Snezhana Abarzhi
University of Western Australia
3.30pm Friday 9 February 2018
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
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
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Thermoacoustic instabilities frequently appear in various combustion systems
in the form of highamplitude 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 highefficiency, lowemission 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, loworder modeling and stability analysis,
pulsed detonation, and plasmaassisted combustion.
Color of turbulence
Mihailo Jovanovic
University of Southern California
3.30pm Monday 18 December 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
This talk describes how to account for secondorder statistics of turbulent
flows using lowcomplexity stochastic dynamical models based on the
linearized NavierStokes (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 secondorder statistics in a way that is consistent with
linearization around turbulent mean velocity. In general, whiteintime
stochastic forcing is not sufficient to explain turbulent flow statistics.
We develop models for coloredintime forcing using a maximum entropy
formulation together with a regularization that serves as a proxy for rank
minimization. We show that coloredintime excitation of the NS equations
can also be interpreted as a lowrank modification to the generator of the
linearized dynamics. Our method provides a datadriven 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 largescale structures in turbulent Rayleigh–Bénard Convection
Yulia Peet
Arizona State University
11.30am Friday 15 December 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
At high Rayleigh numbers in moderate aspectratio cylindrical domains
turbulent Rayleigh–Bénard convection (RBC) exhibits coherent
largescale motions that organize themselves into a collection of
threedimensional "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
9.6×10^{7}. The analysis of the longtime 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 hubandspoke mode3 pattern
first emerges and dominates the flow for the first 20 eddy turnovers, which
then transitions into a mode2 pattern that persists for the remainder of
the simulations. A spatial inhomogeneity of the observed mode3 and mode2
structures is investigated. A conclusion follows that the cylindrical
geometry constraint applies a "squeezing" effect to the largescale
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 highperformance 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 modelbased wind
farm control approach for tracking a timevarying power signal such as a
frequency regulation command. The underlying timevarying 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
modelbased receding horizon control framework leads to a controlled wind
farm that qualifies to participate in markets for correcting shortterm
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 upregulation 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 largescale
networked systems in applications such as wallbounded 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 infrared 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 infrared 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 airbreathing propulsion, and
infrared 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
crosscorrelation of velocity and concentration reveal the organisation of
flow structures and the meandering plume. The timeaveraged streamwise
concentration flux is found to be positive and negative respectively, below
and above the plume centreline. This behaviour is a result of wallnormal
velocity fluctuations and Reynolds shear stress that play a dominant role in
the vertical spread of scalar plume. Results of crosscorrelation
coefficient show that high and lowmomentum regions have a distinctive role
in the transport of passive scalar. Above the plume centreline, lowspeed
structures have a lead over the meandering plume, while highmomentum
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 largescale 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 industrylinked 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
postdoctoral 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 farreaching 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 largescale coherent structures in a high Reynoldsnumber 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 largescale coherent structures in the outer region of a
highReynoldsnumber 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 wallnormal height, with these high and
lowspeed regions accompanied by respective down and upward wallnormal
velocity components. In a conditional sense, counterrotating roll modes are
manifested in the spanwisewallnormal planes.
In this talk, results of a realtime drag reduction strategy will be
presented where actuation involves using wallnormal jets. For an actuation
strategy where the jets are synchronized with the highspeed regions results
in a reduction of the energy associated with the largescale structures in
the outer region (∼30% reduction of largescale spectral energy was
observed in the logregion). Additionally, a maximum mean wallshear 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 lowspeed events show that the
abovementioned results are not a byproduct of the injection of the
wallnormal jet airflow into the turbulent boundary layer, rather it is due
to the implicit synchronization with the downwash sections of the
counterrotating roll modes which accompany the highspeed 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 finitetime 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 shipbased 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 semidiurnal tidal cycle and generally persisted for 4 h,
with periods ranging from 10–30 minutes. The NLIWs were not
consistently phaselocked 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 midwater column compared with the nearbed, 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 overpredict
and underpredict 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
macrotidal environment; Ocean mixing; The role of nonlinear 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 reducedorder 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 timeseries 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 reducedorder 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 threedimensional flow in a liddriven cavity,
(ii) an oscillatory flow past a square cylinder and (iii) a turbulent pipe
flow.
The second part will explore how to control selfsustained oscillations
using a datadriven 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 selfsustained
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 reducedorder 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
nearsurface 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 fireatmosphere 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 Reynoldsaveraged Navier–Stokes (RANS or
