simulations, where he pioneered the industrial
application of high-fidelity CFD as a design investigation tool in
cooperation with academia. He is a member of ASME Turbomachinery Committee
and serves as a reviewer for international journals. He authored and
co-authored several journal and conference papers in the area of
turbomachinery design.
Optimal growth and two-dimensionalisation in liquid-metal duct flows under a uniform transverse magnetic field
Greg Sheard
Monash University
3.30pm Friday 10 August 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
A transient growth analysis of linearised three-dimensional disturbances is
conducted on a liquid metal flow in a duct with square cross section under a
uniform vertical magnetic field. This analysis reproduces published energy
amplifications at low Hartmann number, and for the first time reveals a
two-dimensionalisation of optimal disturbance structures in the magnetic
field direction at higher Hartmann number. Thereafter the predicted energy
amplifications are in excellent agreement with a quasi-two-dimensional model
for MHD flow developed by Sommeria & Moreau (1982).
Greg Sheard obtained his PhD from Monash University in 2004. He subsequently
held an Australian Postdoctoral Fellowship, and since 2006 has been a
faculty member of the Department of Mechanical and Aerospace Engineering at
Monash University. His research is concerned with the application of
high-order numerical methods for computational fluid dynamics to the study
of fluid flows and their stability. This has seen him explore problems in
bluff-body wakes, rotating flows, natural convection, and
magnetohydrodynamics.
The character and mechanics of flow-induced noise production from a finite span airfoil
Danielle Moreau
University of New South Wales
3.30pm Friday 27 July 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Many real-world technologies employ an airfoil that is wall-mounted and finite in
length with boundary layer impingement at the airfoil-wall junction and flow over
the tip. Examples include submarine hydrofoils mounted to a hull, wind turbine
blades mounted to a hub or the stators in an aeroengine that are connected to an
outer wall. An important aspect of airfoil noise production that has received little
attention in the past is the influence of airfoil three-dimensionality, boundary
layer impingement and flow at the tip on noise generation, which is the focus of
this seminar. Recent results will be presented from a series of airfoil flow and
noise measurement campaigns conducted in anechoic wind tunnels at Virginia Tech
(USA), the Brandenburg University of Technology (Germany) and UNSW. A combination of
acoustic array measurements, flow visualizations, surface pressure and unsteady wake
data are used to gain insight into the turbulent noise sources and the role of
three-dimensional vortex flow near the airfoil tip and wall junction in noise
production.
Danielle Moreau obtained her PhD from the University of Adelaide in 2010. Following
PhD completion, she worked as a research associate at the University of Adelaide for
five years. During this time, Danielle investigated the mechanics of bio-inspired
quiet airfoils and submarine hydrofoil noise generation. In 2015, Danielle moved to
UNSW in the position of lecturer. Her research focuses on the understanding and
control of flow-induced noise with the aim of quietening modern technologies.
Buoyancy and convection drive the ocean circulation
Taimoor Sohail
Australian National University
3.30pm Friday 13 July 2018
Mechanical Enginneering Seminar Room Level 3 (Room 311, Bldg 170)
Convection is a small-scale flow feature which exists in most fluid flows.
In the global ocean, convection is present wherever a buoyancy gradient is
present. Given the ever-present nature of convection in the ocean, it is
unfortunate that large-scale ocean models cannot resolve this process. As a
result, there is a significant gap in the understanding of the impact of
convection on ocean circulation. Whilst research in the area is still scant,
it has become increasingly clear that convection may have profound impacts
on ocean circulation, particularly in the North Atlantic and Southern
Ocean.
To explore this, we employ a high-resolution Direct Numerical Simulation to
model the Southern Ocean, whilst explicitly resolving all scales of fluid
flow, from millimetre-scale turbulent convection to large-scale jets and
overturning circulation. The idealised channel model consists of a surface
temperature gradient and constant surface wind stress, mimicking the
climatological conditions in the Southern Ocean. We find that convection
significantly enhances mixing and plays a major role in modifying the fluxes
of potential and kinetic energy the system. The energy fluxes are tightly
controlled by the buoyancy forcing (and resulting convection), with little
sensitivity to changing surface wind stress. In addition, the overall
mass- and heat-transport appears to be largely buoyancy-dominated, with
wind stress having a minimal impact on the system.
This research indicates that when fully resolved, buoyancy-forcing and the
small-scale flows associated with it may have a major role in driving ocean
circulation compared to surface wind stress, overturning conventional wisdom
on the topic.
Taimoor Sohail is a PhD Candidate in the Climate and Fluid Physics group at
the Research School of Earth Sciences, Australian National University,
Canberra. Completing a Bachelor's degree in Mechanical Engineering from
Lafayette College, USA, in 2014, Taimoor moved on to climate change policy
research in Pakistan, working for a local think tank for two years. It was
there he was inspired to further explore climate science, and found it to be
a good fit for the engineering skills he had picked up over the years. He
began his PhD in 2016 under the supervision of Dr. Bishakhdatta Gayen and
Dr. Andy Hogg. Taimoor's main research focus is small-scale flow processes
in the ocean, including submesoscale fronts, internal waves and convection.
His eventual aim is to work towards tying large-scale ocean modelling work
to more recent small-scale computational research conducted with DNS and LES.
Does aeolian sedimentation contribute to coral cay accretion and island development in the Maldives?
Mike Hilton
University of Otago
3.30pm Friday 6 July 2018
Mechanical Enginneering Seminar Room Level 3 (Room 311, Bldg 170)
The atolls of the Maldives contain over 1200 reef islands; including atoll
lagoon islands and numerous sand cays on reef platforms. Sand cays are
comprised entirely of biogenic sediments, primarily coral sand. Cay
formation at nodal zones has been attributed to wave refraction and
diffraction around and over reef platforms. They are unstable deposits that
may meander within these zones. Unvegetated sand cays are low and commonly
over-washed by local waves during high astronomical tides. They may also be
inundated by swell waves generated in the southern Indian Ocean and tsunami.
These processes are known to deposit sediment on vegetated islands, but
over-wash is unlikely to contribute to cay accretion in the absence of
vegetation. There remains, therefore, the conundrum of how cays transition
to stable and forested islands? I hypothesize that aeolian sedimentation, in
conjunction with stranded organic debris and the growth of early
successional plant species, may contribute sufficient depth of sediment to
allow the development of non-saline groundwater and the colonisation of
islands by forest tree species.
Wind speed and direction was observed at 1Hz over and 8-day period in
February 2018 using Windsonic 2D anemometers mounted on a mast at 5.8m,
0.53m and 0.05m. Additional anemometers were positioned across the surface
of this terrace. Aeolian sedimentation was observed using Wenglor laser
particle counters over a period of 8 days, with swinging sand traps and
erosion/accretion stakes. Surface topography, nabkha and island morphology
was surveyed using a laser level to a datum established by RTK-GPS and local
mean sea level (derived from RBR deployments).
Incident wind direction was mainly from the north east during the period of
fieldwork, consistent with the Northeast Monsoon (October to April).
Incident wind speed was typically 4–6m/s at 5.8m, however,
periods of wind speed in excess of 12m/s were recorded on two
occasions. These events, which were characterised by periods of relatively
high onshore wind speed lasting several minutes, followed by a reverse in
wind direction, appear to be driven by low-level outbursts under
cumulonimbus clouds. Wind speed at ground level (0.05m) during these events
reached 8m/s. Saltation and ripple development occurred during
these events, albeit the rates of sand flux were not high (with Wenglor
counts up to 200/s). Our observations occurred during the relatively weak
Northeast Monsoon. We conclude that aeolian sedimentation probably occurs
frequently on Maaodagalla, particularly during the more energetic Southwest
Monsoon.
The development of nabkha appears to make a significant contribution to
island elevation. The elevation of Maaodagalla does not exceed 1.0m above
the level of spring high tides and 0.6m above observed maximum wave run-up.
Therefore, nabkha development has contributed most of the elevation (0.5m)
of the island above the level of wave run-up. Of course, aeolian
sedimentation may be occurring concomitant with overwash processes. The
analysis of sediment texture and the GPR data is ongoing to determine the
nature of the aeolian facies across the island and on Mahutigalla. A
freshwater lens was found under Maaodagalla in almost all of the excavated
pits, which indicates the cays do not need to accrete much to generate
conditions for freshwater accumulation and the establishment of forest tree
species.
Associate Professor Hilton is a coastal geomorphologist at the University of
Otago, with interests in dune geomorphology, the biogeomorphology of
foredunes, flow over dunes, beach-dune sedimentation, foredune response to
environmental stress, and the impact of invasive species on dune form and
function. He is the Secretary of the International Society for Aeolian
Research, and past executive member of the New Zealand Geographical Society,
New Zealand Coastal Society, IGBP-LOICZ and received the New Zealand Order
of Merit in 2018 for services to coastal science and conservation.
Completion: Computed coronary arterial flow dynamics: from stented to rough surfaces
Winson Chen
University of Melbourne
3.30pm Friday 22 June 2018
Mechanical Enginneering Seminar Room Level 3 (Room 311, Bldg 170)
Coronary stenting as a standard treatment for coronary arterial diseases has
achieved a high success rate in recent years. However, post-stenting
complications still affect a small but significant subset of patients.
Better understanding of the in-stent haemodynamic environment represents the
key to reveal the physics associated with these complications. Computational
fluid dynamic toolkits are employed to simulate pulsatile blood flow inside
stented curved arteries. Arterial curvature and stent malapposition
introduce pronounced adverse haemodynamic behaviours such as flow
recirculation. It consequentially enhances localised in-stent restenosis and
aggregation of activated platelets.
To understand the effect of stent-induced roughness on laminar pulsatile
blood flow, simplifications of stented artery geometries were made such that
key roughness parameters can be systematically investigated. The effect of
roughness parameters on laminar pulsatile pipe flow is quantified in a 2D
parametric space which could be relevant in the stent design to minimise
adverse haemodynamic behaviours.
Mass, energy and vorticity conservation for the rotating shallow water equations on a non-affine cubed sphere geometry using mixed mimetic spectral elements
Dave Lee
Monash University
3.30pm Friday 15 June 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The preservation of conservation laws and leading order balance relations
in the discrete form helps to mitigate against biases and improves the
representation of dynamical processes for geophysical flows over long time
integrations. In this talk we will discuss the use of the mixed mimetic
spectral element method to preserve mass, vorticity and energy conservation,
as well as geostrophic balance, for the rotating shallow water equations
with optimal error convergence on the cubed sphere. The method is based on
the recently developed spectral element edge functions, which exactly
satisfy the fundamental theorem of calculus with respect to the standard
nodal basis functions. Compatible high order finite element spaces are
constructed via tensor product combinations of nodal and edge functions.
These allow for the annihilation of the curl by the divergence and the
preservation of the divergence theorem in the strong form, and the
annihilation of the gradient by the curl and the preservation of the
circulation theorem in the weak form, via Galerkin projections onto the
appropriate function spaces.
These mimetic properties are preserved independent of geometry, and the use
of the generalised Piola transformation between canonical and physical
space allows for both the preservation of conservation laws and the spectral
convergence of errors on the non-affine geometry of the cubed sphere. These
properties are confirmed via results for standard test cases. Preliminary
results for 2D turbulence on the sphere and the dispersion relation for
high frequency waves will also be presented.
Dave completed his PhD in Applied Mathematics at Monash at 2014, where he
worked on the development of spectral element methods to model weakly
nonlinear internal ocean waves. He then undertook a post doctoral position
at Los Alamos National Laboratory, where he worked on the development of
hybrid semi-Lagrangian / discontinuous Galerkin methods for transport in
ocean models, and with the generous support of his supervisors initiated an
independent research project into the use of mixed mimetic spectral elements
for geophysical flows. Prior to his PhD he worked as a computational
scientist at VPAC. He is currently a research associate in the Department of
Mechanical and Aerospace Engineering at Monash.
The cascade of energy in an anisotropic homogeneous turbulence experiment
Douglas Carter
University of Minnesota
3.30pm Friday 8 June 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
One of the most challenging aspects of turbulence is the dynamics of the
energy cascade. This is due to its nonlinear nature, which is intimately
linked to the ultimate breakdown of large eddies into small eddies. The
early ideas of a physical cascade introduced by Richardson were expanded
upon in the classic work of Kolmogorov such that the breakdown of eddies was
thought to occur locally via adjacent scales. In more recent years evidence
has mounted which shows that transfers of energy are often non-local, occur
across disparate scales, and can even cascade in the inverse direction. Here
we present data from a 2D particle image velocimetry (PIV) experiment
performed in a jet-stirred zero-mean flow turbulence box in air. The
turbulence can be tuned to have a large scale anisotropy ratio u'/v' (where
u' is along the axial direction of the jets and v' along the radial
direction) between 1.4 and 1.7. In this range the Reynolds number based on
the Taylor microscale varies approximately between 300 and 500. Employing
the second-order structure function, we show that anisotropy persists into
(and through) the inertial scaling range. The third-order structure
function, in the context of the Karman–Howarth–Monin equation,
reveals that the cascade of energy is split such that energy moves from
small to large scales along the radial direction and from large to small
scales along the axial direction. We further find that the variation in
large-scale turbulent kinetic energy is linked to the presence (or absence)
of dissipative structures, which play a central role in the cascade. By
conditioning the third-order structure function on PIV samples with
"hyperactive" or "sleeping" levels of small-scale activity, we find the
cascade of energy has a unique footprint for these distinct states. These
results are a marked departure from the theory of Kolmogorov and imply that
the central quantities which govern the overall energy transfer are
non-local and reveal a complex structure in scale space.
Douglas Carter is a PhD candidate from the University of Minnesota and
graduate student researcher at Saint Anthony Falls Laboratory in
Minneapolis, Minnesota. Prior to graduate school he obtained a BS in
Mechanical Engineering from the University of New Hampshire in 2014. His
interests include fundamental turbulence, innovation in designing and
performing measurements, as well as environmental flows such as dust storms
(particle–turbulence interaction) and rain clouds
(droplet–turbulence interaction).
Electro-mechanical energy harvesting from flutter of cantilevers in axial- and cross-flows
Richard Howell
Curtin University |
Website
3.30pm Friday 1 June 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The presentation will consist of two talks given at
FSSIC 2017.
1. We model the fluid-structure interaction of non-linear flutter of a
cantilever mounted upon a non-linear spring at the clamp in a uniform axial
flow. This permits us to compare results with those from a hybrid non-linear
system (a linear system mounted on a non-linear spring) and so to assess the
change in fundamental physical phenomena owing to the introduction of full
non-linear structural- and fluid-mechanics. We use numerical simulation for
the non-linear system while our state-space solution of the corresponding
linear system is used to guide the choice of parameters in the
investigation. We show that above the flow speed of flutter-onset for small
disturbances, amplitude growth leads to non-linear saturation so that the
system settles into finite-amplitude oscillations. The frequencies of these
oscillations evidence the dual-frequency characteristics of mount
oscillation observed in physical experiments. When the natural frequency of
the mount is low, we show that for a range of increases above the linear
critical speed the linear hybrid and non-linear systems evidence the same
frequency phenomena. However, the linear hybrid system evidences larger
oscillation amplitudes than the non-linear system. Therefore, the
stabilising effect of the non-linear structural terms outweighs the
destabilising effect of the non-linear fluid terms.
2. A twin cantilever system is spring-mounted on a bearing and investigated
experimentally in a cross flow in a wind tunnel; two types of bearing are
used, cylindrical with one degree of freedom and spherical with three. By
comparing the two systems, it is found that the spherical bearing system is
slightly more unstable and operates at a higher oscillation frequency, hence
having more favourable conditions for energy harvesting. The physical
manifestation of the destabilising effect of the spherical bearing is seen
in the yawing
figure-of-eight forward and backward motion of the
cantilevers about the mount, which can be observed by looking directly down
on the set-up. For the range of spring stiffnesses used in this
investigation, the power producing capabilities of both systems continue to
increase as system natural frequency reaches higher values.
Fluid dynamic properties of irregular, multi-scale rough surfaces
Thomas Jelly
University of Melbourne
3.30pm Friday 25 May 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Surface roughness increases fluid dynamic drag and induces a rise in the
mean momentum deficit called the roughness function. This has implications
for engineering systems which involve surfaces that, hydrodynamically
speaking, are rough as opposed to smooth. Some examples include: the
aero-thermal characteristics of ablated turbine vanes; the frictional
resistance of bio-fouled marine vessels and the levels of wall shear stress
in industrial-grade steel pipes. As a result, the fluid dynamic properties
of practical roughness topographies are of significant interest.
The roughness function is itself a function of the roughness height and the
roughness topography. Engineering rough surfaces with an equal roughness
height but different topographies can give rise to roughness functions that
vary by a factor of four. While the relationship between drag and the
roughness height is well-understood, the relationship between roughness
topography and fluid dynamic properties remains less clear. Accurately
predicting the fluid dynamic properties of a given roughness topography is
therefore non-trivial.
In this work, surface simulation methods from tribology have been
implemented in order to generate "realistic" rough surfaces with specified
topographical parameters (e.g. skewness and correlation lengths). Direct
numerical simulations (DNS) of fully-developed turbulent channel flow over
the generated surfaces have been performed in order to obtain their fluid
dynamic properties with the aim of establishing relationships between
topographical parameters and quantities such as the roughness function,
"form-induced" dispersive stresses and turbulence-induced Reynolds
stresses.
Dr. Thomas Jelly received his PhD in Mechanical Engineering from Imperial
College London. He has held previous post-doctoral positions at the
University of Cambridge and at the University of Glasgow. As of March 2018,
Dr. Jelly joined Prof. Andrew Ooi's research group in order to investigate
the fluid dynamic properties of rough-wall pulsatile pipe flows.
Large-eddy simulation of environmental turbulence: Langmuir cells in the ocean and aeolian morphodynamics on Mars
William Anderson
Mechanical Engineering Department, The University of Texas at Dallas, USA
3.30pm Friday 18 May 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Results from large-eddy simulation of microscale turbulence in Earth's
ocean, and in the atmosphere of Mars, are presented. The ocean mixed layer
- the first ∼ 100 m of the ocean, and the zone most closely modulated
by atmospheric forcing - regulates sequestration of anthropogenic carbon and
heat from the atmosphere, accelerates the dispersion of surface-laden oil,
and mixes agricultural nitrogen released at coastal inlets. Large-eddy
simulation has been used to model Langmuir turbulence in coastal zones,
which is accomplished by integration of the grid-filtered Craik-Leibovich
equations. The forcing required to sustain the counter-rotating Langmuir
cells is prescribed via the curl of vorticity and Stokes drift - an
idealized velocity profile representing the aggregate motion due to waves.
In contrast to the open ocean, where the mechanism sustaining Langmuir cells
eventually vanishes, it is found that the presence of bottom-boundary layer
shear results in distinctly different turbulence morphology. The scale of
Langmuir cells does not remain constant, and instead cells associated with
downwelling occupy the entire column; it is shown that this ostensible
"cell thickening" is a product of mechanical shear imposed by the seafloor.
This result has implications for benthic zone sequestration of surface
quantities, and for sediment erosion and suspension in coastal zones.
