• Melissa Kozul
Norwegian University of Science and Technology

3.30pm Friday 3 July 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

• ## Attached eddy model revisited with quasilinear approximation*

Yongyun Hwang
Imperial College London

3.30pm Friday 13 March 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Townsend’s model of attached eddies for boundary layers is revisited with a quasi-linear approximation. The velocity field is decomposed into a mean profile and fluctuations. While the mean is obtained from the nonlinear equations, the fluctuations are modelled by replacing the nonlinear self-interaction terms with an eddy-viscosity-based turbulent diffusion and a stochastic forcing. The colour and amplitude of the stochastic forcing are then determined self-consistently by solving an optimisation problem which minimises the difference between the Reynolds shear stresses from the mean and fluctuation equations. When applied to turbulent channel flow in a range of friction Reynolds number from Reτ = 500 to Reτ = 20000, the resulting turbulence intensity profile and energy spectra exhibit exactly the same qualitative behaviour as DNS data throughout the entire wall-normal location, while reproducing the early theoretical predictions of Townsend and Perry within a controlled approximation to the Navier-Stokes equations. Finally, the proposed quasi-linear approximation suggests that the peak streamwise and spanwise turbulence intensities may deviate slightly from the logarithmic scaling with Reynolds number for Reτ > 10000.

*This is joint work with Bruno Eckhardt who sadly passed away recently.

Yongyun Hwang is a senior lecturer in the Department of Aeronautics at Imperial College London. He received his PhD in the Hydrodynamics Laboratory (LadHyX) at Ecole Polytechnique in 2010. After spending one and half years at the same institution as a post-doctoral researcher, he moved to the Department of Applied Mathematics and Theoretical Physics (DAMTP) at University of Cambridge as a Marie Curie post-doctoral research fellow to study pattern formations in active fluids in 2012. He joined Imperial College London in October 2013. His research interests are broadly defined in theoretical and computational fluid dynamics, and he specialises instabilities, coherent structures, turbulence and pattern formations in physical and biological systems.

• ## Bifurcation of periodic flows around flapping bodies

Olivier Marquet
ONERA

3.30pm Tuesday 10 March 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Two-dimensional flows induced by flapping rigid bodies may exhibit surprising dynamical behaviors that are simply obtained by unsteady numerical simulations of the fluid-solid interaction. During that talk, we will first illustrate several interesting states arising in three configurations widely investigated in the last decade: (i) the time-averaged deviation of the periodic vortex-street generated in the wake of a wing with a prescribed harmonic pitching motion, (ii) the synchronization (or not) of a spring-mounted cylinder with the vortex-shedding in its wake and (iii) the coherent or back-and-forth self-propulsion of flapping plates in an initially quiescent flow. In the second part of this talk, we will show that, for all of these cases, the occurrence of these states can be explained as bifurcations of periodic solutions of the governing equations. To that aim, I will introduce two methods allowing the numerical computation of unstable periodic solutions. The symmetry-preserving method, based on time-marching simulations, has been used to compute unstable periodic solutions with (iii) spatial or (i) spatio-temporal symmetries, while the more general harmonic balance method solve for periodic solutions in the frequency domain. Using Floquet analysis to determine the stability of those periodic solutions, we can then obtain bifurcation diagrams that I will finally use to better understand (ii) the lock-in phenomenon in vortex induced vibrations and (iii) the existence of coherent and back-and forth oscillating state for self-propelled flapping plate.