URANS) description of the flow. These include the
γ–Re_{θ,t} and laminarkineticenergy (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
noncontinuum, low Mach number regime. As the continuum assumption
underpinning the NavierStokes equations is violated, these flows must be
modelled using an approach that accounts for the noncontinuum 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 frequencydomain
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 timedomain, providing direct access to amplitude and phase
information using a pseudosteady algorithm. This frequencydomain method is
shown to provide a significant improvement in computational speed compared
to existing timedomain 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 HauniWerke 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 LandGrant Professorship (1994), and the NSF National
Young Investigator Award (1994). She serves as EditorinChief 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 (20112015) and
Associate Editor of Physics of Fluids (20082013).
Completion: Subminiature hotwire 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 wallbounded 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 hotwire 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 (nanoscale 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
hotwires. This enables us to acquire fullyresolved velocity measurements
of turbulent boundary layers up to a friction Reynolds number of 20,000.
Wallresolved largeeddy simulation of flow about smoothwalled and spanwise 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)
Wallresolved largeeddy simulation (LES) of flow over both smooth and
groovedwalled cylinders will be discussed. The stretchedvortex subgrid
scale model is embedded in a general fourthorder finitedifference code
discretization on a curvilinear, bodyfitting 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 smoothwalled and groovedwall cylinder flows exhibit
meanflow secondary separation bubbles embedded within the largescale,
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 smoothwall flow this is associated with
local transition to turbulence and a strong drag crisis. For the
groovedcylinder 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 largeeddy
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:
separationinduced 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 RANSbased
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 wakeloss profiles. This is partly due to
the use of the Boussinesq approximation to derive stressstrain
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 wakemixing and consequently wakeloss 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 wallbounded 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 wallturbulent 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, hotwire
measurements were performed over surfaces with spanwise heterogeneous
roughness with a certain halfwavelength 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 nearwall 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 1D 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 convectiondriven 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
10^{5}–10^{9} 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 RayleighBénard convection, a pure powerlaw
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
laminarlike boundary layers coexist with local nearwall 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 bulkdominated thermal convection and we show that the Nusselt
number versus Rayleigh number scaling relation instead follows the 1/2
powerlaw 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 wallbounded 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 crossslot
type microfluidic device equipped with an advanced imagebased realtime
control system and simultaneously quantified by micronresolution particle
image velocimetry (microPIV). This enables us to monitor potential
morphological damage to, and simultaneously compute the forces on, filaments
in realtime 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 zeronetmassflux actuators that can be used in a range
of flow control applications. For several pulsed/synthetic jet in crossflow
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 lowmomentum 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
lowReynoldsnumber 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 BiotSavart 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 crossflow.
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 longterm, 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 (bluegreen algae) and other microorganisms. 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
timescale tactical responses such as an environmental flow release from
upstream reservoirs in response to drought or heatwave conditions in order
to maintain water quality and river health. It will also enable them to
better optimize longterm water management strategies such as the
distribution of water allocations amongst stakeholders, taking into account
predicted changes in landuse 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 < Re_{Γ} < 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 secondorder 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
nonbuoyant 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 gravitycapillary 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 smallamplitude, stable flow pattern can be achieved in stationary
(rotating) twodimensional wave fields that are produced by
phasesynchronised 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 hightemperature 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: Airsea interaction: laboratory study on the airside turbulence of windwave
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. Airsea interaction is relevant to understanding
the coupled atmosphereocean system. The interactions involve small and
largescale transfers of momentum, heat and mass, which affect our weather
and climate. The knowledge of airsea 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 airside turbulence above
wind generated waves at the Extreme AirSea 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 soughtafter
measurements in the study of airsea interaction (Donelan et al.
1993).
Dynamic behaviours of composite panel subjected to underwater blast: fluidstructure 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 highperformance 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 fluidstructure interaction to understand the deformation and
failure mechanisms of both monolithic and Eglass/Vinylester/H250 PVC
sandwich composite panels. The experimental setup simulates fluidstructure
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 Laserinduced 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 ONRfunded 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, CRCProject and other