Results from simulation of atmospheric flow over crater-like geometries
resembling those found on Mars are shown. Mars is a dry planet with a thin
atmosphere. Aeolian processes - wind-driven mobilization of sediment and
dust - are the dominant mode of landscape variability on Mars. Craters are
common topographic features on the surface of Mars, and many craters on Mars
contain a prominent central mound (NASA's Curiosity rover was landed in
Gale crater). Using density-normalized large-eddy simulations, we have
modeled turbulent flows over crater-like topographies that feature a
central mound. Resultant datasets suggest a deflationary mechanism wherein
vortices shed from the upwind crater rim are realigned to conform to the
crater profile via stretching and tilting. This was accomplished using
three-dimensional datasets (momentum and vorticity) retrieved from LES. As
a result, helical vortices occupy the inner region of the crater and,
therefore, are primarily responsible for aeolian morphodynamics in the
crater. These results suggest that secondary flows - originating from flow
separation at the crater - have played an important role in shaping
landscape features observed in craters (including the dune fields observed
on Mars, many of which are actively evolving).
Anderson received his PhD in Mechanical Engineering from The Johns Hopkins
University in July 2011. He began as a tenure-track faculty in the
Mechanical Engineering Department at Baylor University in Fall 2011, and
moved to the University of Texas at Dallas in Fall 2014. His research
interests focus on inertial-dominated turbulent flows in the environment.
His research is supported by the Army Research Office (ARO), the Air Force
Office of Scientific Research (AFOSR), the National Science Foundation
(NSF), and the Texas General Land Office (TGLO). He is a 2014 recipient of
the AFOSR Young Investigator Program award.
Applications of synchrotron light to multi-phase fluid mechanics
Daniel Duke
Monash University
3.30pm Friday 11 May 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Non-invasive fluid mechanics experiments are often limited to flows that are
optically accessible. This quickly becomes problematic when multiple phases
are present, such as in sprays, cavitating flows and particle-laden flows,
or under extreme temperatures and pressures. Refraction at gas/liquid
interfaces and multiple-scattering from large numbers of particles, droplets
or bubbles can make quantitative optical measurements challenging. X-rays
offer a number of advantages over optical diagnostics due to the unusual
ways they interact with matter. X-rays can penetrate opaque media, but also
refract very weakly, allowing us to see through dense droplet and bubble
clouds without refractive effects. Synchrotron radiation provides a
collimated source of x-rays with orders of magnitude more flux than benchtop
or CT scanner x-ray sources, and with tunable wavelength. Synchrotron beams
can approach micron spatial resolution and sub-microsecond time resolution.
This presentation will introduce a range of synchrotron diagnostics for
fluid mechanics and example use cases. These includes radiography,
phase-contrast imaging, hard and mid-range fluorescence spectroscopy, and
small-angle and ultra-small angle x-ray scattering. These techniques are
expanding the range of possible environments in which fluid mechanics
experiments can be conducted. They provide an opportunity to gain new
insight into the underlying physics of multi-phase flows.
Dr. Daniel Duke received his PhD in Mechanical Engineering from Monash
University in 2013, studying the aerodynamic breakup of liquid sheets.
During his PhD, Daniel spent two years in the United States on a Fulbright
Scholarship, working at the Advanced Photon Source at Argonne National
Laboratory. He joined a research group that was developing methods of using
synchrotron radiation to study the structure of high-pressure diesel fuel
injection sprays. After graduation, Daniel returned to the US as a postdoc
and spent three years at the synchrotron developing novel x-ray measurement
techniques for cavitating flows, multi-jet sprays and flash-evaporating
medical sprays. Daniel returned to Australia in 2017 as an ARC DECRA Fellow
in the Department of Mechanical & Aerospace Engineering at Monash. His
current work concerns the development of optical and x-ray diagnostics for
pharmaceutical sprays.
Stability and transition of natural convection flow in differentially heated cavities
Steve Armfield
University of Sydney
3.30pm Friday 4 May 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Natural convection flow in a differentially heated square cavity has been
widely studied, providing a canonical representation of a large range of
buoyancy driven flows. In the standard configuration one sidewall is heated,
the opposing sidewall cooled, with all other walls, ceiling and floor
adiabatic. The flow consists of natural convection boundary layers forming
on the heated/cooled walls, entraining fluid from, and discharging to, the
stratified interior. The overall flow acts to transport heat from the heated
to the cooled wall, with the details of the flow depending on the
temperature difference between the sidewalls, typically characterised by a
Rayleigh (or Grashof) number, and on the Prandtl number of the fluid.
Start-up, transition and full development have been extensively investigated
showing increasingly unsteady and complex behaviour with increasing Rayleigh
number. Early results on the basic flow structure and stability properties,
together with the nature and Prandtl number dependence of the transition to
chaotic flow at full development, will be reviewed. Recent work will be
presented on the absolute stability of the flow, together with a new
three-dimensional steady turning flow instability, in the context of the
tilted cavity.
Steve Armfield is Professor of Computational Fluid Dynamics in the School of
Aerospace, Mechanical and Mechatronic Engineering at the University of
Sydney. He completed his PhD, at the University of Sydney, in 1987, and has
held appointments at the University of Western Australia and the University
of New South Wales, as well as visiting positions at Stanford University,
Cambridge University, Saitama University, Tohoku University and Auckland
University. His research is focused on stability, transition and mixing in
buoyant and stratified flows.
Nonlinear Tollmien–Schlichting waves in a high-speed channel flow
Kengo Deguchi
Monash University
3.30pm Friday 20 April 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Plane Poiseuille flow has long served as the simplest testing ground for
Tollmien–Schlichting wave instability. The aim of this talk is to give
a comprehensive comparison of equilibrium Tollmien–Schlichting wave
solutions arising from new high-resolution Navier–Stokes calculations
and the corresponding predictions of various large-Reynolds-number
asymptotic theories developed in the last century, such as double-deck
theory, viscous nonlinear critical layer theory and strongly nonlinear
critical layer theory. In the relatively small to moderate amplitude regime,
the theories excellently predict the behaviour of the numerical solutions at
Reynolds numbers of order 106 and above, whilst for larger
amplitudes the computations suggest the need for further asymptotic theories
to be developed.
Kengo Deguchi is currently a lecturer in School of Mathematics at Monash
University. He obtained his PhD in 2013 at Kyoto University and then held a
research associate position at Imperial College London before moving to
Melbourne in 2016. He is interested in mathematical fluid dynamics of high
speed flows, in particular those using the method of matched asymptotic
expansions and dynamical systems theory.
Turbulent channel flow in the low polymer drag reduction regime
John Elsnab
University of Melbourne
3.30pm Friday 13 April 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Streamwise velocity profiles and their wall-normal derivatives were used to
investigate the properties of turbulent channel flow in the low polymer drag
reduction (DR) regime, DR = 6.5% to 26%. Streamwise velocity data were
obtained over a friction Reynolds number ranging from 650 to 1800 using the
single velocity component version of molecular tagging velocimetry (1c-MTV).
This adaptation of the MTV technique has the ability to accurately capture
instantaneous profiles at very high spatial resolution (> 850 data points
per wall-normal profile), and thus generate well-resolved derivative
information as well. Owing to this ability, the present study is able to
build upon and extend the recent numerical simulation analysis of White
et al. (J. Fluid Mech., vol. 834, 2018, pp. 409–433)
that examined the mean dynamical structure of polymer drag reduced channel
flow at friction Reynolds numbers up to 1000. Consistently, the present mean
velocity profiles indicate that the extent of the logarithmic region
diminishes with increasing polymer concentration, while statistically
significant increases in the logarithmic profile slope begin to occur for
drag reductions less than 10%. Profiles of the streamwise velocity r.m.s.
indicate that reductions in drag correlate with the location of the maximum
moving farther from the wall and increasing in magnitude. Similarly, with
increasing drag reduction, the profile of the combined Reynolds and polymer
shear stress exhibits a decrease in its maximum value that also moves
farther from the wall. Correlations are presented that estimate the location
and value of the maximum r.m.s. streamwise velocity and combined Reynolds
and polymer shear stress. Over the range of DR investigated, these effects
consistently exhibit approximately linear trends with increasing DR. The
present measurements allow reconstruction of the mean momentum balance (MMB)
for channel flow, which provides further insights regarding the physics
described in the study by White et al. (2018). In particular, the
present findings support a physical scenario in which the self-similar
properties on the inertial domain identified from the leading order
structure of the MMB begin to detectably and continuously vary for drag
reductions less than 10%.
John Elsnab received his PhD from the University of Utah in 2008 and has
been a Research Fellow at the University of Melbourne since 2011.
Illuminating the mechanics of relaminarization and roughness induced transition–a vorticity perspective
Garry Brown
Princeton University
3.30pm Friday 6 April 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
There is a long history over more than a century of experiments on turbulent
shear flows. It is now more than 100 years since Taylor (1915) first drew
attention to the connection between the transport of vorticity and the
Reynolds stress. The relationship is considered in detail but in a plane,
wall-bounded shear flow, such as channel flow, it is simply
(∂/∂y) <−u'v'>
= <v'ω'z>
− <w'ω'y>.
The long history of the 'turbulence problem' can be partly explained by the
central role of structure, or of the mechanics of the unsteady vorticity. A
simple example describes the two very different perspectives provided by a
vorticity transport and a Reynolds stress perspective. Results for free
turbulent shear flows and wall-bounded turbulent shear flows, from a
vorticity transport perspective, are presented.
The flux of vorticity across a channel is constant. Near one wall the
transfer from viscous stress to Reynolds stress is inextricably linked to
the transport of vorticity and the dominant turbulent vorticity transport is
<w'ω
y'>. The origin of this correlation, its role as
a counter gradient vorticity flux, the statistical behavior and the physical
explanation for its strongly asymmetrical PDF are discussed. The sources,
transport and dissipation of both ω
x2 and
ω
y2 are described and quantified and their
central role in the correlation, <w'ω
y'>, is shown.
By contrast for the outer flow the dominant vorticity transport is
<v'ω
z'> and its necessary connection, at high
Reynolds number, with <w'ω
y'> raises important
'vorticity structure' questions.
These results are used to explain recent numerical results on
re-laminarization and roughness induced transition. The first has been in
collaboration with ON Ramesh and his group at IISc (Bangalore) and the
second with David Goldstein and Saikishan Suryanarayanan at UT Austin.
Relaminarization in a strongly favourable pressure gradient followed by
re-transition: skin friction coefficient and wall shear stress versus
distance downstream.
In important respects they seem opposite sides of the same coin. A vorticity
perspective which has been enabled by numerical simulation and the
calculation of vorticity transport in both cases sheds light on puzzling
aspects of the mechanics. It offers a perspective on the mechanics of
turbulent shear flows in general and provides a basis for a renewed
emphasis on vorticity transport, as first proposed by GI Taylor in
1915.
Garry Brown is the Emeritus Robert Porter Patterson Professor of Engineering
at Princeton University. He received a first class Honors Degree in
Engineering from the University of Adelaide in 1964, was awarded a Rhodes
scholarship, completed his D.Phil at Oxford and was then a research
fellow/senior research fellow at GALCIT, Caltech. In 1971 he returned to the
University of Adelaide and in 1978 returned to Caltech as full professor. He
was asked to serve as Director of the Australian Aeronautical Research
Laboratory and held this position from 1981–1990 after which he joined
the faculty at Princeton, serving as Chair of the Department of Mechanical
and Aerospace Engineering from 1990 to 1998.
His best known work is in the study of turbulence. Fifty years after the
inception of the Journal of Fluid Mechanics, his 1974 paper with Professor
Roshko "On density effects and large structure in turbulent mixing layers,"
was the most frequently cited paper in the history of the journal. Since
joining Princeton he has explored new research horizons while continuing
his abiding interest in turbulence.
He has also made significant contributions, as a consultant to the American
aerospace industry, that include the root cause of failure and redesign of
the solid rocket motor for the Titan IV, the cause of early failure and
development of the thrust-vectoring system for AIM-9X and the resolution of
critical issues for Tactical Tomahawk and for the Standard Missile-3
Programs. He played a leading role in the failure investigation and redesign
of early air-cooled test cells for the after-burning F100 engine.
He is a Fellow of the Institution of Engineers of Australia, Fellow of the
American Physical Society, and a Fellow of the AIAA.
Making a LIST and checking it twice: Length scales of instabilities and stratified turbulence
Colm-cille P. Caulfield
BP Institute and DAMTP, University of Cambridge
3.30pm Friday 23 March 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Stratified shear flows, where the `background' velocity and density
distribution vary over some characteristic length scales, are ubiquitous in
the atmosphere and the ocean. At sufficiently high Reynolds number, such
flows are commonly believed to play a key role in the transition to
turbulence, and hence to be central to irreversible mixing of the density
field. Parameterizations of such irreversible mixing within larger scale
models of the ocean in particular is a major area of uncertainty, not least
because there is a wide range of highly scattered and apparently
inconsistent experimental and observational data. It is becoming
increasingly appreciated that appropriately defined characteristic length
scales of the flow are critically important to all stages of the flow's
evolution, and that such data scatter is associated with differing length
scales being important in different experiments and observations. Here, I
review some of the recent progress using modern mathematical techniques in
developing understanding of instability, transition, turbulence and mixing
in stratified shear flows, focussing in particular on the crucial role of
various length scales. I highlight certain non-intuitive aspects of the
subtle interplay between the ostensibly stabilizing effect of stratification
and destabilizing effect of velocity shear, especially when the density
distribution has layers, i.e. relatively deep and well-mixed regions
separated by relatively thin `interfaces' of substantially enhanced density
gradient.
Colm-cille P. Caulfield is Professor of Environmental and Industrial Fluid
Dynamics at the University of Cambridge, where he is a member of both the
BP Institute and the Department of Applied Mathematics and Theoretical
Physics. Before taking up his position in Cambridge in 2005, he also held
faculty positions in Environmental Engineering at the University of
California, San Diego, and in Mathematics at the University of Bristol. His
research focuses on stability, transition, turbulence and mixing in
environmental and industrial flows, particularly where density differences
play a dynamically significant role. He is an associate editor of the
Journal of Fluid Mechanics (Rapids).
Turbulent–laminar patterns
Laurette Tuckerman
CNRS/ESPCI Paris |
Website
3.30pm Friday 16 March 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The transition to turbulence is characterized by coexistence of laminar and
turbulent regions. In plane Couette and Poiseuille flow, this coexistence
takes the form of statistically stationary alternating oblique bands of
turbulent and laminar flow whose wavelength and orientation with respect to
the streamwise direction are fixed. Since the wavelength of these
astonishing patterns is much larger than the gap, they were first discovered
in very large aspect ratio experiments. We study these patterns via full
direct numerical simulation and reduced models. This is joint work with Mat
Chantry and Dwight Barkley.
Laurette Tuckerman is a senior researcher at the CNRS (Centre National de
la Recherche Scientifique) at the ESPCI (Ecole Superieure de Physique et de
Chimie Industrielles) in France. Prior to moving to France, she was on the
mathematics faculty of the University of Texas at Austin and she obtained
her bachelors and PhD from Princeton and MIT, respectively. She studies
hydrodynamic instabilities using the methods of computational fluid dynamics
and of bifurcation theory. She has studied spherical, plane, and
Taylor–Couette flow; Rayleigh–Bénard, Marangoni, and
binary fluid convection; and the Eckhaus and Faraday instabilities. She is a
Fellow of the American Physical Society and of Euromech.
Feedback mechanisms in high-speed jet resonance
Daniel Edgington-Mitchell
Monash University
3.30pm Friday 9 March 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
High-speed jets show a proclivity for self-excitation across a range of
operating conditions. This resonant behaviour is the result of a number of
complex fluid mechanic and aeroacoustic phenomena. The feedback cycle can
typically be broken into four discrete components:
1) A receptivity process in the near-nozzle shear layer, where an upstream
propagating wave produces a perturbation.
2) The unstable growth of this perturbation into a downstream-propagating
hydrodynamic wave.
3) Some downstream interaction of this hydrodynamic wave with shocks or
solid objects that produces an upstream-propagating wave.
4) The upstream propagation of this wave to the near-nozzle region.
This talk will consider current developments in understanding of these four
components of resonance mechanisms in shock-containing supersonic jets: free
jets, multi-jets and impinging jets. Recent developments in understanding of
the downstream wavemaker, and the upstream-propagating wave will be
discussed, understanding that has been achieved through a combination of
experimental measurement and the application of stability theory.
Dr Daniel Edgington-Mitchell is a Senior Lecturer in Monash University's
Department of Mechanical and Aerospace Engineering, where he works in the
Laboratory for Turbulence Research in Aerospace and Combustion. His research
focus is the study of compressible and multiphase fluid mechanics using a
primarily experimental approach. He maintains a website with some pretty
pictures of fluid flow at
daniel.edgington-mitchell.com.
Advanced numerical methods for fluid-structure interactions and their applications
Fangbao Tian
University of New South Wales Canberra
3.30pm Friday 2 March 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
This talk will introduce three versions of immersed boundary methods for a
variety of fluid-structure interaction (FSI) problems in biological flows,
energy harvester and hypersonic flows. The fundamental idea of the immersed
boundary method is to apply a source term into governing equations, which
are discretised on Cartesian mesh, to approximately achieve the boundary
conditions. Recently, immersed boundary method has been incorporated into
the second-order finite difference method (for incompressible FSI),
high-order WENO scheme (for compressible FSI) and lattice Boltzmann method
(for incompressible moderate and high Reynolds number FSI). New elements
including adaptive mesh, multiphase flows and non-Newtonian rheology have
been considered. Validations are presented to show the accuracy and
efficiency of these methods. Applications of the methods are briefly
introduced.
Dr Fangbao Tian is a Senior Lecturer in the School of Engineering and
Information Technology of UNSW, Canberra. His research focuses on numerical
methods for fluid-structure interaction and complex flows, as well as their
applications. He was awarded a PhD in Engineering Mechanics in June 2011 by
the University of Science and Technology of China. In September 2011, he
joined the Computational Flow Physics Laboratory at Vanderbilt University,
USA, as a Postdoctoral Researcher. In August 2013, he moved to SEIT as a
Research Associate and got a Lecturer position here in 2014. He was
promoted to Senior Lecturer in 2017.
What does a JFM Editor look for when assessing a paper?
Ivan Marusic
University of Melbourne
3.30pm Friday 23 February 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Completion: Experimental factors influencing the quality of PIV results
Kristian Grayson
University of Melbourne
4pm Wednesday 14 February 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Experimental error sources have the potential to generate the bulk of
errors encountered in a PIV experiment. Therefore, thorough consideration
and analysis of these error causes, and informed modifications to the
experimental setup can yield significant improvements to the quality of a
measurement. This talk will cover a series of important, practical
considerations to the setup of PIV experiments (as well as other
laser-based flow visualisation techniques), which can greatly enhance the
performance and accuracy of results. The matching and alignment of laser
light sheets is one (often underappreciated) factor which can be crucial to
achieving high quality PIV measurements. Additionally, an awareness of a
laser's stability and transient warm up characteristics is also beneficial
when performing laser experiments. The emphasis of this presentation will
be on the practical actions an experimentalist can take to avoid these
issues.
On the fundamentals of Rayleigh–Taylor instability and interfacial Rayleigh–Taylor mixing
Snezhana I. Abarzhi
University of Western Australia
3.30pm Friday 9 February 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Rayleigh–Taylor instability (RTI) develops when fluids of different
densities are accelerated against their density gradient. Extensive
interfacial mixing of the fluids ensues with time. The Rayleigh–Taylor
(RT) mixing controls a broad range of processes in nature and technology.
Examples include inertial confinement fusion, core-collapse supernova,
stellar and planetary convection, reactive and super-critical fluids, fossil
fuel recovery, and nano-electronics. In this work, we focus on the classical
problem RT mixing induced by variable acceleration with power law time
dependence. By applying group theory, we find symmetries, invariants,
scaling, correlations and spectra of the RT mixing, and quantify its
sensitivity to the initial conditions. In a broad range of the acceleration
parameters, critical points are identified at which the RT dynamics is
ballistics, quasi-Kolmogorov, steady flex, diffusive, and dissipative. For
super-ballistics and super-Kolmogorov dynamics, RT mixing has greater degree
of order when compared to canonical turbulence. For up-steady-flex and
super-diffusion—larger velocity fluctuations occur at larger scales,
whereas for sub-diffusion and dissipation—larger velocities correspond
to smaller scales. The properties of RT mixing depart substantially from
those of canonical turbulence thus opening new perspectives for better
understanding and control of RT dynamics in nature and technology.
Snezhana Abarzhi works at the University of Western Australia as Professor
and Chair of Applied Mathematics. Her research interests are in Applied
Mathematics (applied analysis, partial differential equations, dynamical
systems) and in Theoretical Applied and Physics (plasmas, fluids,
materials). The focus of Dr. Abarzhi's research is on Rayleigh–Taylor
instabilities and interfacial mixing. Her contribution to this field is in
rigorous physics-based theory for fundamentals of unstable interfacial
dynamics.
Direct numerical simulation of internal compressible flows at high Reynolds number
Davide Modesti
University of Melbourne
3.30pm Friday 2 February 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Instantaneous flow field for square duct flow at friction Reynolds number
Re
τ = 1000. Streamwise velocity contours in the cross-stream
(yz) and wall-parallel (at y
+ = z
+ = 15) planes are
shown. The mean cross-flow structure is also visualized using streamfunction
isolines.
The talk will focus on the results of a recently developed DNS database
which includes plane channel, pipe and duct flow, across a wide range of
Mach (M
b = 0.2–3), and Reynolds numbers
(Re
τ = 180–1000) (Modesti & Pirozzoli,
J. Sci. Comput., 2017; Modesti & Pirozzoli, Int. J. Heat Fluid Flow,
2016). The effect of compressibility on the
mean flow statistics will be discussed for plane channel and pipe flow,
focusing on transformations which allow to map the compressible flow
statistics onto the incompressible ones. The talk will also address some
recent findings on the role of secondary motions in square duct flow and
their effect on the mean velocity field (Pirozzoli, Modesti, Orlandi &
Grasso, J. Fluid Mech., 2018). Despite their effect of
redistributing the wall shear stress along the duct perimeter, we find that
secondary motions do not have large influence on the mean velocity field,
which can be characterized with good accuracy as that resulting from the
concurrent effect of four independent flat walls, each controlling a quarter
of the flow domain. Further insight on the role of these motions is gained
by performing numerical experiments in which secondary flows are
artificially suppressed, revealing that they act as a sort of
self-regulating mechanism of turbulence which acts to mitigate the effect of
the corners.
Davide Modesti is postdoc at the University of Melbourne. He earned a PhD in
Theoretical and Applied Mechanics from La Sapienza Università di
Roma in 2017, where he carried out direct numerical simulations (DNS) of
compressible wall-bounded flows at high Reynolds number. After completing
his PhD he has been postdoc at DynFluid laboratory (ENSAM-CNAM) in Paris,
where he studied secondary motions in rectangular duct flow using DNS. Since
January 2018 he joined the Fluid Mechanics Research Group at the University
of Melbourne.
Thermoacoustic oscillations in annular combustors: symmetry, eigenstructure, perturbation methods, and nonlinear phenomena
Jonas Moeck
Technical University of Berlin and Norwegian University of Science and Technology
3.30pm Tuesday 19 December 2017
Old Metallurgy Masters Seminar Room 1 (Room 103, Bldg 166)
Thermoacoustic instabilities frequently appear in various combustion systems
in the form of high-amplitude pressure oscillations. This undesirable
dynamic phenomenon originates from the interaction of flame oscillations and
the acoustic modes of the combustion chamber. It has been particularly
plaguing for the development of high-efficiency, low-emission gas turbine
technology. After a brief introduction to the topic, I will discuss some
aspects that are specific to annular combustion chambers, as they are found
in aeroengines and in most gas turbines for power generation. These
combustors exhibit special dynamical features associated with their
discrete rotational symmetry. After introducing the key aspects of the
linear eigenstructure of this type of system, I will present some recent
tools for stability assessment, uncertainty quantification, optimization,
and nonlinear analysis of annular thermoacoustic systems.
Jonas Moeck is an Associate Professor at the Technical University Berlin and
the Norwegian University of Science and Technology. He received engineering
degrees from the University of Michigan and the Technical University Berlin,
a PhD from the latter institution and was a postdoctoral scholar at
Laboratoire EM2C, Ecole Centrale Paris. His research interests include flame
dynamics, combustion control, low-order modeling and stability analysis,
pulsed detonation, and plasma-assisted combustion.
Color of turbulence
Mihailo Jovanovic
University of Southern California
3.30pm Monday 18 December 2017
Old Metallurgy Masters Seminar Room 1 (Room 103, Bldg 166)
This talk describes how to account for second-order statistics of turbulent
flows using low-complexity stochastic dynamical models based on the
linearized Navier-Stokes (NS) equations. The complexity is quantified by the
number of degrees of freedom in the linearized evolution model that are
directly influenced by stochastic excitation sources. For the case where
only a subset of correlations are known, we develop a framework to complete
unavailable second-order statistics in a way that is consistent with
linearization around turbulent mean velocity. In general, white-in-time
stochastic forcing is not sufficient to explain turbulent flow statistics.
We develop models for colored-in-time forcing using a maximum entropy
formulation together with a regularization that serves as a proxy for rank
minimization. We show that colored-in-time excitation of the NS equations
can also be interpreted as a low-rank modification to the generator of the
linearized dynamics. Our method provides a data-driven refinement of models
that originate from first principles and it captures complex dynamics of
turbulent flows in a way that is tractable for analysis, optimization, and
control design.
Mihailo Jovanovic
(
http://ee.usc.edu/mihailo/) is a
professor in the Ming Hsieh Department of Electrical Engineering and the
founding director of the Center for Systems and Control at the University of
Southern California. He was a faculty in the Department of Electrical and
Computer Engineering at the University of Minnesota, Minneapolis, from
December 2004 until January 2017, and has held visiting positions with
Stanford University and the Institute for Mathematics and its Applications.
His current research focuses on the design of controller architectures,
dynamics and control of fluid flows, and fundamental limitations in the
control of large networks of dynamical systems. He serves as the Chair of
the APS External Affairs Committee, an Associate Editor of the SIAM Journal
on Control and Optimization and of the IEEE Transactions on Control of
Network Systems, and had served as an Associate Editor of the IEEE Control
Systems Society Conference Editorial Board from July 2006 until December
2010. Prof. Jovanovic is a fellow of APS and a senior member of IEEE. He
received a CAREER Award from the National Science Foundation in 2007, the
George S. Axelby Outstanding Paper Award from the IEEE Control Systems
Society in 2013, and the Distinguished Alumni Award from UC Santa Barbara
in 2014.
Identification, decomposition and analysis of dynamic large-scale structures in turbulent Rayleigh–Bénard Convection
Yulia Peet
Arizona State University
11.30am Friday 15 December 2017
Old Metallurgy Masters Seminar Room 1 (Room 103, Bldg 166)
At high Rayleigh numbers in moderate aspect-ratio cylindrical domains
turbulent Rayleigh–Bénard convection (RBC) exhibits coherent
large-scale motions that organize themselves into a collection of
three-dimensional "roll cells". In the current talk, we present the
results and analysis of Direct Numerical Simulation of the RBC in a
cylindrical domain with a 6.3 aspect ratio and the Rayleigh number of
9.6×107. The analysis of the long-time data series that are
collected for the duration of over 100 eddy turnovers shows that the spatial
organization of the roll cells in the investigated domain can be well
described by the azimuthal Fourier modes. A hub-and-spoke mode-3 pattern
first emerges and dominates the flow for the first 20 eddy turnovers, which
then transitions into a mode-2 pattern that persists for the remainder of
the simulations. A spatial inhomogeneity of the observed mode-3 and mode-2
structures is investigated. A conclusion follows that the cylindrical
geometry constraint applies a "squeezing" effect to the large-scale
structures, which forces them to align with a strong azimuthal
periodicity.
Yulia Peet is an Assistant Professor of Mechanical and Aerospace Engineering
at the School for Engineering of Matter, Transport and Energy at Arizona
State University since Fall 2012. Her Ph.D. degree is in Aeronautics and
Astronautics from Stanford (2006), M.S. and B.S. degrees are from Moscow
Institute of Physics and Technology (1999 and 1997). Her previous
appointments include a Postdoctoral position at the University of Pierre and
Marie Curie in Paris in 2006–2008, and a dual appointment as an NSF
Fellow at Northwestern and Assistant Computational Scientist at Argonne
National Laboratory in 2009–2012. Her research interests include
computational methods and high-performance computing, fluid mechanics and
turbulence, with applications in wind energy, aerospace, and biological
fluid mechanics.
Wind farm modeling and control for power grid support
Dennice Gayme
Johns Hopkins University
3.30pm Monday 11 December 2017
Old Metallurgy Masters Seminar Room 1 (Room 103, Bldg 166)
Traditional wind farm modeling and control strategies have focused on layout
design and maximizing wind power output. However, transitioning into the
role of a major power system supplier necessitates new models and control
designs that enable wind farms to provide the grid services that are often
required of conventional generators. This talk introduces a model-based wind
farm control approach for tracking a time-varying power signal such as a
frequency regulation command. The underlying time-varying wake model extends
commonly used static models to account for wake advection and lateral wake
interactions. We perform numerical studies of the controlled wind farm using
a large eddy simulation (LES) with actuator disks as a wind farm model. Our
results show that embedding this type of dynamic wake model within a
model-based receding horizon control framework leads to a controlled wind
farm that qualifies to participate in markets for correcting short-term
imbalances in active power generation and load on the power grid (frequency
regulation). We also demonstrate that explicitly accounting for the
aerodynamic interactions between turbines within the proposed control
strategy yields large increases in efficiency over prevailing approaches by
achieving commensurate up-regulation with smaller derates (reductions in
wind farm power set points). This potential for derate reduction has
important economic implications because smaller derates directly correspond
to reductions in the loss of bulk power revenue associated with
participating in regulation markets.
Dennice F. Gayme is an Assistant Professor and the Carol Croft Linde Faculty
Scholar in Mechanical Engineering at the Johns Hopkins University. She
earned her B. Eng. & Society from McMaster University in 1997 and an
M.S. from the University of California at Berkeley in 1998, both in
Mechanical Engineering. She received her Ph.D. in Control and Dynamical
Systems in 2010 from the California Institute of Technology, where she was
a recipient of the P.E.O. scholar award in 2007 and the James Irvine
Foundation Graduate Fellowship in 2003. Her research interests are in
modeling, analysis and control for spatially distributed and large-scale
networked systems in applications such as wall-bounded turbulent flows,
wind farms, power grids and vehicular networks. She was a recipient of the
JHU Catalyst Award in 2015, a 2017 ONR Young Investigator award, and an NSF
CAREER award in 2017.
Modelling the infra-red signatures of aircraft and missiles: current and future practice
Nigel Smith
Defence Science Technology Group
3.30pm Friday 8 December 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The appropriate application of fluid mechanics modelling is essential to
successfully predicting the infra-red signatures of aircraft and missiles.
It is, however, but one element of a larger framework of necessary models.
This talk will provide a qualitative understanding of the key phenomena
associated with the IR signatures of airborne systems, the physical
processes to be modelled and practical issues arising. The roadmap for
future development will be outlined.
Nigel Smith completed a PhD in Mechanical Engineering in 1994 at the
University of Sydney. The topic of this PhD and subsequent postdoctoral
fellowship at Stanford University and the NASA Ames Research Center was the
numerical modelling of turbulent combustion. He joined DST Group in 1996,
and has since worked on combustion, rocket and air-breathing propulsion, and
infra-red signatures. From 2009 he has led the Infrared Signatures and
Aerothermodynamics Group (IRSA) in Aerospace Division. IRSA is an integrated
team responsible for measuring, modelling and managing the signatures of
aircraft and other systems for Defence.
Advanced understanding of turbulent combustion processes
Assaad Masri
University of Sydney
12pm Friday 17 November 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
This seminar is jointly organised with the Thermodynamics Research Group. For more information, see:
Thermodynamics seminars.
Local transport of passive scalar released from a point source in a turbulent boundary layer
Kapil Chauhan
University of Sydney
3.30pm Friday 10 November 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Simultaneous measurements of velocity and concentration fluctuations for a
horizontal plume released at eight different locations within a turbulent
boundary layer (TBL) will be discussed. Statistics based on
cross-correlation of velocity and concentration reveal the organisation of
flow structures and the meandering plume. The time-averaged streamwise
concentration flux is found to be positive and negative respectively, below
and above the plume centreline. This behaviour is a result of wall-normal
velocity fluctuations and Reynolds shear stress that play a dominant role in
the vertical spread of scalar plume. Results of cross-correlation
coefficient show that high- and low-momentum regions have a distinctive role
in the transport of passive scalar. Above the plume centreline, low-speed
structures have a lead over the meandering plume, while high-momentum
regions are seen to lag behind the plume below its centreline. Based on
these observations, a physical model is proposed for the relative
arrangement of a passive scalar plume with respect to large-scale structures
in the flow.
Dr. Kapil Chauhan is a lecturer in the School of Civil Engineering at The
University of Sydney where he undertakes research within the Centre forWind,
Waves, and Water and industry-linked projects in the Boundary Layer Wind
Tunnel. Dr. Chauhan's research examines how fluids such as water and air
flow over various surfaces under different conditions. In the BLWT, he has
utilized his expertise in turbulent boundary layers and experimental methods
to offer unique measurement capabilities for wind engineering applications.
His research interests include wind energy, entrainment in boundary layers,
scalar transport and natural convection. Dr. Chauhan graduated with a PhD
from Illinois Institute of Technology, Chicago in 2007 and was a
post-doctoral research fellow at University of Melbourne from 2009 to
2014.
The fluid mechanics of microbial communities
Douglas Brumley
School of Mathematics and Statistics, University of Melbourne |
Website
3.30pm Friday 3 November 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Fluid mechanics at the microscale governs a myriad of physical, chemical and
biological processes. In this talk I will discuss several examples in which
the ability to deconstruct complex biological systems and confine, control
and visualise them, has enabled the development of new mathematical
frameworks, from the active search strategies of marine bacteria to the
dynamics of invading pathogens in the intestine. In each case, I will
highlight how access to modern experimental results can uniquely inform the
development of models with far-reaching ecological insights.
Douglas Brumley is a Lecturer in Applied Mathematics at The University of
Melbourne. Before his current position, he was a Postdoctoral Researcher and
Fellow of the Human Frontier Science Program, working with Professor Roman
Stocker at MIT and ETH Zurich. He completed his PhD in the Department of
Applied Mathematics and Theoretical Physics (DAMTP) at The University of
Cambridge, under the supervision of Professor Timothy Pedley, FRS. During
this time, Douglas was a Gates Cambridge Scholar and External Research
Scholar at Trinity College. Douglas' research integrates experimental
approaches and mathematical models to investigate microscale fluid flows in
biology.
Completion: Drag reduction via manipulation of large-scale coherent structures in a high Reynolds-number turbulent boundary layer
Reza Abbassi
University of Melbourne
3.30pm Friday 27 October 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The large-scale coherent structures in the outer region of a
high-Reynolds-number turbulent boundary layer have been shown to be highly
energetic with an influence that extends down to the wall and thus affecting
skin friction. These structures possess bilateral characteristics; their
instantaneous streamwise velocity are either higher or lower than the mean
streamwise velocity at each wall-normal height, with these high- and
low-speed regions accompanied by respective down- and up-ward wall-normal
velocity components. In a conditional sense, counter-rotating roll modes are
manifested in the spanwise-wall-normal planes.
In this talk, results of a real-time drag reduction strategy will be
presented where actuation involves using wall-normal jets. For an actuation
strategy where the jets are synchronized with the high-speed regions results
in a reduction of the energy associated with the large-scale structures in
the outer region (∼30% reduction of large-scale spectral energy was
observed in the log-region). Additionally, a maximum mean wall-shear stress
reduction of 3.2% was measured at 1.6 boundary layer thicknesses downstream
of the actuators. Additional measurements involving random firing of the
jets, and synchronisation with low-speed events show that the
above-mentioned results are not a by-product of the injection of the
wall-normal jet airflow into the turbulent boundary layer, rather it is due
to the implicit synchronization with the down-wash sections of the
counter-rotating roll modes which accompany the high-speed regions and led
to an opposition mechanism of the control scheme.
Flow external to a rotating torus (or a sphere)
Sophie Calabretto
Macquarie University
3.30pm Thursday 26 October 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The unsteady flow generated due to the impulsive motion of a torus or sphere
is a paradigm for the study of many temporally developing boundary layers.
The boundary layer is known to exhibit a finite-time singularity at the
equator. We present results of a study that focuses upon the behaviour of
the flow after the onset of this singularity. Our computational results
demonstrate that the singularity in the boundary layer manifests as the
ejection of a radial jet. This radial jet is preceded by a toroidal starting
vortex pair, which detaches and propagates away from the sphere. The radial
jet subsequently develops an absolute instability, which propagates upstream
towards the sphere surface.
Sophie Calabretto is a Lecturer in Applied Mathematics at Macquarie
University. Her research in fluid dynamics seeks to understand and predict
the behaviour of rotating fluids, exploring fundamental questions in fluid
physics, with the potential to impact fields as diverse as aerodynamics and
climate science.
Nonlinear internal tide dynamics and diapycnal mixing on continental shelves
Nicole Jones
University of Western Australia
3.30pm Friday 20 October 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The coastal shelf in Northwest Australia is a region of strong nonlinear
internal wave generation and dissipation that results from strong tidal
flows. Here we focus on a combination of moored and ship-based observations
collected in 100 m of water 4–22 April 2012. The moored
instrumentation observed both mean vertical temperature and velocity
structure as well as turbulence quantities. The nonlinear internal wave
(NLIW) packets were characterised by isotherm displacements of up to 60 m,
occurred once per semi-diurnal tidal cycle and generally persisted for 4 h,
with periods ranging from 10–30 minutes. The NLIWs were not
consistently phase-locked to either the surface tide or internal tide. The
largest turbulent overturns observed coincided with the downward isotherm
propagation phase of each of the NLIWs within a packet. The observed
diffusivity spanned six orders of magnitude and the median value was over
four orders of magnitude greater than molecular diffusion. The highest
values of diapycnal diffusivity were event driven, for example, during the
occurrence of nonlinear internal wave packets when the stratification
weakened due to straining of the background density gradient and there were
comparatively large turbulent overturns. The diffusivity was often larger at
the mid-water column compared with the near-bed, due to isopycnal straining
and shear. Our direct estimates of diffusivity demonstrate that using the
Osborn model with a constant mixing efficiency can both vastly over-predict
and under-predict the diffusivity. Our diffusivity estimates can be used to
improve predictions of processes such as the transport of nutrients,
sediment and pollutants.