defencerelated 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
biomimicry 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
reemitted 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.
Adjointbased 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
nontrivial tasks such as flow control. To this end, an adjointbased
optimal flow control framework for compressible flows has been appended to
an existing inhouse 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 quasiincompressible 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 adjointbased 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 twofluid 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 laserdriven 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 RichtmyerMeshkov 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 twofluid, ionelectron,
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 highwavenumber instability. Consequently,
the density interface is substantially more unstable than predicted by the
Euler equations for all cases investigated. Selfgenerated 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 twofluid plasma simulations reveal that while the RMI is
suppressed in the presence of the seed field, the suppression mechanism
varies depending on the plasma lengthscales. Twofluid plasma RMI
simulations also reveal that the secondary, highwavenumber, electrondriven
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 postdoctoral
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.
Nonlaminar 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 NavierStokes equations have been found for canonical wallbounded
flows such as Couette, channel, and pipe flows at low Reynolds numbers
(~ 400). The defining characteristic of these solutions is the vortexstreak
structure that is known to play a crucial role in sustaining nearwall
turbulence. In statespace, some of these solutions lie in the region that
is densely visited by turbulence, while some others resemble the laminar
solution and regulate laminarturbulent transition. These solutions, along
with their connections in statespace, form a skeleton for trajectories of
turbulent flow. In addition to providing a description of turbulence
dynamics, this approach also produces an equationbased, lowrank basis for
use in flow control.
This vision of turbulence has not been extended to roughwalled 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
smoothwalled flows using a simple domain transformation method. We find
that the principal role of such grooves is to localize the vortexstreak
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 ribletmounted 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 surfaceroughness on the nearwall 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
TechnologyMadras, 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 wallbounded turbulence.
LES for loss prediction in an axial compressor cascade at offdesign 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
poststenting 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 twodimensional
axisymmetric arterial models with stents struts of square and circular
crosssectional 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
threedimensional 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). Timeaveraged 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 mobileboundary 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 multiscale
roughness elements and their mobility. These effects are especially profound
in the nearbed 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 nonfluid 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 doubleaveraged conservation equations are
developed for fluid, sediment, and plant motions. Complementary equations
for the secondorder velocity moments introduced by the averaging process
are also proposed. Due to the doubleaveraging methodology (i) the governing
equations are upscaled to the scales relevant to applications, (ii) the
fluid motion is rigorously coupled with the nonfluid (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 doubleaveraged equations outlined above, discusses
their application to the analysis of highresolution data sets and
identifies potential applications in mobileboundary flow studies.
Konstantinos performed his PhD research on flowbiota and flowsediment
interactions in rivers and openchannel flows at the University of Aberdeen,
where he was on a MarieCurie 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 iceshelves 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 sealevel 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 nonhydrostatic 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 highresolution 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 bluffbody, yet Strouhal never encountered a
vortex. I will try to show the role played by various wellknown 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
19th20th 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 18701970" celebrating the IMFT century anniversary.
Skinfriction and vorticity fields in wallbounded 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 noslip 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 "noslip tensor". Employing surface flow patterns
generated using local solutions of the NavierStokes equations, the
relationship between the surface skinfriction 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 largescale structures in channel flow at Re_{τ} = 1000
Simon Illingworth
University of Melbourne
4pm Friday 3 March 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Given the timeresolved velocity field in a plane at a single wallnormal
height, how well can one estimate, using a linear model alone, the
timeresolved velocity field at other wallnormal heights? This question
will be explored for channel flow at Re_{τ} = 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.
Subfilterscale stress modelling for largeeddy simulations
Amirreza Rouhi
University of Melbourne
4pm Friday 24 February 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
A subfilterscale (SFS) stress model is developed for largeeddy simulations
(LES) and is tested on various benchmark problems in both wallresolved and
wallmodelled LES. The basic ingredients of the proposed model are the model
lengthscale, and the model parameter. The model lengthscale 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 userdefined
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, backwardfacing step and separating boundary layer.
In wallresolved LES, both global and local models perform quite accurately.
Due to their nearwall behaviour, they result in accurate prediction of the
flow on coarse grids. The backwardfacing step also highlights the advantage
of decoupling the model lengthscale from the mesh. Despite the sharply
refined grid near the step, the proposed SFS models yield a smooth, while