Dr Jones graduated from Stanford University with a PhD in Civil and
Environmental Engineering in 2007. She is currently a Senior Lecturer at the
University of Western Australia. Dr Jones' research focus is environmental
and geophysical fluid dynamics, in particular the interaction between the
physics and biogeochemistry in natural aquatic environments. She uses a
combination of field observations and numerical modelling to study topics
such as: The elucidation of internal wave generation, propagation and
dissipation; The role of complex topography in circulation and mixing in a
macro-tidal environment; Ocean mixing; The role of non-linear internal waves
in stimulating primary productivity; The ocean response to tropical cyclone
forcing; The influence of whitecapping waves on the vertical structure of
turbulence in shallow water environments; The hydrodynamic control of
phytoplankton loss to the benthos in estuarine environments; Plume
dispersion on fringing coral reefs; The development of field techniques for
studying environmental fluid mechanics.
Some applications of the resolvent analysis
Paco Gómez
RMIT University
3.30pm Friday 13 October 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
In the first part of the talk, I will present a reduced-order model for
unsteady flows arising from the resolvent analysis of McKeon & Sharma
(J. Fluid Mech., 2010). The inputs required for the model are the mean flow
field and a small set of velocity time-series data obtained at isolated
measurement points, which are used to fix relevant frequencies, amplitudes
and phases of a limited number of resolvent modes that, together with the
mean flow, constitute the reduced-order model. Some applications of the
model include the identification of relevant flow structures, the
reconstruction of dynamics and the estimation of unsteady aerodynamic
forces. The technique will be applied to derive a model for three different
flows: (i) an unsteady three-dimensional flow in a lid-driven cavity,
(ii) an oscillatory flow past a square cylinder and (iii) a turbulent pipe
flow.
The second part will explore how to control self-sustained oscillations
using a data-driven decomposition based on the resolvent analysis. The
decomposition consists of a temporal correlation between POD modes of
fluctuating velocity and nonlinear forcing, and its physical interpretation
is the simultaneous identification of the most energetic self-sustained
motions in the flow and the corresponding forcing that excite them.
Applications to flow control strategies in which a suppression of the
forcing inhibits the vortex shedding past 2D and 3D bluff bodies will be
shown.
Francisco (Paco) Gómez is a Lecturer in Computational Aerodynamics at
RMIT University. He obtained a PhD in Aerospace Engineering from the
Technical University of Madrid and he was a Postdoctoral Research Fellow at
Monash University. His research interests include flow instability, flow
control and reduced-order modelling.
Secondary eyewall formation in tropical cyclones
Jeff Kepert
Head, High Impact Weather Research, Bureau of Meteorology
3.30pm Friday 6 October 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Roughly half of all intense tropical cyclones experience an eyewall
replacement cycle. In these events, a new eyewall forms concentrically
around the original one. This secondary eyewall develops its own wind
maximum, and both the secondary eye and its wind maximum typically intensify
and contract, whilst the original eyewall and wind maximum weaken and
eventually dissipate. Although the evolution of a storm with concentric
eyewalls is reasonably well understood, the mechanism or mechanisms by which
the outer eyewall forms remain elusive. Understanding secondary eyewall
formation is an important problem, for the subsequent eyewall replacement
cycle can significantly affect the intensity of the storm, and the formation
process and replacement cycle are usually associated with a major expansion
of the outer wind field. Both these factors significantly affect the
cyclone's impact.
We investigate a high resolution numerical simulation of an eyewall
replacement cycle. We show that horizontal convergence within the boundary
layer due to friction substantially influences the evolution of the
convection. We show how this convergence is sensitive to the details of the
vortex structure, best understood in terms of vorticity, and how it is quite
different to classical Ekman pumping. Using this theory, we present evidence
for a positive feedback involving convection, vorticity and frictional
convergence that governs the subsequent evolution of the system. In this
feedback, frictional convergence strengthens the eyewall clouds, stretching
of vortex tubes in the buoyant updrafts in those clouds increases the
vorticity, and the vorticity structure of the storm determines the strength
and location of the frictional updraft.
Dr Jeff Kepert leads the High Impact Weather research team at the Bureau of
Meteorology, which is responsible for improving understanding and prediction
severe weather in Australia, including tropical cyclones, fire weather,
severe thunderstorms and heatwaves. He is widely known for his tropical
cyclone research, particularly into the dynamics and characteristics of the
near-surface flow. More recently, he has branched out into fire weather
research, including case studies of some severe fire events, contributing to
the development of a prototype ensemble fire prediction system, and work on
coupled fire-atmosphere modelling. He has a strong interest in analysing and
quantifying uncertainties in weather forecasts, with the multiple aims of
making forecasts more useful by including error bars, improving our analysis
of the current atmospheric state, and better understanding atmospheric
dynamics.
Jeff completed his undergraduate studies at the University of Western
Australia and his postgraduate degrees at Monash University. Most of his
career at the Bureau of Meteorology has been spent in the research centre,
but he has also worked as a forecaster and in the training branch.
Transition modelling for RANS/URANS approaches and applications to turbomachinery flows
Roberto Pacciani
University of Florence, Italy
3.30pm Friday 15 September 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Current models for transition in turbomachinery boundary layers are
described in the framework of Reynolds-averaged Navier–Stokes (RANS or
URANS) description of the flow. These include the
γ–Reθ,t and laminar-kinetic-energy (LKE) based
families of models. Emphasis is put on the discussion on the way transition
mechanisms are expressed by model ingredients. Model equations are analyzed
on a consistent physical basis. The predictive quality of the models is
assessed through applications to the prediction of steady/unsteady flows in
cascades operating in low pressure turbine conditions. The strong and weak
features of each formulation are also evidenced and discussed.
After completing his graduate degree in mechanical engineering at the
University of Florence, Roberto Pacciani received his Ph.D. from the
Technical University of Bari in 1997. Since 1999, he has been a member of
the faculty of mechanical engineering at the University of Florence. He is
presently Associate Professor in the same institution. His research
interests involve the development of Computational Fluid Dynamics
methodologies with a special focus on turbomachinery design and analysis,
and particular emphasis on turbulence/transition modelling and unsteady
component interactions. Applications mainly concern the advanced aerodynamic
design of aeronautical and industrial turbomachinery.
Monte Carlo methods for oscillatory nanoscale gas flows
Daniel Rowan Ladiges
University of Melbourne
3.30pm Friday 1 September 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Gas flows generated by resonating nanoscale devices inherently occur in the
non-continuum, low Mach number regime. As the continuum assumption
underpinning the Navier-Stokes equations is violated, these flows must be
modelled using an approach that accounts for the non-continuum nature of the
gas, i.e. the Boltzmann equation. Solution of the Boltzmann equation is
difficult using standard numerical approaches–this has motivated the
development of a range of Monte Carlo methods for simulating gas flows, the
most well known of which is direct simulation Monte Carlo (DSMC).
We begin this talk with an introduction to the Boltzmann equation applied to
nanoscale flows, followed by a discussion of methods which solve this
equation using a Monte Carlo approach. We then present a frequency-domain
Monte Carlo method which may be applied to oscillatory low Mach number gas
flows. This circumvents the requirement of current Monte Carlo methods to
operate in the time-domain, providing direct access to amplitude and phase
information using a pseudo-steady algorithm. This frequency-domain method is
shown to provide a significant improvement in computational speed compared
to existing time-domain Monte Carlo methods.
Daniel received his PhD in applied mathematics from the University of
Melbourne in 2016, where he is currently a postdoctoral researcher. His
areas of research include analytic and numerical methods for solving the
Boltzmann equation, particularly in the context of nanoscale gas flows.
Coherent structures and particles in turbulent boundary layers
Ellen Longmire
University of Minnesota, USA
3.30pm Friday 18 August 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
This talk will focus on our experience employing planar and volumetric
velocimetry techniques to investigate the nature of turbulent boundary
layers and the motions of finite particles within them. Fluid velocity
fields are analyzed to quantify and understand the organization of coherent
eddies as well as their relation to regions of long streamwise coherence. In
the logarithmic region, extended packets of eddies can be tracked over
significant distances. Our efforts to manipulate the packet organization and
to understand packet recovery from perturbations will be discussed. In
addition, our first results characterizing translation and rotation of
spherical particles within the boundary layer will be presented.
Ellen Longmire received an A.B. in physics (1982) from Princeton University
and M.S. (1985) and Ph.D. (1991) degrees in mechanical engineering from
Stanford University. Prior to receiving her Ph.D., she worked as an engineer
at Hauni-Werke Koerber & Co in Germany and at Honeywell and SAIC in the
U.S. Since 1990, she has taught and directed research in the Department of
Aerospace Engineering and Mechanics at the University of Minnesota where she
holds the rank of Professor. She uses experimentation and analysis to answer
fundamental questions in fluid dynamics that affect industrial,
environmental, and biological applications. She is a Fellow of the American
Physical Society and received the UM Distinguished Women Scholars Award
(2007), the McKnight Land-Grant Professorship (1994), and the NSF National
Young Investigator Award (1994). She serves as Editor-in-Chief of
Experiments in Fluids. She previously served as Chair of the American
Physical Society Division of Fluid Dynamics (2016), member of the U.S.
National Committee on Theoretical and Applied Mechanics (2011-2015) and
Associate Editor of Physics of Fluids (2008-2013).
Completion: Sub-miniature hot-wire anemometry for high Reynolds number turbulent flows
Milad Samie
University of Melbourne
4pm Friday 11 August 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Despite several decades of research in wall-bounded turbulence there is
still controversy over the behaviour of streamwise turbulence intensities
near the wall, especially at high Reynolds numbers. Much of it stems from
the uncertainty in measurement due to finite spatial resolution.
Conventional hot-wire anemometry is limited for high Reynolds number
measurements due to limited spatial and temporal resolution issues that
cause attenuation in the streamwise turbulence intensity profile near the
wall. To address this issue we use the NSTAP (nano-scale thermal anemometry
probe) developed at Princeton University to conduct velocity measurements
in the high Reynolds number boundary layer facility at the University of
Melbourne. NSTAP is almost one order of magnitude shorter than conventional
hot-wires. This enables us to acquire fully-resolved velocity measurements
of turbulent boundary layers up to a friction Reynolds number of 20,000.
Wall-resolved large-eddy simulation of flow about smooth-walled and span-wise grooved cylinders
Dale Pullin
Graduate Aerospace Laboratories California Institute of Technology, USA
3.30pm Friday 4 August 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Wall-resolved large-eddy simulation (LES) of flow over both smooth- and
grooved-walled cylinders will be discussed. The stretched-vortex sub-grid
scale model is embedded in a general fourth-order finite-difference code
discretization on a curvilinear, body-fitting mesh. The grooved cylinder
consists of 32 equal, sinusoidal, spanwise grooves around the cylinder
circumference, each of equal height ε. The LES is first used to
investigate the effect of groove height in 0 ≤ ε/D ≤ 1/32 at
Re
D = 3.9 x 10
3. A second set of LES uses fixed
ε/D = 1/32 with 3.9 x 10
3 ≤ Re
D
≤ 6 x 10
4, the latter value reaching the transcritical range.
The presence of grooves substantially reduces the Re
D range of
the drag crisis. Both smooth-walled and grooved-wall cylinder flows exhibit
mean-flow secondary separation bubbles embedded within the large-scale,
separated flow region at subcritical Re
D. These transform to
prior separation bubbles as Re
D is increased through and beyond
the respective drag crises. For the smooth-wall flow this is associated with
local transition to turbulence and a strong drag crisis. For the
grooved-cylinder case the flow remains laminar but unsteady through its drag
crisis and into the early transcritical flow range.
This research is performed in collaboration with W. Cheng and R. Samtaney
(King Abdullah University of Science and Technology).
Dale Pullin is the Robert H. Goddard Professor at the Graduate
Aerospace Laboratories California Institute of Technology. His research
interests include computational and theoretical fluid mechanics, vortex
dynamics, compressible flow and shock dynamics, turbulence, and large-eddy
simulation of turbulent flows.
Confirmation: Development of algebraic Reynolds stress models for low pressure turbines using machine learning techniques
Harshal Akolekar
University of Melbourne
2pm Wednesday 2 August 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Enhancing the efficiency of the low pressure turbine (LPT) of an aircraft
engine leads to the reduction in specific fuel consumption and carbon
emissions. This enhancement can be achieved by accurately capturing two
important phenomena in the designing and modelling process, namely:
separation-induced transition and turbulent wake mixing. Direct numerical
simulations (DNS) offer the most accurate solution to this problem but are
still computationally expensive. On the other hand, some RANS-based
turbulence and transition models, six of which are used in this work to
analyse the T106A LPT profile, estimate the separation to some degree of
accuracy, but predict inaccurate wake-loss profiles. This is partly due to
the use of the Boussinesq approximation to derive stress-strain
relationships. An approach is therefore sought to improve the Boussinesq
relationship by the development of algebraic Reynolds stress models. Instead
of using a conventional analytical approach, this work uses an evolutionary
Gene Expression Programming algorithm (a machine learning approach) to
develop algebraic models based on reference DNS data sets. Preliminary
analysis has shown that the developed algebraic Reynolds stress models
improve the turbulent wake-mixing and consequently wake-loss profiles.
Confirmation: Turbulent flow over surfaces with spanwise heterogeneity
Dea Wangsawijaya
University of Melbourne
3.30pm Friday 28 July 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Examples of wall-bounded turbulent flows over surfaces with heterogeneous
roughness are abundant in both engineering applications and nature. A
specific case of heterogeneity is a surface with roughness variation in the
spanwise direction. Such surface generates secondary flow in the form of
roll modes along the streamwise direction. Studies regarding the behaviour
of wall-turbulent flows over spanwise heterogeneous roughness found
contradictory results in terms of the sign of the roll modes and the mean
streamwise velocity component U. The latter, as shown by a recent study by
Chung, Monty & Hutchins (2017), might be affected by the ratio of spanwise
roughness wavelength to δ. In this initial study, hot-wire
measurements were performed over surfaces with spanwise heterogeneous
roughness with a certain half-wavelength Λ, yielding a range of
Λ/δ from 0.32 to 6.50. It is found that as Λ/δ
becomes very large, secondary flows are restricted to the interface between
high and low shear stress region, leaving the high and low stress region
away from the interface to behave as if the surface becomes homogeneous
based on the local stress. Similarly, measurement results of the very small
Λ/δ test case show that secondary flows are confined within
the near-wall region. Away from the wall, flow over the small
Λ/δ case becomes spanwise homogeneous. As Λ/δ
≈ 1, U above the high and low shear stress region switches sign: U
is higher above high shear stress region and lower above low stress region.
Further analysis of 1-D energy spectra profile shows the occurrence of a
second peak in the wake region, which might be related to an instability of
secondary flows (Kevin et al. 2017).
Completion: Boundary layer and bulk behaviour in vertical natural convection
Chong Shen Ng
University of Melbourne
3.30pm Friday 21 July 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Thermal convection is ubiquitous in nature and many engineering
applications, for example, from the scale of convection in stars and in
Earth's atmosphere, down to the scale of convection-driven heating or
cooling of the built environment and in the computer that you are using to
read this text. In this research, we consider the buoyancy driven flow that
is sustained between two vertical walls, where the left wall is heated and
the right wall cooled. We refer to this setup as vertical natural
convection. Results from direct numerical simulations for Rayleigh numbers
105–109 and Prandtl number 0.709 are found to
support a generalised applicability of the Grossmann–Lohse theory for
thermal convection, originally developed for Rayleigh–Bénard
convection. Similar to Rayleigh-Bénard convection, a pure power-law
relationship between the Nusselt, Rayleigh and Prandtl numbers is not the
best description for vertical natural convection and existing empirical
relationships should be recalibrated to better reflect the underlying
physics.
In this talk, we show that for the present Rayleigh number range, the mean
laminar-like boundary layers coexist with local near-wall patches that
exhibit turbulent behaviour. Thus, the Nusselt number versus Rayleigh number
scaling relation is contaminated by dynamics of the two regions. When the
walls are removed and boundary layers omitted, the new setup mimics
turbulent bulk-dominated thermal convection and we show that the Nusselt
number versus Rayleigh number scaling relation instead follows the 1/2
power-law asymptotic scaling relation, in agreement with the theoretical
predictions of Kraichnan (Phys. Fluids, 1962, vol. 5, pp. 1374–1389)
and Grossmann and Lohse (J. Fluid Mech., 2000, vol. 407, pp. 27–56).
An extension of this result to the wall-bounded setup is discussed.
Completion: Characterisation of a microfluidic hydrotrap to study the effect of straining flow on waterborne microorganisms
Farzan Akbaridoust
University of Melbourne
3.30pm Friday 30 June 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
We present a systematic study on the effect of straining flow on the harmful
filamentous cyanobacterium Anabaena circinalis using a cross-slot
type microfluidic device equipped with an advanced image-based real-time
control system and simultaneously quantified by micron-resolution particle
image velocimetry (micro-PIV). This enables us to monitor potential
morphological damage to, and simultaneously compute the forces on, filaments
in real-time while the filaments of the cyanobacterium are exposed to high
strain rates.
Interaction of synthetic jets with turbulent boundary layers
Tim Berk
University of Southampton
3.30pm Friday 23 June 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Synthetic jets are zero-net-mass-flux actuators that can be used in a range
of flow control applications. For several pulsed/synthetic jet in cross-flow
applications, two physical phenomena are important: 1) The variation of the
jet trajectory in the mean flow with jet and boundary layer parameters,
which will provide an indication of the penetration depth of the
pulsed/synthetic jet in to a boundary layer and 2) the losses associated
with this penetration and the various physical mechanisms that are
responsible for it. In this talk, I will present results that discuss both
the variation of trajectories with different jet and boundary layer
parameters and the mechanisms that are responsible for the losses.
The first part will focus on the mechanisms that are responsible for
momentum losses created by the interaction of a synthetic jet with a
turbulent boundary layer. Previous studies have ascribed the momentum
deficit caused by the jet to a combination of viscous blockage of the
crossflow and the upwash of low-momentum fluid. However, these contributions
have not been quantified systematically. In order to resolve these
contributions, detailed Particle Image Velocimetry measurements were carried
out to examine the interaction between a synthetic jet and a
low-Reynolds-number turbulent boundary layer at the University of
Southampton. Based on an analysis of the vortical structures identified in
the PIV data, the momentum deficit is attributed to the streamwise velocity
induced by these vortical structures. Using Biot-Savart calculations, this
induced velocity can be determined from the vorticity field obtained from
PIV. The resulting momentum deficit is shown to account for 90% of the total
momentum deficit, indicating that the advection of vortices is the main
source of momentum deficit in these flows.
In the second part of the talk I will present results that compare the mean
flow trajectories of the jet at low Reynolds number to the data obtained in
the High Reynolds Number Boundary Layer Wind Tunnel at Melbourne.
Trajectories of the synthetic jet in the turbulent boundary layer are
measured for a range of actuation parameters in both low and high Reynolds
numbers. The important parameters influencing the trajectory are determined
from these comparisons. The Reynolds number of the boundary layer is shown
to only have a small effect on the trajectory. In fact, the critical
parameters are found to be the Strouhal number of the jet based on jet
dimensions as well as the velocity ratio of the jet (defined as a ratio
between mean jet blowing velocity and the freestream velocity). An
expression for the trajectory of the synthetic (or pulsed) jet is derived
from the data, which (in the limit) is consistent with known expressions for
the trajectory of a steady jet in a cross-flow.
Tim received his BSc in Advanced Technology (2011), MSc in Mechanical
Engineering (2014) and MSc in Sustainable Energy Technology (2014) from the
University of Twente in the Netherlands. He is currently a PhD student at
the University of Southampton under supervision of Bharath
Ganapathisubramani, hoping to finish his PhD at the end of this year. For
the past two months Tim has visited the University of Melbourne, performing
experiments in the High Reynolds Number Boundary Layer Wind Tunnel.
Turbulent mixing and entrainment in density stratified riverine flows
Michael Kirkpatrick
University of Sydney
3.30pm Friday 16 June 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Maintaining the health of our river systems requires management of a limited
resource, and involves balancing the water needs of agriculture, fisheries,
urban water supplies, power generators, industry, tourism, recreational
users and the environment. As a result, many rivers are now highly regulated
and have a large proportion of their water withdrawn for human uses, leading
to flow rates significantly below their natural levels. Lowering of flow
rates can lead to serious water quality issues due to the combined effects
of longer residence times, decreased turbulent mixing and increased levels
of stabilizing density stratification due to solar heating and/or salinity.
The resulting stagnant conditions are characterized by low levels of
dissolved oxygen and the accumulation of contaminants and nutrients, which
can lead to long-term, systemic damage to riverine ecosystems. Thermal
stratification combined with low turbulence, and high radiation and nutrient
loads are also conducive to the proliferation and accumulation of toxic
cyanobacteria (blue-green algae) and other micro-organisms. Persistence of
these conditions for more than a few days has been identified as a key risk
factor for cyanobacterial outbreaks.
In this talk I will give an overview of our research on turbulent mixing and
entrainment in density stratified riverine flows. The first half of the talk
will focus on experimental and numerical studies of entrainment and mixing
processes in saline pools that form commonly in river bed depressions. The
second half of the talk will focus on recent Direct Numerical Simulation
studies of thermal stratification in turbulent open channel flow due to
radiative solar heating. I will present our recently published findings
(J. Fluid Mech., 2015) regarding the equilibrium states reached by turbulent
open channel flow with solar heating. I will then discuss our current work
in which we are investigating the primary physical processes that break down
these stratified equilibrium states, namely nocturnal surface cooling, wind
shear and river bends.
The aim of our research is to develop scaling relations that can be used in
combination with other data, such as weather forecasts, to predict the
likely occurrence of persistent stratification events. These improved
modelling capabilities will enable river managers to initiate short
time-scale tactical responses such as an environmental flow release from
upstream reservoirs in response to drought or heat-wave conditions in order
to maintain water quality and river health. It will also enable them to
better optimize long-term water management strategies such as the
distribution of water allocations amongst stakeholders, taking into account
predicted changes in land-use patterns and climate.
Michael Kirkpatrick graduated with a degree in Mechanical Engineering from
the University of Sydney in 1996. He then worked with the international
building engineering consultancy Ove Arup & Partners in Sydney and their
London office. Michael returned to Australia in 1998 to study for a PhD at
the University of Sydney. On completion of his PhD in 2002, he was awarded
a two year Postdoctoral Fellowship with the Center for Turbulence Research
at Stanford University and NASA Ames. In 2004 he accepted a lecturing
position in the School of Engineering at the University of Tasmania. In 2006
Michael returned to the University of Sydney where he is currently an
Associate Professor in Fluids, Energy and Environment in the School of
Aerospace, Mechanical and Mechatronic Engineering.
Generation of a classical vortex ring and its axial interaction with a cylinder
Debopam Das
Department of Aerospace Engineering, Indian Institute of Technology Kanpur
3.30pm Wednesday 14 June 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
In this talk I will discuss a novel method for generating vortex rings
that circumvents some of the drawbacks associated with existing methods.
The predominant effects that occur in previously used methods are due to
the presence of some of the other vortices such as, stopping
vortex, piston vortex, image vortex and orifice lip generated vortices in
the early stage of development. These disturbances influence the geometric,
kinematic and dynamic characteristics of a vortex ring and lead to
mismatches with classical theoretical predictions. It is shown in the
present study that the disturbance free vortex rings produced follow the
classical theory. Flow visualization and PIV experiments are carried out in
the Reynolds number (defined as ratio of circulation Γ and
kinematic viscosity ν) range, 2270 < ReΓ < 6790,
to find the translational velocity, total and core circulation, core
diameter, ring diameter and bubble diameter. In reference to the earlier
studies, significant differences are noted in the variations of the vortex
ring diameter and core diameter. A model for core diameter during formation
stage is proposed. The translational velocity variation with time shows that
the second-order accurate formula derived using Hamilton's equation by
Fraenkel (J. Fluid Mech., 1972, vol. 51, pp. 119–135) predicts it
best.
Subsequently the axial interaction of this classical vortex ring with a
thin circular cylinder has been studied. It is observed that due to the
presence of the cylinder, there is an increase in the velocity of the vortex
ring. Also, noticeable changes in the characteristic properties of vortex
ring such as core circulation, core diameter and ring diameter have been
observed. To justify these experimental observations quantitatively, an
analytical study of the interaction under inviscid assumption is performed.
The inviscid analysis does predict the increase in velocity during the
interaction, but fails to predict the values observed in experiments.
However, when the theory is used to correct the velocity change through
incorporation of the effects of axisymmetric induced boundary layer region
over the cylinder, modelled as an annular vortex sheet of varying strength,
the changes in the translational velocities of vortex rings match closely
with the experimental values.
Dr. Debopam Das is a professor of the Department of Aerospace Engineering,
IIT Kanpur, India. He obtained PhD degree from Indian Institute of Science
Bangalore. He has worked as Senior Research Scientist, Temasek Laboratory at
National University of Singapore, Postdoctoral Research fellow in Florida
State University and as an Assistant Professor, in the Department of
Mechanical Engineering, IIT, Guwahati, India. His research interest is in
flapping flight, incompressible and compressible vortex rings, instabilityo
and transition of unsteady internal flows and instability of buoyant and
non-buoyant free shear flows. He received Excellence in Aerospace Education
award for 2015 by Aeronautical Society of India.
Flow generated by surface waves
Horst Punzmann
Research School of Physics and Engineering, Australian National University
3.30pm Friday 9 June 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Trajectories of fluid parcels on the surface have been described
analytically for progressing irrotational waves, where particles move in the
direction of wave propagation. Waves in the laboratory and in nature are
more complex due to the development of instabilities that render ideal
planar 2D propagating waves into complex 3D waves. In this talk I will
present experiments in the short wavelength gravity-capillary range that
demonstrate different surface flow phenomena. Propagating waves, driven by
a vertically oscillating plunger, can lead to a flow reversal when wave
instabilities render planer wave fronts into wave packets at high amplitude.
At small-amplitude, stable flow pattern can be achieved in stationary
(rotating) two-dimensional wave fields that are produced by
phase-synchronised wave paddles. The role of surface vorticity generation
by waves will be discussed.
Dr Horst Punzmann is research engineer at the Research School of Physics and
Engineering at the Australian National University (ANU), Canberra. He
obtained his undergraduate degree in Electrical Engineering at the
University of Applied Science in Regensburg, Germany and worked in analog
integrated circuit design in the automotive industry for 5 years. After
this, he did his PhD in high-temperature plasma physics at the ANU and
studied plasma turbulence and particle transport while being facilities
manager of the Australian Plasma Fusion Research Facility for 10 years. He
switched to hydrodynamic turbulence a while ago and his current research
interest in the Physics of Fluids group is related to the interaction of
surface waves and flows.
Confirmation: Air-sea interaction: laboratory study on the air-side turbulence of wind-wave
Tunggul Bhirawa
University of Melbourne
4pm Friday 2 June 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Wind is the main driving force in ocean wave generation, however the process
of energy transfer from wind to wave is poorly understood. In order to
explain the process comprehensively, we need to study how the atmosphere
(air) and sea interacts. Air-sea interaction is relevant to understanding
the coupled atmosphere-ocean system. The interactions involve small- and
large-scale transfers of momentum, heat and mass, which affect our weather
and climate. The knowledge of air-sea interaction is essential for
industries related to the ocean system (ports and harbors, shipping, oil
and gas offshore platforms) and for the ocean research community as
well.
The common problem in studying this subject is to measure important
quantities (sea drag, roughness length) close to the ocean surface which
brings engineering and logistical challenges. In extreme conditions, such as
in tropical cyclones, the uncertainty is higher since predictions are often
extrapolated from lower wind speeds. This is where laboratory study is
needed to make measurements possible.
PIV measurements were conducted to investigate the air-side turbulence above
wind generated waves at the Extreme Air-Sea Interaction (EASI) facility in
the Michell Hydrodynamics Laboratory. The objective is to study the
behaviour of sea drag coefficient and roughness length under different wind
speed and sea state conditions, which have been the most sought-after
measurements in the study of air-sea interaction (Donelan et al.
1993).
Dynamic behaviours of composite panel subjected to underwater blast: fluid-structure interaction (FSI) experiment and numerical simulation
Jonathan Tran
Department of Infrastructure Engineering, University of Melbourne
4pm Friday 26 May 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Designing lightweight high-performance materials that can sustain underwater
impulsive loadings is of great interest for marine applications. In this
study, underwater experiments are conducted and validated with a novel
finite element fluid-structure interaction to understand the deformation and
failure mechanisms of both monolithic and E-glass/Vinylester/H250 PVC
sandwich composite panels. The experimental setup simulates fluid-structure
interactions (FSI) encountered in various applications of interest. To
generate impulsive loading similar to blast, a specially designed flyer
plate impact experiment was designed and implemented. The design is based on
scaling analysis to achieve a laboratory scale apparatus that can capture
essential features in the deformation and failure of large scale naval
structures. In the FSI setup, a water chamber made of a steel tube is
incorporated into a gas gun apparatus. A scaled structure is fixed at one
end of the steel tube and a water piston seals the other end. A flyer plate
impacts the water piston and produces an exponentially decaying pressure
history in lieu of explosive detonation. The pressure induced by the flyer
plate propagates and imposes an impulse to the structure (panel specimen),
which response elicits bubble formation and water cavitation. Failure modes,
damage mechanisms and their distributions are identified and quantified for
composite monolithic and sandwich panels subjected to typical blast
loadings. The temporal evolutions of panel deflection and centre deflection
histories were obtained from shadow Moiré fringes acquired in real
time by means of high speed photography.
Dr Jonathan (Phuong) Tran received his PhD degree in Theoretical and Applied
Mechanics at the University of Illinois, Urbana Champaign (UIUC, USA, 2010)
on the development of Laser-induced compressive shockwave technique to
investigate the dynamic delamination of multilayer thin film structures.
Following his PhD, Dr Tran has been working as a postdoctoral researcher in
Mechanical Engineering department at the Northwestern University (Evanston,
IL, USA) on an ONR-funded project to investigate the performance of
composite material subjected to underwater blast loading. His current
position is a lecturer in the department of Infrastructure Engineering, the
University of Melbourne. He has been involved and contributed to number of
successful ARC Linkage and Discovery projects, CRC-Project and other
defence-related grants from Defence Materials Technology Centre (DMTC) and
CSIRO Manufacturing Flagship. His research interests include dynamic
behaviours of composite structure under extreme loadings (air/underwater
blast, ballistics impacts, wind and fire) and design optimisation of
bio-mimicry and lightweight composite materials. He has published 50
journal papers and a book chapter on related topics.
Natural convection in the near shore regions of lakes and reservoirs induced by the absorption of solar radiation
John Patterson
School of Civil Engineering, University of Sydney
4pm Friday 19 May 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
In the near shore region of lakes and reservoirs where the depth decreases
towards the shore, the incidence of solar radiation results in a complex
motion which provides a mechanism for natural convection heat and mass
transfer between the shore and the main water body. This has potentially
significant consequences for water quality issues and therefore management
of the resource. The flow also has wider implications for any contained
fluid heated by radiation. The mechanism operates as follows. Incident
radiation is absorbed by the water column in an exponentially decaying
manner. The absorption of the radiation in this fashion gives rise to a
stable temperature stratification in the upper regions of the water column.
However, in the shallower parts, some radiation reaches the bed, and is
re-emitted as a heat flux. There are two consequences of this: first, the
volumetric rate of heating is greater in the shallow part than in the deep,
which gives rise to a horizontal temperature gradient and therefore to a
circulation up the slope and outward at the surface from the shore line; and
second, the emission of heat from the bed gives rise to a potentially
unstable temperature gradient at the bed which may cause intermittent rising
plumes. In this presentation I discuss the development of the understanding
of the key characteristics of this complex flow, including recent numerical,
scaling analysis and experimental investigations. In particular I report
some recent laboratory experiments using concurrent PIV and shadowgraph for
measurement and visualisation which demonstrate both the underlying
circulation and the presence of the rising plumes. The characteristics of
these flows are compared with earlier scaling analysis results, and the
underlying mechanism descriptions verified. Finally, linear stability
analysis provides some of the characteristics of the rising plumes.
John received his PhD in Applied Mechanics from the University of
Queensland. He moved to University of Western Australia as postdoctoral
fellow, took up an academic post in the Department Civil Engineering,
and eventually became Head of the School of Environmental Engineering. He
moved to James Cook University in Townsville in 1997, and became the
founding head of the merged School of Engineering. In 2009 he joined
the School of Civil Engineering at the University of Sydney as Professor
of Fluid Mechanics and Director of the Wind Waves and Water Centre. From
2011–2015 he was Associate Dean Research for the Faculty of
Engineering and IT at the University of Sydney.
John has served on a number of journal editorial boards, and has been a
member of ARC assessment panels, including what is now called the College
of Experts, Centre of Excellence selection panels, and the ERA Evaluation
Committee. He has held visiting research appointments in Canada, Germany,
UK, and the USA. He has published over 200 articles in the international
literature. He has generated in excess of $7M in ARC Discovery or equivalent
research grants.
John's research interests are historically in mixing and transport in
lakes and reservoirs and the implications for water quality, and more
recently, in natural convection flows, with environmental and industrial
applications. His research encompasses theoretical, experimental and
numerical investigations.
Adjoint-based optimal flow control and invariant solutions in compressible 2D cavity flows
Javier Otero
University of Melbourne
4pm Friday 12 May 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The advances in the understanding of compressible flows challenge
researchers to tackle more ambitious problems that surpass human intuition.
Hence, it becomes necessary to rely on methods that give an insight into the
underlying physical mechanisms that govern these complex flows to perform
non-trivial tasks such as flow control. To this end, an adjoint-based
optimal flow control framework for compressible flows has been appended to
an existing in-house DNS code (HiPSTAR). In particular, we focus our efforts
on a 2D cavity flow at Re=5000, where we aim to reduce noise levels at the
sensor location, by either reducing the overall sound radiation or altering
the sound directivity. In addition, with minor coding effort, this framework
is extended to permit the computation of both (stable and unstable) exact
steady and periodic flow solutions in compressible flows over complex
geometries. Thus, we present the families of exact periodic and steady
solutions across Mach number, using the same 2D cavity flow setup with a
lower Reynolds number (Re=2000). These two families of flow solutions are
found to meet at the quasi-incompressible flow regime, where a stability
analysis on both periodic and equilibrium solutions shows that they form a
subcritical Hopf bifurcation
Javier did his undergraduate in Aerospace Engineering at the Technical
University of Madrid (UPM), Spain (2008–2012); an MSc in
Computational Fluid Dynamics at Cranfield University, UK (2012–2013);
and PhD in development and application of an adjoint-based optimal flow
control framework for compressible DNS at Southampton University, UK
(2013–2017). He is now a postdoc working with Prof Richard Sandberg.
Shock driven instabilities in two-fluid plasmas
Vincent Wheatley
University of Queensland
4pm Friday 28 April 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
In inertial confinement fusion (ICF) experiments, a capsule filled with fuel
is imploded by shock waves generated by laser-driven ablation. The goal is
to ignite a fusion burn at the centre of the implosion, and have that burn
propagate through and consume the inertially confined fuel. Hydrodynamic
instabilities cause mixing between the capsule material and the fuel, which
is highly detrimental to the propagation of a fusion burn. One of the key
hydrodynamic instabilities in ICF is the Richtmyer-Meshkov instability
(RMI). This occurs when a shock interacts with a perturbed density
interface, such as the interface between the capsule and the fuel. In ICF
and astrophysical applications, the RMI typically occurs in plasmas. Here,
we study the RMI in the context of the ideal two-fluid, ion-electron,
continuum equations. These couple a separate set of conservation equations
for each species to the full Maxwell equations for the evolution of the
electromagnetic fields. We focus on cases with and without an imposed
magnetic fields and with Debye lengths ranging from a thousandth to a tenth
of the interface perturbation wavelength. For all cases investigated, the
behaviour of the flow is substantially different from that predicted by the
Euler or ideal magnetohydrodynamics equations. Electric fields generated by
charge separation cause interface oscillations, particularly in the
electrons, that drive a secondary high-wavenumber instability. Consequently,
the density interface is substantially more unstable than predicted by the
Euler equations for all cases investigated. Self-generated magnetic fields
are predicted within our simulations, but their orientation is such that
they do not dampen the RMI. In ideal magnetohydrodynamics (MHD), it has been
shown that in the presence of such a seed magnetic field, the growth of the
RMI is suppressed by the transport of vorticity from the interface by MHD
shocks. Our two-fluid plasma simulations reveal that while the RMI is
suppressed in the presence of the seed field, the suppression mechanism
varies depending on the plasma length-scales. Two-fluid plasma RMI
simulations also reveal that the secondary, high-wavenumber, electron-driven
interface instability is not suppressed by the presence of the seed
field.
Dr Vincent Wheatley is a senior lecturer in the Centre for Hypersonics
within the School of Mechanical and Mining Engineering at the University of
Queensland. He obtained his PhD in Aeronautics from the California
Institute of Technology in 2005. He also earned an MEngSc (Mechanical) and a
BE (Mechanical and Space) from the University of Queensland (UQ). After
completing his PhD in the US, Dr Wheatley spent two years as post-doctoral
fellow at ETH Zurich. He was then a Lecturer in Aerospace Engineering at the
University of Adelaide before taking up his position at UQ in 2009.
Non-laminar solutions for grooved Couette flow
Sabarish Vadarevu
University of Melbourne
4pm Friday 21 April 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The dynamical systems approach to turbulence has gained a lot of attention
since the turn of the century. A large set of exact, symmetrical solutions
of the Navier-Stokes equations have been found for canonical wall-bounded
flows such as Couette, channel, and pipe flows at low Reynolds numbers
(~ 400). The defining characteristic of these solutions is the vortex-streak
structure that is known to play a crucial role in sustaining near-wall
turbulence. In state-space, some of these solutions lie in the region that
is densely visited by turbulence, while some others resemble the laminar
solution and regulate laminar-turbulent transition. These solutions, along
with their connections in state-space, form a skeleton for trajectories of
turbulent flow. In addition to providing a description of turbulence
dynamics, this approach also produces an equation-based, low-rank basis for
use in flow control.