physically consistent filterwidth distribution, which minimizes errors when
grid discontinuity is present.
Finally the model application is extended to wallmodelled LES and is tested
on channel flow and separating boundary layer. Given the coarse resolution
used in wallmodelled 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 walllayer
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
subfilterscale (SFS) stress modelling as his PhD thesis. His other research
interests include wallmodelled LES, spectral methods and rotating
turbulence.
Completion: The minimalspan channel for roughwall 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
semiempirical 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 roughwall studies. However, these techniques
are expensive for both industry and researchers, making design predictions
and the examination of roughwall flows challenging. In this talk, we
outline a framework termed the minimalspan channel in which fully resolved
numerical simulations of roughwall flows can be conducted at a reduced cost
compared to conventional DNS. The minimalspan 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 dtype 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
transitionallyrough surface patterns in the form of herringbone riblets.
The flow fields are investigated experimentally using large fieldofview
particle image velocimetry in all orthogonal planes. The pronounced
modification of the boundary layer suggests that a preferential arrangement
of the naturallyoccurring 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, nonsymmetrical vortical motions and strong streamwiseperiodic
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 smoothwall (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
3D 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 socalled "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 roughwall 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 roughwall turbulent boundary
layers spanning a very wide range of friction and roughness Reynolds
numbers. The results comprise 38 datasets and four experimental techniques,
including hotwire anemometry and particle image velocimetry. Our analysis
will focus broadly on the relationship between the outer region flow and
nearwall structures which are directly influenced by the roughness
scale(s). Features of this relationship will be discussed using
singlepoint statistics, measures of spatial structure, and the innerouter
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 nonbuoyant 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 nonexistent. 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 nonuniform
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.
Pulseburst PIV in highspeed flows
Steven Beresh
Aerosciences Department Sandia National Laboratories
4pm Wednesday 26 October 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)
Timeresolved particle image velocimetry (TRPIV) has been achieved
in a highspeed wind tunnel and a shock tube, providing velocity
field movies of compressible turbulence events. The requirements of
highspeed flows demand greater energy at faster pulse rates than
possible with the TRPIV systems developed for lowspeed flows. This
has been realized using a pulseburst 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 pulseburst laser
are a limited burst duration of 10.2 ms and a low duty cycle for
data acquisition. Pulseburst 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 gassolid
flow. The present work represents the first use of TRPIV in a
highspeed 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 laserbased
instrumentation techniques and highfrequency 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 adversepressuregradients
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 pressuregradient 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 wellresolved inhouse largeeddy and direct numerical
simulations as well as wind tunnel experiments.
A recurring tool in the investigation of these topics is the
diagnosticplot concept, which indicates a linear dependence between
the turbulence intensity and its mean velocity and turns out to be
useful when establishing a wellbehaved state in the outer layer of
wallbounded turbulent flows and determining the boundary layer edge
in strong PG cases or TBLs on curved surfaces. A possible analogy
between highRe ZPG TBL flows and strong APG TBLs is also considered
in light of negative wallshear 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 wallbounded 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 wallbounded turbulent flows with strong numerical
collaborations. Other active areas cover measurement technique
development/correction for highReynolds number wallbounded flows
as well as applications in internal combustion engine related flows
and various flow control strategies for separation delay and
skinfriction drag reduction. Dr. Örlü has about 50
journal publications, and a wide network with other researchers in
wallbounded turbulence research.
Experimental investigation of twophase 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 liquidgas to pure
liquidvapour twophase 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
longlived largescale microbubble laden wakes with properties
significantly altered compared with those of the outer fluid.
Techniques and results on various twophase 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, millimetrebubble break and coalescence in
turbulent shear flows and fluidstructure 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, fluidstructure interaction and hydroacoustics.
Completion: Numerical simulations of twophase 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 twophase 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. Twophase 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 twophase 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 singlephase flow research, the development of predictive
models for the twophase flow follows along three parallel paths,
namely theoretical models, laboratory experiments and numerical
simulations. There are some cases where fullscale 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 twophase flow problems heavily rely on the
employment of numerical simulations. The study of dynamics of
twophase 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 twophase
flow.
Current twophase 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 "twofluid" 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 twophase flow using both
Eulerian and Lagrangian approaches on three different twophase flow
problems, namely gravity currents, particleladen currents and
enhanced targeted drug delivery in a vascular tree.This PhD work
provides a much needed knowledge on different twophase flow
numerical modelling approaches by solving the aforementioned real
life scenarios. Specifically, the success of this PhD work would