This vision of turbulence has not been extended to rough-walled flows
despite their practical significance. We have taken the first steps in this
direction by computing exact invariant solutions for plane Couette flow with
(longitudinal) grooved walls, through continuation of known solutions for
smooth-walled flows using a simple domain transformation method. We find
that the principal role of such grooves is to localize the vortex-streak
structure near the wall, as well as to reduce the bulk energy density while
increasing the dissipation rate. Similar localization of the structure is
considered to produce drag reduction (~ 10%) in riblet-mounted boundary
layers. While these results are fairly primitive, especially due to the low
Reynolds numbers involved, we believe that further efforts in this direction
can help in optimizing riblet geometries for drag reduction, and provide
insight on the influence of surface-roughness on the near-wall flow.
Sabarish Vadarevu is a research fellow in the fluids group at the University
of Melbourne. He worked on his PhD (awaiting completion) in Aerospace
Engineering at the University of Southampton, on computing exact invariant
solutions in grooved plane shear flows. Prior to that, he obtained his
Bachelors and Masters degrees from the Indian Institute of
Technology-Madras, with his Masters thesis involving a stability analysis
of partially premixed flames in laminar mixing layers. His current research
is focused on linear modelling and control of wall-bounded turbulence.
LES for loss prediction in an axial compressor cascade at off-design incidences
Jake Leggett
University of Southampton
4pm Tuesday 11 April 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The work focuses on the prediction of loss in axial compressors. The
majority of modern design methods use cheaper more accessible models, such
as RANS, to predict flow performance. While these methods are reliable and
easier to use they do not always provide the accuracy needed. The aim of the
work presented is to improve our understanding of how models like RANS
behave under more challenging conditions. Using higher fidelity LES
simulations it is possible to assess the performance of RANS under such
conditions and aid designers by highlighting short comings and improving the
application of such tools.
Jake Leggett is a PhD candidate at the University of Southampton, studying
loss prediction in axial compressors. Having previously done a bachelors in
mechanical engineering followed by an MSc in CFD at Imperial College London.
His interests are in compressible fluid dynamics and numerical methods,
focussing on modelling behavior and the performance of numerical models in
capturing physically realistic flows.
Confirmation: Numerical investigations of hemodynamic changes in stented coronary arteries
Bo Jiang
University of Melbourne
9am Wednesday 5 April 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Incomplete stent apposition (ISA) is sometimes found in stent deployment at
complex lesions, and it is considered to be one of the causes of
post-stenting complications, such as late stent thrombosis and restenosis.
The presence of ISA leads to large recirculation bubbles behind the stent
struts, which can reduce shear stress at the arterial wall that retards
neointimal formation process and thus lead to complications. Computational
fluid dynamics (CFD) simulations are performed on simplified two-dimensional
axisymmetric arterial models with stents struts of square and circular
cross-sectional shapes at a malapposition distance of 120 μm from the
arterial wall. Under the condition of the same flow rate, both square and
circular strut cases show that shorter period provides greater flow
deceleration, leading to the formation of a larger recirculation bubble.
With the same thickness, circular strut has a significant improvement over
the square strut in terms of the size of the recirculation bubble, and
therefore less likely to lead to complications. We also carried out
three-dimensional computational fluid dynamics studies on a partially
embedded coronary stent. Stent struts are partially embedded in portion of
the circular and elliptical artery's circumference and malaposed elsewhere.
Maximum malapposition distances (MD) used in this study are 0.255 mm
(moderate) and 0.555 mm (severe). Time-averaged wall shear stress (TAWSS) is
used as the haemodynamic metric to evaluate the clinical significance of
ISA. TAWSS decreases along the circumferential direction as MD decreases
from the maximum ISA side to the embedded side. The case with severe ISA
has a larger area of high TAWSS on the arterial wall at the proximal end and
low TAWSS at the distal end of the stent.
Theoretical framework for the upscaling of physical interactions in aquatic mobile-boundary flows
Konstantinos Papadopoulos
University of Melbourne, University of Aberdeen
4pm Tuesday 28 March 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Most environmental flows often exhibit high levels of spatial and temporal
heterogeneity in hydrodynamic fields due to the effects of multi-scale
roughness elements and their mobility. These effects are especially profound
in the near-bed region. The development of a unifying framework for the
integration and upscaling of the fluid mechanical, ecological and
biomechanical processes occurring in such conditions is needed. Particular
focus in this study is on the interactions of the fluid motion with the
motions of aquatic plants and sediments in aquatic systems.
To cope with the temporal and spatial heterogeneity of the flow field near
the flow interface with a second non-fluid phase, the governing equations of
motion are averaged over time and space. To deal with the possible
discontinuity of the averaged fields within the averaging domains,
appropriate definitions and theorems for time and space averaging are
used.
Appropriately formulated coupled double-averaged conservation equations are
developed for fluid, sediment, and plant motions. Complementary equations
for the second-order velocity moments introduced by the averaging process
are also proposed. Due to the double-averaging methodology (i) the governing
equations are up-scaled to the scales relevant to applications, (ii) the
fluid motion is rigorously coupled with the non-fluid (plants or sediments)
motions, and (iii) the effect of the moving interfacial boundary is
introduced explicitly in the governing averaged equations.
This presentation introduces to the main concepts and key steps involved in
the derivation of the double-averaged equations outlined above, discusses
their application to the analysis of high-resolution data sets and
identifies potential applications in mobile-boundary flow studies.
Konstantinos performed his PhD research on flow-biota and flow-sediment
interactions in rivers and open-channel flows at the University of Aberdeen,
where he was on a Marie-Curie Fellowship. Prior to that, he obtained
an MSc in coastal engineering at the National Technical University of
Athens (2013) and MEng in environmental engineering at the Technical
University of Crete (2009).
High resolution simulation of dissolving ice-shelves in sea water
Bishakhdatta Gayen
Research School of Earth Sciences, Australian National University
4pm Friday 24 March 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Precise knowledge of ocean dynamics and interactions with the grounded ice
at high latitudes is very crucial for predicting the sea-level rise and
further development of adaptation strategies in a warming global climate.
The physics of these ocean–ice interactions particularly related to
small scale processes, is poorly understood which, along with limited
observation constraints, leads to uncertainties in the predictions of future
melt rate. We perform high resolution numerical simulation to investigate
dissolving of ice into cold and salty sea water. The three coupled interface
equations are used, along with the Boussinesq and non-hydrostatic governing
equations of motion and equation of state for seawater, to solve for
interface temperature, salinity, and melt rate. The main focus is on the
rate of dissolving of ice at ambient water temperatures between
−1°C and 2°C and salinity around 35 psu and the dependence on
stratification (as characterizes many sites around Antarctica). Our
simulation also shows boundary layer next to the ice face is dominated by
turbulent motions. It is also important to quantify the difference between
the melting of a vertical ice wall and the melting of a sloping ice shelf.
The basal slope is observed to vary significantly, due to the formation of
crevasses, channels and terraces. Our high-resolution simulations are
designed for direct comparison with laboratory measurements and theory. The
temperature and density structures found under Pine Island Glacier show
several layers having a vertical scale that can also be explained by this
study.
Bishakhdatta Gayen received a degree in Bachelor of Mechanical Engineering
from Jadavpur University in Kolkata, India in 2006, and a M.S. degree in
Engineering Science, majoring in Fluid Mechanics, from the Jawaharlal Nehru
Centre for Advanced Scientific Research, Bangalore, in 2007. He was then
awarded a University of California Graduate Fellowship and received an M.S.
(2010) and Ph.D. (2012) from University of California, San Diego. He pursued
research work on "Turbulence and Internal Waves in Tidal Flow over
Topography" under the guidance of Prof. Sutanu Sarkar and was awarded the
Andreas Acrivos Award for Outstanding Dissertation in Fluid Dynamics from
the American Physical Society. He moved to Australia to pursue his
postdoctoral research with Prof. Ross W. Griffiths at the Australian
National University in Canberra. Bishakh is currently an Australian
Research Council Discovery Early Career Fellow. His current research
interests are nonlinear internal waves in the ocean, turbulent convection,
modeling of Antarctic ice melting and Southern ocean dynamics.
The vortices of V. Strouhal
David Lo Jacono
Institut de Mécanique des Fluides de Toulouse
4pm Friday 17 March 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
During this seminar, I will talk about the link between Strouhal's findings
and vortices. We learn that the Strouhal number characterises the shedding
frequency of vortices behind a bluff-body, yet Strouhal never encountered a
vortex. I will try to show the role played by various well-known researchers
(Rayleigh, Bénard, Kármán, etc.), and others that are
less well known yet have a key role towards understanding wake dynamics.
Starting from the motivation of Strouhal and ending with the modern analysis
of wakes in 1930, I will try to build an incomplete and brief history of
19th-20th century (wake) fluid mechanics focussing on motivation and
experimental insights. This work was originally part of my ScD dissertation
and further completed for the recently held colloquium "A century of Fluid
Mechanics 1870-1970" celebrating the IMFT century anniversary.
Skin-friction and vorticity fields in wall-bounded flows and the attached eddy hypothesis
Min Chong
University of Melbourne
4pm Friday 10 March 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The invariants of the velocity gradient tensor have been used to study
turbulent flow structures in order to extract information regarding the
scales, kinematics and dynamics of these structures. These invariants cannot
be used to study structures at a no-slip wall since they are all zero at the
wall. However, the flow structures at the wall can be studied in terms of
the invariants of the "no-slip tensor". Employing surface flow patterns
generated using local solutions of the Navier-Stokes equations, the
relationship between the surface skin-friction field and vorticity field
will be explored. These local solutions, together with data from the Direct
Numerical Simulations of channel flows, pipe flows and boundary layer flows
may perhaps lead to a better model for the structure of attached eddies in
wall bounded flows.
Linear estimation of large-scale structures in channel flow at Reτ = 1000
Simon Illingworth
University of Melbourne
4pm Friday 3 March 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Given the time-resolved velocity field in a plane at a single wall-normal
height, how well can one estimate, using a linear model alone, the
time-resolved velocity field at other wall-normal heights? This question
will be explored for channel flow at Reτ = 1000 using data
from the John Hopkins Turbulence database. Two different linear models will
be explored. Each linear model has its origins in the Navier–Stokes
equations.
Subfilter-scale stress modelling for large-eddy simulations
Amirreza Rouhi
University of Melbourne
4pm Friday 24 February 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
A subfilter-scale (SFS) stress model is developed for large-eddy simulations
(LES) and is tested on various benchmark problems in both wall-resolved and
wall-modelled LES. The basic ingredients of the proposed model are the model
length-scale, and the model parameter. The model length-scale is defined as
a fraction of the integral scale of the flow, decoupled from the grid. The
portion of the resolved scales (LES resolution) appears as a user-defined
model parameter, an advantage that the user decides the LES
resolution.
The model parameter is determined based on a measure of LES resolution, the
SFS activity. The user decides a value for the SFS activity (based on the
affordable computational budget and expected accuracy), and the model
parameter is calculated dynamically. Depending on how the SFS activity is
enforced, two SFS models are proposed. In one approach the user assigns the
global (volume averaged) contribution of SFS to the transport (global
model), while in the second model (local model), SFS activity is decided
locally (locally averaged). The models are tested on isotropic turbulence,
channel flow, backward-facing step and separating boundary layer.
In wall-resolved LES, both global and local models perform quite accurately.
Due to their near-wall behaviour, they result in accurate prediction of the
flow on coarse grids. The backward-facing step also highlights the advantage
of decoupling the model length-scale from the mesh. Despite the sharply
refined grid near the step, the proposed SFS models yield a smooth, while
physically consistent filter-width distribution, which minimizes errors when
grid discontinuity is present.
Finally the model application is extended to wall-modelled LES and is tested
on channel flow and separating boundary layer. Given the coarse resolution
used in wall-modelled LES, near the wall most of the eddies become SFS and
SFS activity is required to be locally increased. The results are in very
good agreement with the data for the channel. Errors in the prediction of
separation and reattachment are observed in the separated flow, that are
somewhat improved with some modifications to the wall-layer
model.
Amirreza Rouhi is a postdoctoral fellow in the fluids group at the
university of Melbourne. Amirreza received his PhD in Mechanical Engineering
from Queen's University of Canada under supervision of Prof. Piomelli, doing
subfilter-scale (SFS) stress modelling as his PhD thesis. His other research
interests include wall-modelled LES, spectral methods and rotating
turbulence.
Completion: The minimal-span channel for rough-wall turbulent flows
Michael MacDonald
University of Melbourne
4pm Friday 10 February 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Turbulent flows over roughness are ubiquitous in engineering and geophysical
applications, however their effects are primarily given through
semi-empirical models and approximations. The accuracy of these methods is
sensitive to the model and roughness topology in question, so that
laboratory experiments and conventional direct numerical simulations (DNS)
remain the desired standard in rough-wall studies. However, these techniques
are expensive for both industry and researchers, making design predictions
and the examination of rough-wall flows challenging. In this talk, we
outline a framework termed the minimal-span channel in which fully resolved
numerical simulations of rough-wall flows can be conducted at a reduced cost
compared to conventional DNS. The minimal-span channel is used to simulate
turbulent flow over a variety of roughness geometries that would otherwise
be prohibitively expensive to study. Special attention is given to recent
simulations of rectangular bars aligned in the spanwise direction, commonly
called d-type roughness.
Completion: Reorganising turbulence using directional surface patterns
Kevin
University of Melbourne
4pm Wednesday 1 February 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
We attempt to passively reorganise wall turbulence using
transitionally-rough surface patterns in the form of herring-bone riblets.
The flow fields are investigated experimentally using large field-of-view
particle image velocimetry in all orthogonal planes. The pronounced
modification of the boundary layer suggests that a preferential arrangement
of the naturally-occurring turbulence events may have been introduced. The
spatial information captured in these multiple orientations enable us to
clearly observe distinct turbulence events, such as the unstable outer
layer, non-symmetrical vortical motions and strong streamwise-periodic
events. Interestingly, our recent analysis indicates that the aforementioned
events we thought was induced by the surface pattern, though weaker, are
actually present in the smooth-wall (canonical) flows. In the average
picture however, these structural attributes are masked by their random
occurrences in space. This further suggests that we can passively reposition
and perhaps manipulate large turbulence structures.
DNS study on relation between vorticity and vortex
Chaoqun Liu
University of Texas at Arlington, Texas, USA
2pm Monday 23 January 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Vorticity, vorticity line, vorticity tube have rigorous mathematical
definition, but the rigorous definition of vortex is still an open
question. However, for long time until now, in many research papers
and text books, vortex is defined as vorticity tube confined by
vorticity lines without vorticity line leakage. Vortex is also
considered as congregation of vorticity lines with larger vorticity.
Our DNS study shows that vortex is not a vortex tube but open for
vorticity line penetration, is not a congregation of vorticity lines
but a dispersion of vorticity lines, is not a concentration of
vorticity with larger vorticity but with smaller vorticity in most
3-D cases. In general, vortex is an intuitive concept of rotation
core with weak dissipation, e.g. zero dissipation when it becomes
rigid rotation. In addition, vortex is not a vorticity tube, being
different from what suggested by many research papers and textbooks.
At the laminar boundary layer, vorticity is large but we have no
vortex. A core with 2 nearly pure rotations per second, where
vorticity is small, is a vortex, but a core with 10000 strongly
sheared rotation, where vorticity is very large but deformation is
very large as well, may not be a vortex. Therefore, vorticity
magnitude and vortex are irrelevant. Unlike solid body, vortex is
always a mixture of vorticity and deformation and vortex is really
defined as an open area (not tube) where deformation is weak and
vorticity is dominant. A function so-called "Omega" is defined to
identify the vortex and Omega=0.52 well represents the vortex area
boundary. Vortex is mathematically defined as Omega >0.5 which
means a place where vorticity overtakes deformation. The minimum
gradient of "Omega" is well representing the vortex axis. Several
examples including DNS for late flow transition and LES for shock
vortex interaction have been tested and the outcome is
promising.
Chaoqun Liu is a Distinguished Professor and CNSM Center Director
in the Department of Mathematics, University of Texas at Arlington,
Arlington, Texas, USA.
Completion: The structure and scaling of rough-wall turbulent boundary layers
Dougal Squire
University of Melbourne
2pm Wednesday 21 December 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Turbulent wall layers are a pervasive and influential feature in nature and
engineering; common examples include the atmospheric and benthic layer
(relevant to weather prediction and pollutant dispersion, for example),
boundary layers developing on aerial, marine and terrestrial vehicles (such
as aeroplanes, naval vessels, cars and trains), and flows in piping
networks. These flows are characterised by high Reynolds numbers and, more
often than not, surface roughness that exerts a dynamical effect on the
flow. The latter may result from manufacturing defects, erosion and/or
deposition, including that of living organisms. In this talk, we will
present results from recent measurements of rough-wall turbulent boundary
layers spanning a very wide range of friction and roughness Reynolds
numbers. The results comprise 38 datasets and four experimental techniques,
including hot-wire anemometry and particle image velocimetry. Our analysis
will focus broadly on the relationship between the outer region flow and
near-wall structures which are directly influenced by the roughness
scale(s). Features of this relationship will be discussed using
single-point statistics, measures of spatial structure, and the inner-outer
interaction model of Marusic et al. (Science, 2010, vol. 329,
pp. 193–196).
Confirmation: Entrainment and interface dynamics of turbulent plumes
Himanshu Mishra
University of Melbourne
10am Wednesday 9 November 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Turbulent plumes form when a fluid of one density is injected into
another quiescent fluid with a different density. From violent
volcanic eruptions to the smoke rising from a cigarette, turbulent
plumes are omnipresent in nature at wide range of scales. One of the
fundamental aspects in the understanding of turbulent plumes is the
process of 'entrainment', the mixing of surrounding fluid into the
plume. Unlike non-buoyant flows, plumes pose a challenge in using
common optical measurement techniques like particle image
velocimetry (PIV) and planar laser induced fluorescence (PLIF),
because of the local changes in refractive index, when two fluids
mix. This has led to most of the previous research being focused on
global measurements of entrainment, whereas the local measurements,
which are required for clearer understanding the entrainment
phenomenon are practically non-existent. One of the ways to
circumvent this problem is to match the refractive index of two
solutions while maintaining the density difference, by adding
certain chemicals to them. Alternatively, a measurement technique
named Background Oriented Schlieren (BOS), which uses the local
refractive index changes to quantify the local density variations,
can be used.
With the final aim of understanding the process of entrainment in
turbulent plumes, we present preliminary results for two
experimental studies. (i) Velocity measurements in a vertical round
axisymmetric turbulent jet in a newly constructed experimental
facility, and (ii) free settling sphere in a sharp density interface
using BOS.
Hydrodynamic forces on geometrically porous structures
Scott Draper
University of Western Australia
4pm Friday 28 October 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Prediction of hydrodynamic forces on geometrically porous
structures is important for many applied problems in offshore
engineering. However, the accurate prediction of these forces is
complicated by the fact that the bulk velocity of the flow passing
through a porous structure is a function of its porosity. In this
talk I will present a theoretical model built on control volume
arguments which may be used to estimate the bulk velocity of the
flow passing through an isolated porous structure and, in turn,
the resulting hydrodynamic force on the structure. Extensions of
the model will be introduced to consider multiple porous
structures in close proximity, inviscid shear flow and non-uniform
porosity. It will be shown how these extensions have been used in
recent work to optimise the layout of wind and tidal turbine
arrays, estimate forces on offshore space frame structures and
predict the flow through patches of aquatic vegetation.
Dr Scott Draper is a senior lecturer at the University of Western
Australia. His research focuses on offshore fluid mechanics
applied mostly to the oil and gas and renewable energy industries.
This has included research on the stability of subsea
infrastructure, the optimum arrangement of marine renewable energy
devices and the hydrodynamics of floating bodies. He is fortunate
to work with numerous industry partners including Shell, Woodside
and Carnegie Wave Energy.
Pulse-burst PIV in high-speed flows
Steven Beresh
Aerosciences Department Sandia National Laboratories
4pm Wednesday 26 October 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Time-resolved particle image velocimetry (TR-PIV) has been achieved
in a high-speed wind tunnel and a shock tube, providing velocity
field movies of compressible turbulence events. The requirements of
high-speed flows demand greater energy at faster pulse rates than
possible with the TR-PIV systems developed for low-speed flows. This
has been realized using a pulse-burst laser to obtain movies at up
to 50 kHz with higher speeds possible at the cost of spatial
resolution. The constraints imposed by use of a pulse-burst laser
are a limited burst duration of 10.2 ms and a low duty cycle for
data acquisition. Pulse-burst PIV has been demonstrated in a
supersonic jet exhausting into a transonic crossflow and in
transonic flow over a rectangular cavity. The velocity field
sequences reveal the passage of turbulent structures and can be used
to find velocity power spectra at every point in the field,
providing spatial distributions of acoustic modes and revealing
turbulence scaling laws. Additional applications in a shock tube
show the transient onset of a von Kármán vortex street
shed from a cylinder and particle drag in a shocked dense gas-solid
flow. The present work represents the first use of TR-PIV in a
high-speed ground test facility.
Steven J. Beresh is a Distinguished Member of the Technical Staff at
Sandia National Laboratories in Albuquerque, New Mexico, U.S.A.,
where he has worked since 1999 and currently leads the Experimental
Aerosciences Facility. He received his B.S. in Mechanical
Engineering from Michigan State University in 1994 and his Ph.D. in
Aerospace Engineering from The University of Texas at Austin in
1999. His research interests emphasize the use of optical
diagnostics for compressible aerodynamics, particularly particle
image velocimetry, but utilize a variety of laser-based
instrumentation techniques and high-frequency surface sensors. He
also is responsible for a wide range of wind tunnel testing and
facility operation. He is an Associate Fellow of the American
Institute for Aeronautics and Astronautics, the Chair for the AIAA
Aerodynamic Measurement Technology Technical Committee, and is a
past President of the Supersonic Tunnel Association
International.
Development effects in turbulent boundary layers: zero and adverse-pressure-gradients
Ramis Örlü
KTH Royal Institute of Technology Sweden |
Website
4pm Friday 14 October 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
In this talk, we discuss a number of different aspects pertinent to
zero pressure gradient (ZPG) turbulent boundary layers (TBLs), and
extend these to moderate and strong adverse pressure gradients
(APGs). We start out with inflow and tripping effects in ZPG TBLs
and show their persistence in the outer layer beyond Reynolds
numbers (Re) that could be reached just few years ago by means of
direct numerical simulations (DNS). When it comes to APG TBLs, the
situation has usually been more blurry when considering literature
data, due to their dependency on the pressure-gradient strength and
streamwise history, besides Reynolds number effects. Based on
different APG TBLs developing on flat plates and the suction side of
a wing, we aim at distinguishing the importance of these parameters
based on well-resolved in-house large-eddy and direct numerical
simulations as well as wind tunnel experiments.
A recurring tool in the investigation of these topics is the
diagnostic-plot concept, which indicates a linear dependence between
the turbulence intensity and its mean velocity and turns out to be
useful when establishing a well-behaved state in the outer layer of
wall-bounded turbulent flows and determining the boundary layer edge
in strong PG cases or TBLs on curved surfaces. A possible analogy
between high-Re ZPG TBL flows and strong APG TBLs is also considered
in light of negative wall-shear stress events.
Dr. Ramis Örlü received his M.Sc. (Dipl-.Ing.) in 2003
from the Ruhr University of Bochum, Germany in Mechanical
Engineering and holds a Ph.D. in Fluid Mechanics (2009) KTH Royal
Institute of Technology, Stockholm, Sweden. His research is focused
on experimental methods and wall-bounded turbulent flows. Since 2009
and 2015 he works as a researcher and docent (in Experimental Fluid
Physics), respectively, at the Linné FLOW Centre located at
KTH. His research portfolio covers the experimental investigation
of wall-bounded turbulent flows with strong numerical
collaborations. Other active areas cover measurement technique
development/correction for high-Reynolds number wall-bounded flows
as well as applications in internal combustion engine related flows
and various flow control strategies for separation delay and
skin-friction drag reduction. Dr. Örlü has about 50
journal publications, and a wide network with other researchers in
wall-bounded turbulence research.
Experimental investigation of two-phase flows in naval hydrodynamics
Paul Brandner
Australian Maritime College University of Tasmania
4pm Thursday 29 September 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Flow about ships and submarines vary from pure liquid-gas to pure
liquid-vapour two-phase flows. They involve a large range of spatial
and temporal scales and physical phenomena such that gaining insight
remains a challenge via either experiment or computation. Naturally
occurring microbubble populations in the ocean are of particular
interest due to their potential to both affect and be affected by
various phenomena and flow processes. They provide nuclei for
cavitation inception on lifting surfaces of ships and submarines.
Surface ships are prolific sources of polydisperse bubble
populations that add to bubbly disperse flows about lifting
surfaces. Cavitation and turbulence ultimately create complex
long-lived large-scale microbubble laden wakes with properties
significantly altered compared with those of the outer fluid.
Techniques and results on various two-phase flow experiments in
naval hydrodynamics are presented including microbubble generation
for artificial seeding of nuclei and for PIV, microbubble disperse
flows, cavitation inception, macroscopic cavitation phenomena,
supercavitation, millimetre-bubble break and coalescence in
turbulent shear flows and fluid-structure interaction.
Paul Brandner is research leader of the Cavitation Research
Laboratory at the Australian Maritime College. His research
interests include cavitation inception and dynamics, bubbly flows,
supercavitation, fluid-structure interaction and hydroacoustics.
Completion: Numerical simulations of two-phase flow: Eulerian and Lagrangian predictions
Shuang Zhu
University of Melbourne
4.15pm Friday 16 September 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The term two-phase flow refers to any fluids flow of two coexisting
media in motion. The difference between the media can be its
thermodynamic state, called phase (e.g. gas, liquid or solid) and/or
its multiple chemical components. Two-phase flow is common in many
environmental systems including rain, snow, sandstorms, avalanches,
sediment transport debris flow and countless other natural
phenomena. It is also of extreme importance in many industrial and
engineering applications, such as fluidised bed, droplet spray
process, drug aerosol delivery, dense gas dispersion, particle
deposition and pollution control.
A persistent theme throughout the study of two-phase flow is the
need to model the detailed behaviour of these flow phenomena as the
ability to predict the behaviour of these flow systems is central to
safety, efficiency and effectiveness of those events and processes.
Similar to single-phase flow research, the development of predictive
models for the two-phase flow follows along three parallel paths,
namely theoretical models, laboratory experiments and numerical
simulations. There are some cases where full-scale experimental
models and/or accurate theoretical models are possible. However, in
many other cases, the use of those models can be impossible for many
of reasons. Consequently, the predictive capability and physical
understanding of two-phase flow problems heavily rely on the
employment of numerical simulations. The study of dynamics of
two-phase flow using high resolution numerical simulations has
gained considerable momentum with the recent development in
computational fluid dynamics (CFD) methodologies. In particular, the
use of direct numerical simulations (DNS) resolves the entire range
of spatial and temporal scales of the fluid motion, which provides
new insights into the structure and dynamics of the two-phase
flow.
Current two-phase flow simulations modelling can be broadly
classified based on the treatment of the dispersed phase. Two types
of approaches are prevalent, Eulerian approach and Lagrangian
approach, which are based on the concept of the continuous phase
described in the Eulerian reference frame in a flow domain with the
dispersed phase described either in the Eulerian reference frame as
the continuous phase, leading to the Eulerian approach (commonly
known as the "two-fluid" model), or in the Lagrangain frame, leading
to the Lagrangain approach (also known as the "trajectory" model).
The primary motivation behind the present work is to perform high
fidelity numerical simulations to study two-phase flow using both
Eulerian and Lagrangian approaches on three different two-phase flow
problems, namely gravity currents, particle-laden currents and
enhanced targeted drug delivery in a vascular tree.This PhD work
provides a much needed knowledge on different two-phase flow
numerical modelling approaches by solving the aforementioned real
life scenarios. Specifically, the success of this PhD work would
lead to better two-phase computational fluid dynamics
strategy.
Statistical characteristics of fully nonlinear potential deep water wave fields
Elena Sanina
Department of Infrastructure Engineering, University of Melbourne
4pm Friday 12 August 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
We present an analysis of long-term wave simulations performed using
a fully nonlinear potential deep water wave model. The results of
the simulations are compared with the spectra obtained using a
variety of directional methods and are discussed in the context of
their applications. The short-crestedness of a wave field is
investigated in terms of the three-dimensional steepness defined as
the vector whose magnitude is equal to the average steepness
calculated along the vector direction in a horizontal plane. Several
statistical characteristics of the surface elevation field and the
wave spectrum development such as a non-uniformity of the wave
spectrum and a migration of its peaks are discussed. The appearance
of coherent structures on the ocean surface closely related to the
tendency of high waves to occur in groups is analysed. Various
features of the identified groups such as velocity of the groups,
their lengths, lifetime and steepness are studied. A general
analysis of the number of detected groups is also performed for the
computed wave fields.
Dr. Elena Sanina is a Research Fellow in Ocean Engineering at the
Department of Infrastructure Engineering, University of Melbourne.
With Bachelor and Master degrees in Pure Mathematics from the
Voronezh State University (Russia), she continued her studies
performing research in the area of applied mathematics. In 2015
she completed her PhD in the Centre for Ocean Engineering, Science
and Technology (COEST) at Swinburne University of Technology, then
continued her work at the University of Melbourne in May 2016. Her
research interests include non-linear waves, extreme waves and wave
statistics.
Completion: Evolution of zero pressure gradient turbulent boundary layers
Will Lee
University of Melbourne
4pm Monday 8 August 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
An experimental investigation of evolving turbulent boundary layers in a tow
tank facility is presented. The main aim is to study the dynamics and the
development of coherent features in a turbulent boundary layer from the trip
to a high-Reynolds number state. With this goal in mind, time-resolved
particle image velocimetry measurements are performed with a towed plate to
provide a unique view of the streamwise evolution of turbulent boundary
layers. The merit of this temporally-resolved dataset is it enables us to
investigate the evolving dynamic properties of coherent features
specifically in the outer region of turbulent boundary layers. The results
reveal the formation mechanism and temporal evolution of shear layers and
their associated large-scale coherent motions. Based on these findings, a
conceptual model which describes dynamic interactions of coherent features
is proposed and discussed.
Self-sustaining motions and periodic orbits in statistically stationary homogeneous shear turbulence
Atsushi Sekimoto
Monash University
4pm Friday 5 August 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Homogeneous shear turbulence (HST) is the most canonical flow to investigate
the shear-induced turbulence, where it is known that there are coherent
structures, like velocity streaks and streamwise elongated vortices, similar
to wall-bounded flows. The coherent structures and their dynamics are
considered as incomplete realisations of nonlinear invariant solutions in
the incompressible Navier–Stokes equation, i.e. equilibrium solutions
or periodic orbits, which have been reported in the plane Couette,
Poiseuille, pipe flow, isotropic turbulence, and so on. In this study,
unstable periodic orbits (UPOs) in HST are investigated. The ideal HST grows
indefinitely, and in simulations, the growing integral scale reaches the
size of the computational domain. The largest-scale motion is restricted by
the computational domain, and it grows, break-downs, and regenerates
quasi-periodically, reminiscent to the self-sustaining motion and bursts in
wall-bounded flow. The long term simulation of HST reaches the statistically
stationary state. Direct numerical simulations (DNS) of statistically
stationary homogeneous shear turbulence (SS-HST) are performed by a newly
developed code. The box dependency is investigated to establish 'healthy'
turbulence in the sense that the turbulence statistics are comparable to
wall-bounded flow. SS-HST is essentially a minimal flow, and constrained by
the spanwise box dimension as in minimal channel flow (Sekimoto, Dong &
Jiménez, 2016 Phys. Fluids 28:035101; Flores &
Jiménez 2010 Phys. Fluids 22:071704). In these good boxes,
UPOs are numerically obtained. It represents a regeneration cycle of
streamwise vortices and a streak, similar to the self-sustaining process
(SSP) in wall-bounded flow.
The speaker received a PhD in thermo-fluid mechanics from Osaka University
in 2011. He joined the Fluid Mechanics group in the Technical University of
Madrid (UPM) as postdoctoral fellow. He is now a research fellow in the
Laboratory for Turbulence Research in Aerospace & Combustion (LTRAC) in
Monash University.
Fluid mechanic challenges at DST Group: from submarines to hypersonic vehicles
Malcolm Jones
Defence Science and Technology Group
4pm Friday 29 July 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The physics of fluid flow plays a dominant role in modelling vehicles
traveling through the atmosphere or oceans. Whether it is predicting the
drag experienced on a submarine, the lift generated by a flapping wing
micro air vehicle or the heating loads acting a hypersonic vehicle. The
Navier–Stokes equations governing these flows are known, but except
for a few trivial cases cannot be solved directly. For this reason a range
of alternative methods must be used. These include: approximations to the
equations, numerical solutions, laboratory scale experiments and field
trials. This talk will discuss how these methodologies are applied Defence
Science and Technology Group to three example research areas: submarine
hydrodynamics, flapping wing aerodynamics and hypersonic aerodynamics. While
these vehicles appear diverse there is a common theme in the technical
challenges and hence in the scientific approach taken.
Malcolm Jones received a PhD in fluid mechanics from The University of
Melbourne in 1998. He received a degree in mechanical engineering from the
same university in 1994. He joined the Defence Science and Technology Group
in 2007 where he is currently employed as a Research Scientist in the
Aerospace Division. Malcolm currently works on a range of diverse research
projects which include: aerodynamics of flapping wings, aerodynamics of
hypersonic vehicles (HIFiRE program), cavity aeroacoustics, boundary layer
transition, and submarine hydrodynamics. Prior to joining DSTO he was
employed as Research Fellow and lecturer in the Department of Mechanical
Engineering at The University of Melbourne and also at the School of
Mathematical Sciences, Queensland University of Technology.
Confirmation: DNS of a turbulent line plume in a confined region
Nitheesh George
University of Melbourne
4pm Thursday 28 July 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
We present results from a direct numerical simulation (DNS) of a turbulent
line plume in a confined region with adiabatic side, top and bottom walls.
The plume originates from a local line heat source of length, L, located at
the centre of the bottom wall (z/H = 0) and it rises until it hits the top
wall (z/H = 1) and spreads laterally to produce a buoyant fluid layer. Since
the region is confined, the continuous supply of buoyant fluid forces the
layer downwards, until it reaches the bottom wall, where the flow is said to
be the asymptotic state (Baines and Turner 1969). In the present case, two
Reynolds numbers, 3840 and 7680, are selected for plume lengths, L/H = 1, 2
and 4, where the Reynolds number of the plume is based on H and the buoyant
velocity scale, F01/3, where F0 is
buoyancy flux per unit length. The current simulations are validated
against the analytical model presented by Baines and Turner (1969). The
simulations exhibit a slow flapping motion of the confined line plume in the
asymptotic state, which precludes a straightforward comparison with Baines
and Turner's analytical model. For the purpose of comparing the analytical
model, we have adapted a shifting method introduced by Hubner (2004), which
improves agreement with the analytical model.
Confirmation: Optimal actuator and sensor placement for feedback flow control using the complex Ginzburg–Landau equation
Stephan Oehler
University of Melbourne
4pm Friday 8 July 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The process of selecting the optimal actuator and sensor positions for a
single-input single-output flow control problem is investigated and its
limitations are discussed. Multiple unstable modes and time delays between
actuating and sensing often result in a challenging flow control problem.
Previous approaches have focused on the use of modern control schemes, but
these do not always provide the full picture and difficult control problems
are often predicated on fundamental limitations, which are not made clear in
a modern control framework. In this paper, a previously developed control
scheme for the complex Ginzburg–Landau equation is presented, the
challenges for different set-ups are analysed and it is shown how
fundamental limitations can lead to an intractable control problem. The
research explores the control schemes developed for the complex
Ginzburg–Landau equation from the fundamental perspective, while
further connecting the two fields of fluid dynamics and control theory.
The mitigation of pulsation in ventilated supercavities
Grant Skidmore
University of Melbourne
4pm Friday 1 July 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
It is possible for an underwater body to greatly reduce the drag caused by
skin friction, using ventilated supercavitation. While the idea of
ventilated supercavitation works well in theory, the process of generating
a ventilated supercavity in practice is often plagued by pulsation. When a
supercavity pulsates, the walls of the supercavity begin to periodically
expand and contract. This can lead to the supercavity walls clipping the
body, which can become problematic for stability of the supercavitating
body. This seminar will explore the internal cavity pressure and near-field
noise generated by experimental and computational supercavities. The results
of the acoustic study revealed that the radiated acoustic pressure of
pulsating supercavities is at least 40 dB greater than comparable twin
vortex and re-entrant jet supercavity closure regimes. For pulsating
supercavities it was also found that, at the pulsation frequency, the cavity
interior pressure spectrum level was related to the near-field and far-field
noise spectrum level through spherical spreading of the sound waves from the
supercavity interface. As a result, the cavity interior pressure can be used
as a measure of the radiated noise. The oscillatory nature of the internal
cavity pressure time history was used to develop a method to mitigate
supercavity pulsation. The method was explored with a numerical model,
experiments, and CFD. The method is based on modulating the ventilation rate
injected into a ventilated supercavity with the addition of a sinusoidal
component. The effect of this modulation is the ventilated supercavity being
effectively driven away from the resonance frequency. A wide range of
ventilation rate modulation frequencies can cause the pulsating supercavity
to transition into twin vortex closure. A reduction in the radiated noise
accompanies the transition from pulsation to twin vortex closure, oftentimes
35 dB or more. Other modulation frequencies do not suppress pulsation but
change the supercavity pulsation frequency.
Grant Skidmore is a postdoctoral researcher in Mechanical Engineering at the
University of Melbourne. Grant obtained his PhD in aerospace engineering
at the Pennsylvania State University. His research interests include
supercavitation, drag reduction, hydrodynamic stability, free surface flows,
multiphase flows, and turbulent wakes.