lead to better twophase 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 longterm 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 shortcrestedness of a wave field is
investigated in terms of the threedimensional 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 nonuniformity 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 nonlinear 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 highReynolds number state. With this goal in mind, timeresolved
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 temporallyresolved 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 largescale coherent motions. Based on these findings, a
conceptual model which describes dynamic interactions of coherent features
is proposed and discussed.
Selfsustaining 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 shearinduced turbulence, where it is known that there are coherent
structures, like velocity streaks and streamwise elongated vortices, similar
to wallbounded 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 largestscale motion is restricted by
the computational domain, and it grows, breakdowns, and regenerates
quasiperiodically, reminiscent to the selfsustaining motion and bursts in
wallbounded flow. The long term simulation of HST reaches the statistically
stationary state. Direct numerical simulations (DNS) of statistically
stationary homogeneous shear turbulence (SSHST) 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
wallbounded flow. SSHST 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 selfsustaining process
(SSP) in wallbounded flow.
The speaker received a PhD in thermofluid 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, F_{0}^{1/3}, where F_{0} 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
singleinput singleoutput 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 setups 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 nearfield
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 reentrant 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 nearfield and farfield
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 wallflow 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 wallbounded
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 wallnormal 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 walllocations. 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
wallflows. 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 outofplane 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 laserbased 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 wellmatched
laser profiles. A more rigorous experimental quantification of these
behaviours has the potential to enhance the quality of PIV results.
Towards a Moodylike 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
lengthscale that varies parametrically with streamwise distance. For
Reynolds numbers based on the outer velocity and streamwise distance that
are large, use is made of a simple model of the local turbulent
meanvelocity 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 meanflow parameters can be readily
calculated. Results from this model are discussed for the
zeropressuregradient 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 wallmodeled, largeeddy
simulation (LES) of the zeropressuregradient turbulent boundary layer at
very large Reynolds numbers. Both model and LES results are consistent with
the selfpreservation arguments of Talluru et al. (2016). It is
argued that the present model/LES can be interpreted as providing the
asymptotically roughwall equivalent of a Moodylike diagram for turbulent
boundary layers in the presence of smallscale 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 largeeddy 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: vortexwave
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 zeropressuregradient 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 Reynoldsaveraged 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 nearwall
asymptotic expansion must be of the form f_{0}(y^{+})
− f_{1}(y^{+}) / U_{∞}^{+}
+ O(U_{∞}^{+})^{−2}, where f_{0}
and f_{1} 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 y_{break}^{+} =
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 / Re_{δ*}^{0.5}) with
Re_{δ*} 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 socalled "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.
Largeamplitude flapping of an invertedflag 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 clampedend, 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
freeedge, dramatically alters its dynamics. In contrast to the conventional
flag, which exhibits (smallamplitude) flutter above a critical flow speed,
the invertedflag displays largeamplitude 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
largeamplitude 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
invertedflag 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 threedimensional 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 domainscale 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/nonturbulent interface (TNTI) relative to the fluid. We find that
locally this process is dominated by smallscale diffusion which is
amplified by interfaceconvolutions 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.

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 bluffbody 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 wellstudied flows in fluid mechanics. It often serves as a
canonical flow for understanding all bluffbody 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 fluidstructure 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 lowpressure 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)

The control of nearwall turbulence by nonconventional surfaces
Ricardo GarcíaMayoral
University of Cambridge
4pm Friday 8 April 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

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)

Completion: Structure of mean dynamics and spanwise vorticity in turbulent boundary layers
Caleb MorrillWinter
University of Melbourne
3.30pm Thursday 24 March 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

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)

Highfidelity simulations of noise radiation from an elastic trailingedge
Stefan Schlanderer
University of Melbourne
4pm Friday 11 March 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

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)

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)

Coherent features in jet aeroacoustics and wallbounded turbulence
Woutijn Baars
University of Melbourne
4pm Friday 19 February 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

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)

Investigation of supercritical airfoil dynamic response due to transonic buffet
Robert Carrese
RMIT University
Transition prediction for nonaxisymmetric 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)