Confirmation: Geometric aspects of wall-flow dynamics
Rina Perven
University of Melbourne
4pm Tuesday 28 June 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Complex but coherent motions form and rapidly evolve within wall-bounded
turbulent flows. Research over the past two decades broadly indicates that
the momentum transported across the flow derives from the dynamics
underlying these coherent motions. This spatial organization, and its
inherent connection to the dynamics, motivates the present dissertation
research. The local field line geometry pertaining to curvature (κ)
and torsion (τ) has apparent connection to the dynamics of the flow, and
preliminary results indicate that these geometrical properties change
significantly with wall-normal position. One part of this research is thus
to clarify the observed changes in the field line geometry with the known
structure and scaling behaviours of the mean momentum equation. Towards this
aim, the planar curvature of the streamlines at each point in
streamwise–spanwise slices of existing boundary layer DNS has been
computed for different wall-locations. The computation of κ and τ
arise from the local construction of the Frenet–Serret coordinate
frame. The present methods for estimating κ and τ are briefly
described, as is the need to improve the efficiency of this computation. The
present results are briefly described, as are the broader aims to better
understand the relationships between the geometry and dynamics of
wall-flows. A schedule of the future work to be conducted is outlined.
Laser light sheet profile and alignment effects on PIV performance
Kristian Grayson
University of Melbourne
11am Monday 27 June 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The sensitivity and impact of laser profile misalignment and shape mismatch
on Particle Image Velocimetry (PIV) measurements are investigated in this
study. While the effects of laser profile misalignment can be equivalent to
an out-of-plane velocity component, light sheet mismatch can be identified
and corrected prior to an experiment, decreasing PIV uncertainties.
Synthetic particle image simulations are used to isolate and systematically
vary laser profile mismatch parameters between successive PIV laser pulses.
Two simulation cases are discussed, analysing the effects of a misalignment
between two otherwise identical laser pulses, as well as a mismatch in the
width of two laser profiles. Our results reveal a steady degradation in mean
correlation coefficient as the laser profiles are increasingly mismatched in
shape and alignment, coupled with a rapid rise in the detection of spurious
vectors. These findings reinforce the need to consider laser sheet alignment
and intensity distribution when seeking to capture high quality PIV
measurements. The design of a modular and inexpensive laser profiling camera
is outlined to enable robust and repeatable quantification of laser sheet
overlap and beam characteristics. The profiling system is also found to be
a valuable tool for laser diagnostics and aiding the setup of experiments.
Various potential applications of this device are presented for PIV and
other laser-based measurement techniques. Finally, preliminary results from
PIV experiments which involve the deliberate misalignment of laser profiles
are discussed. These data reiterate the trends observed in simulations, but
also emphasise the coupled complexity of laser profile mismatch behaviour in
experimental scenarios, placing the idealised simulation results in some
context. Collectively, our findings highlight the importance of well-matched
laser profiles. A more rigorous experimental quantification of these
behaviours has the potential to enhance the quality of PIV results.
Towards a Moody-like diagram for turbulent boundary layers
Dale Pullin
Graduate Aerospace Laboratories, California Institute of Technology
4pm Friday 24 June 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
An empirical model is presented that describes a fully developed turbulent
boundary layer in the presence of surface roughness with a nominal roughness
length-scale that varies parametrically with stream-wise distance. For
Reynolds numbers based on the outer velocity and stream-wise distance that
are large, use is made of a simple model of the local turbulent
mean-velocity profile that contains the Hama roughness correction for the
asymptotic, fully rough regime. It is then shown that the skin friction
coefficient is constant in the streamwise direction only for a linear
streamwise roughness variation. This then gives a two parameter family of
solutions for which the principal mean-flow parameters can be readily
calculated. Results from this model are discussed for the
zero-pressure-gradient turbulent boundary layer, and some comparisons with
the experimental measurements of Kameda et al. (2008) are made.
Trends obtained from the model are supported by wall-modeled, large-eddy
simulation (LES) of the zero-pressure-gradient turbulent boundary layer at
very large Reynolds numbers. Both model and LES results are consistent with
the self-preservation arguments of Talluru et al. (2016). It is
argued that the present model/LES can be interpreted as providing the
asymptotically rough-wall equivalent of a Moody-like diagram for turbulent
boundary layers in the presence of small-scale wall roughness.
The speaker is the von Kármán Professor of Aeronautics at the
California Institute of Technology. His research interests include
computational and theoretical fluid mechanics, vortex dynamics, compressible
flow and shock dynamics, turbulence, and large-eddy simulation of turbulent
flows.
The universal nature of freestream coherent structures
Philip Hall
Monash University
4pm Friday 17 June 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Exact coherent structures are nonlinear solutions of the Navier Stokes
equations not necessarily arising as bifurcations from a base state. The
solutions are thought to be relevant to bypass transition and fully
turbulent flows. There are two fundamental types of solutions: vortex-wave
interaction states and freestream coherent structures. A brief survey of the
field is given and then freestream coherent structures are discussed in
detail. These are shown to be driven in a nonlinear layer located where the
base flow adjusts to its freestream value through exponentially small terms.
It is shown that they are implicated in the production of passive near wall
streaks in a layer distant log R from the wall where R is the Reynolds
number. They are shown to be canonical states relevant to any 2D boundary
layer, vortex sheet, jet or wake and relevant to weakly 3D forms of the
latter flows. Remarkably it turns out that they also exist in any fully
developed flow having a local maximum of the unperturbed velocity field. The
relevance to fully turbulent flows is discussed.
Professor Philip Hall is the Head of School of Mathematics, Monash
University. Professor Hall is presently on leave from Imperial College,
where he became the first Director of the Institute of Mathematical Sciences
and where he has been the Director of LFC (Laminar Flow Control)-UK. His
research interests are in applied mathematics, particularly in nonlinear
hydrodynamic stability theory, computational fluid dynamics, boundary layer
control, convection, lubrication theory, chaotic fluid motion, geomorphology
of rivers and coherent structures in high Reynolds number flows.
A voyage from the shifting grounds of existing data on zero-pressure-gradient turbulent boundary layers to infinite Reynolds number
Hassan M. Nagib
Illinois Institute of Technology, Chicago, USA
4pm Friday 10 June 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Aided by the requirement of consistency with the Reynolds-averaged momentum
equation, the 'shifting grounds' are sufficiently consolidated to allow some
firm conclusions on the asymptotic expansion of the streamwise normal stress
normalized with the friction velocity; i.e.
<u+u+>. A detailed analysis of direct numerical
simulation data very close to the wall reveals that its inner near-wall
asymptotic expansion must be of the form f0(y+)
− f1(y+) / U∞+
+ O(U∞+)−2, where f0
and f1 are O(1) functions fitted to data. This means, in
particular, that the inner peak of the normal stress does not increase
indefinitely as the logarithm of the Reynolds number but reaches a finite
limit. The outer expansion of the normal stress
<u+u+>, on the other hand, is constructed by
fitting a large number of data from various sources. This exercise, aided
by estimates of turbulence production and dissipation, reveals that the
overlap region between inner and outer expansions of
<u+u+> is its plateau or second maximum,
extending to ybreak+ =
O(U∞+), where the outher logarithmic decrease
towards the boundary layer edge starts. The common part of the two
expansions of <u+u+>, i.e. the height of the
plateau or second maximum, is of the form A∞ −
B∞ / U∞+ + ... with
A∞ and B∞ constant. As a consequence, the
logarithmic slope of the outer <u+u+> cannot be
independent of the Reynolds number as suggested by 'attached eddy' models
but must slowly decrease as 1 / U∞+. A
speculative explanation is proposed for the puzzling finding that the
overlap region of <u+u+> is centered near the
lower edge of the mean velocity overlap, itself centered at y+
= O(1 / Reδ*0.5) with
Reδ* the Reynolds number based on free stream
velocity and displacement thickness. Similarities and differences between
<u+u+> in ZPG TBLs and in pipe flow will be
briefly discussed. Finally, the composite profile of
<u+u+> is used with our mean velocity composite
profile to demonstrate the detailed behavior of the so-called "diagnostic
plot" with Reynolds number.
Professor Nagib is the John T. Rettaliata Distinguished Professor of
Mechanical and Aerospace Engineering at the Illinois Institute of
Technology, Chicago, Illinois, and the Founding Director of the
Institute's Fluid Dynamics Research Center. His field of specialty is in
fluid mechanics, turbulent flow and flow management and control. Professor
Nagib is the recipient of a number of prestigious honors including being a
Fellow of the American Physical Society, the American Association of
Advancement of Science, the American Institute of Aeronautics and
Astronautics, and the American Society of Mechanical Engineers.
Large-amplitude flapping of an inverted-flag in a uniform steady flow
John E. Sader
School of Mathematics and Statistics, University of Melbourne
|
Website
4pm Friday 3 June 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The dynamics of a cantilevered elastic sheet, with a uniform steady flow
impinging on its clamped-end, have been studied widely and provide insight
into the stability of flags and biological phenomena. Recent measurements
show that reversing the sheet's orientation, with the flow impinging on its
free-edge, dramatically alters its dynamics. In contrast to the conventional
flag, which exhibits (small-amplitude) flutter above a critical flow speed,
the inverted-flag displays large-amplitude flapping over a finite band of
flow speeds. In this talk, a combination of mathematical theory, scaling
analysis and measurement is used to investigate the origin of this
large-amplitude flapping motion. Flapping is found to be periodic
predominantly, with a transition to chaos as flow speed increases. These
findings have implications to leaf motion and other biological processes,
such as the dynamics of hair follicles, because they also can present an
inverted-flag configuration. This collaborative work is with the Gharib
group at the California Institute of Technology.
John E. Sader is a Professor in the School of Mathematics and Statistics,
The University of Melbourne. He leads a theoretical group studying a range
of topics including the dynamic response of nanoparticles under femtosecond
laser excitation, mechanics of nanoelectromechanical devices, high Reynolds
number flow of thin films and rarefied gas dynamics in nanoscale systems.
Turbulent horizontal convection and heat transfer
Bishakhdatta Gayen
Research School of Earth Sciences, Australian National University
|
Website
4pm Friday 27 May 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Horizontal convection (HC) is driven by a horizontal difference in
temperature or heat flux at a single horizontal boundary of a fluid. In a
thermally equilibrated state, net heat flux over the boundary is zero and
circulation cell involves a horizontal boundary flow, turbulent plume motion
at the end wall, and interior return flow which covers the entire the flow
domain. HC may be a simple model of the meridonial overturning circulation
(also known as global thermohaline circulation) based on such convective
flow.
I will present three-dimensional convective circulation under differential
heating on a single horizontal boundary of a rectangular channel, using
direct and large eddy simulations over a wide range of Rayleigh numbers,
Ra ∼ 10
8–10
15. A sequence of several
stability transitions lead to a change from laminar to fully developed
turbulent flow. At the smallest Ra, convection is maintained by a balance of
viscous and buoyancy forces inside the thermal boundary layer, whereas at
the largest Ra, inertia dominates over viscous stresses. This results in an
enhancement of the overall heat transfer at Ra ≥ 10
10, while
both dynamical balances give Nu ∼ Ra
1/5. We have recently
extended our study on circulation by applying thermal forcing on a
lengthscale smaller than the domain, and with variation in both horizontal
directions instead of traditional unidirectional gradient over the domain
scale. Simulations show turbulence throughout the domain, a regime
transition to a dominant domain-scale circulation, and a region of
logarithmic velocity in the boundary layer. Scaling theory shows a new
regime dominated by inertia of the symmetric interior large scale
circulation, coupled to thermal dissipation in the boundary layer which
explains the Nu ∼ Ra
1/4 behaviour.
Finally, I will show circulation in a rotating rectangular basin forced by a
surface temperature difference but no wind stress. Here, our focus is on the
geostrophic regime for the horizontal circulation with a strong buoyancy
forcing (large Ra).
Buoyancy effects on turbulent entrainment
Dominik Krug
University of Melbourne
4pm Friday 6 May 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
In this talk, we will address the question which role buoyancy plays in the
entrainment process in unstable configurations such as turbulent plumes.
Based on data from direct numerical simulations of a temporal plume we show
that the entrainment coefficient can be determined consistently using a
global entrainment analysis in an integral framework as well as via a local
approach. The latter is based on a study of the local propagation of the
turbulent/non-turbulent interface (TNTI) relative to the fluid. We find that
locally this process is dominated by small-scale diffusion which is
amplified by interface-convolutions such that the total entrained flux is
independent of viscosity. Further, we identify a direct buoyancy
contribution to entrainment by the baroclinic torque which accounts for
8–12% percent of the entrained flux locally, comparable to the buoyancy
contribution at an integral level (15%). It is concluded that the effect of
the baroclinic torque is a mechanism which might lead to higher values of
the entrainment coefficient in spatial plumes compared to jets. Finally,
some results will be presented from applying the local analysis to a stable
configuration. Here, buoyancy is observed to reduce the entrainment rate by
reducing the surface area of the TNTI and we will consider how this affects
the fractal scaling.
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Measuring ocean turbulence and inferring ocean mixing
Greg Ivey
University of Western Australia
4pm Friday 29 April 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Conversion: Experimental factors influencing the quality of PIV results
Kristian Grayson
University of Melbourne
2pm Wednesday 27 April 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Particle Image Velocimetry (PIV) is a useful tool for investigating the
behaviour of turbulent flows, enabling the capture of undisturbed
instantaneous velocity fields. The shape and alignment of the pulsed laser
sheets used in PIV can have a significant impact on the quality of results,
where laser profile mismatches can degrade correlation quality. This study
develops two key experimental and analysis tools to aid the refinement of
PIV techniques and systematically quantify the impact of unoptimised laser
characteristics. Improvements to PIV simulation software enable much more
experimentally realistic scenarios to be modelled and a laser profiling
camera allows laser characteristics and alignment to be quantified in
experimental setups for troubleshooting and analysis. The capabilities of
these tools can ultimately be used to assess the practicality and possible
benefits of more advanced and complex experimental PIV configurations.
Symmetries and symmetry breaking in bluff-body wakes
Justin Leontini
Swinburne University of Technology
4pm Friday 22 April 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
The periodic vortex shedding in the wake of a circular cylinder is one of
the most well-studied flows in fluid mechanics. It often serves as a
canonical flow for understanding all bluff-body flows, as well as being
important in its own right due to the common use of cylindrical cross
sections in engineering structures. The periodic forcing on the structure
caused by this vortex shedding can lead to large correlated forces and
subsequent vibration. Often, it is desirable to control this motion to avoid
failure; at other times, this motion may be deliberately amplified to be
used as a source of energy harvesting. Here, I will present results looking
at simple control strategies of this wake, such as periodic forcing and
geometrical modifications such as streamlining. I will show that even these
simple modifications to the base cylinder flow can result in significant
changes in the flow, and that many of these changes can be understood by
considering the interaction of the symmetries of the base flow and the
imposed control.
Dr. Justin Leontini joined Swinburne in December 2013. Previous to this, he
was an Australian Postdoctoral Fellow at Monash University, spent time
working at the Centre for Maths and Information Science at CSIRO, and at
l'Institut de la Recherche sur les Phenomenes Hors Equilibre (IRPHE)
(trans. Dynamic Systems Research Institute) in Marseille, France. His
research work has spanned fundamental fluid-structure interactions,
planetary core flows, ship hydrodynamics, and flow stability. Recently, he
has been building a project investigating the gas transport mechanisms in
specialty ventilation machines in neonatal ICU wards. All of this research
is focussed around understanding the fundamental physics of flow phenomena
that have relevance to engineering or natural problems.
Direct and large eddy simulations of flows through low-pressure turbines subject to inlet disturbances
Richard Pichler
University of Melbourne
4pm Friday 15 April 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
To reduce specific fuel consumption and cost of jet engines it is
desirable to decrease the number of blades. As a result the individual
blades of modern low-pressure turbines (LPT) are subjected to more
severe pressure gradients that might lead to flow separation. Since
laminar boundary layers are more prone to separation than turbulent
ones, the actual transition location might dictate if a boundary layer
remains attached or not, which in general has a significant effect on
losses.
Transition is known to be influenced by the incoming flow state, in
particular inlet turbulence and discrete wakes shed by the upstream
blade row(s) that in essence are regions of high-turbulence and
low-momentum flow. To investigate the interaction of unsteady transition
and separation for varying design parameters, a combined large-eddy and
direct numerical simulation study has been conducted and the data have
been studied in light of loss generation.
The control of near-wall turbulence by non-conventional surfaces
Ricardo García-Mayoral
University of Cambridge |
Website
4pm Friday 8 April 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Complex features on what would otherwise be a smooth wall can alter an
overlying turbulent flow. This talk will focus on surfaces that exploit
this capability to reduce wall friction, and will discuss three of such
surfaces: riblets, permeable and superhydrophobic surfaces. Riblets are
a kind of directional roughness made up of small surface grooves aligned
in the direction of the flow. Permeable coatings allow the flow to
penetrate into the surface to a certain extent. Superhydrophobic
surfaces, when immersed in water, can entrap pockets of air, so that the
water flow can effectively slip over them. In all cases, for small
texture or pore size the reduction of friction increases with size, but
beyond a certain size the performance begins to degrade, limiting the
range of technological interest and the optimum performance achievable.
The talk will discuss both the drag-reducing and the drag-degrading
mechanisms for the above three types of surface.
Universality aspects and coupling mechanisms of turbulence
Patrick Bechlars
University of Melbourne
4pm Friday 1 April 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
To understand, describe and model the physical processes that drive a
chaotic turbulent flow a comprehensive and detailed understanding of flow
features and their interconnection is needed. This can be obtained through
a thorough analysis that interprets and breaks down observations across
different flows and locations. This should be done to expose key features
of turbulence from different points of view. The features then need to be
connected to create the solution of the puzzle.
With this in mind a set of detailed time-resolved 3D flow data was sampled.
The set involves data from a turbulent boundary layer, turbulent pipe
flows, jet flows and a supersonic wake flow. I am happy to share these
datasets and look forward to upcoming collaborations.
Besides an outline of the available datasets, some universal and
non-universal aspects of turbulence across the different flows will be
discussed in the presentation. Further, an analysis based on the velocity
gradient invariant is applied to discuss the composition and development
of turbulence across a turbulent boundary layer flow. Also, the method was
extended to analyze the cascading process of kinetic energy. This analysis
exposes the backscatter mechanism that transfers kinetic energy from smaller
to larger scales of motion. Results for this will be shown and an underlying
physical mechanism will be suggested.
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Completion: Structure of mean dynamics and spanwise vorticity in turbulent boundary layers
Caleb Morrill-Winter
University of Melbourne
3.30pm Thursday 24 March 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
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Conditional methods for modelling turbulent combustion
Alexander Klimenko
University of Queensland
4pm Friday 18 March 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
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High-fidelity simulations of noise radiation from an elastic trailing-edge
Stefan Schlanderer
University of Melbourne
4pm Friday 11 March 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
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A model problem for a supersonic gas jet from a moon
Hans Hornung
California Institute of Technology
4pm Friday 4 March 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
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Computing external flows with the immersed boundary method and the lattice Green's function
Tim Colonius
California Institute of Technology
3pm Friday 26 February 2016
Old Metallurgy Masters Seminar Room 2 (Room 202, Bldg 166)
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Coherent features in jet aero-acoustics and wall-bounded turbulence
Woutijn Baars
University of Melbourne
4pm Friday 19 February 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
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Dynamics of impacting slot jets
David Lo Jacono
Institut de Mécanique des Fluides de Toulouse
4pm Friday 12 February 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
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Investigation of supercritical airfoil dynamic response due to transonic buffet
Robert Carrese
RMIT University
Transition prediction for non-axisymmetric bodies of revolution
David Pook
Defence Science and Technology Group
4pm Friday 22 January 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