In 2003, Olivier received an engineering degree from Ecole Nationale Supérieure de Technique Avancées (ENSTA, France) and a master degree in mechanical engineering, speciality in fluid mechanics, from University Pierre & Marie Curie (UPMC, France). In October 2003, he received a PhD grant from the Direction Générale de l’Armement (DGA) and started a doctoral thesis at the Fundamental and Experimental Aerodynamics Department (DAFE) of ONERA. In December 2007, he received a doctoral degree from the University of Poitiers for his work on the Global stability and control of recirculating flows. In January 2008, he obtained a Junior Research Fellowship from DGA and started a one-year postdoctoral project at the Universität der Bundeswehr in Munich (Germany). In 2009, he came back to France for a one-year post-doctoral project on the optimal forcing of boundary layer instabilities, at Laboratoire d'Hydrodynamique (LadHyx) from Ecole Polytechnique and ONERA-DAFE. In January 2010, he got a permanent position as research engineer within the Fluid Mechanics Unit (MFLU) of ONERA-DAFE. In March 2015, he received a Starting Grant from the Eurpeoan Research Council for the project AEROFLEX, AEROelastic instabilities and control of FLEXible structures. In 2016, he became Maitre de Recherche at ONERA and member of the scientific council for the Energetic and Fluid Mechanics branch. Since January 2018, he is a senior research scientist in the Metrology, Assimilation and Flow Physics Unit (MAPE for Metrologie, Assimilation et Physique des Ecoulements) of the ONERA Aerodynamics, Aeroelasticity and Acoustics Department (DAAA).

• ## Three-dimensional boundary layers with short spanwise scales

Peter Duck
University of Manchester

4.00pm Friday 6 March 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

We consider three-dimensional boundary-layer flows, where the spanwise scale is comparable to that of the boundary-layer thickness. To place this three-dimensional formulation into a specific context, we consider a semi-infinite flat plate aligned with an oncoming incompressible, uniform flow of speed U*. An arbitrary choice of reference length scale, L*, allows for a non-dimensional Cartesian coordinate system (L* x,L*y,L*z) aligned with the leading edge of the plate at x=0, such that y=0, x>0 defines the plate surface. To capture short spanwise scales typical of streaks we rescale in the (y,z) plane according to (Y,Z) = Re1/2 (y,z). Here Re=U* L*ν* (for kinematic viscosity ν*) is a global Reynolds number based on the chosen length scale. The corresponding high Reynolds number flow field (assumed to be steady) is

$u = \hat U(x,Y,Z,t) + \cdots\,,~(v,w) = Re^{-1/2} ( \hat V(x,Y,Z,t), \hat W(x,Y,Z,t) ) + \cdots\,,$

with pressure

$p = Re^{-1/2} \hat p(x) + Re^{-1} \hat P(x,Y,Z,t) + \cdots\,.$

For large Reynolds number the solution is therefore governed by

$\hat U_t+ \hat U \hat U_x + \hat V \hat U_Y + \hat W \hat U_Z = \hat U_{YY}+ \hat U_{ZZ},$

$\hat V_t + \hat U \hat V_x + \hat V \hat V_Y + \hat W \hat V_Z = - \hat P_Y + \hat V_{YY}+\hat V_{ZZ},$

$\hat W_t + \hat U \hat W_x + \hat V \hat W_Y + \hat W \hat W_Z = - \hat P_Z + \hat W_{YY}+ \hat W_{ZZ},$

$\hat U_x + \hat V_Y + \hat W_Z = 0.$

This system is often referred to as the boundary-region equations.

This system encompasses much of the full flow physics, and is applicable to a wide variety of flow configurations, including corner boundary layers, spanwise-periodically disturbed flows with links to transient growth and streaks. We first consider steady three-dimensional states driven by a finite-width slot aligned with the flow direction and self-similar in their downstream development. The classical two-dimensional states are known to only exist up to a critical ('blow off') injection amplitude, but the three-dimensional solutions here appear possible for any injection velocity. We then go on to consider both the formation and stability of isolated streak structures embedded in a Blasius boundary layer, triggered by injection of fluid through the surface of the plate. Finally we consider the far downstream behaviour of (small amplitude) unsteady disturbances to Blasius boundary layers. We discuss the two disparate structures that have been proposed for two-dimensional (eigen-) disturbances, the first due to Lam & Rott (1960) and Ackerberg & Phillips (1972) and the second due to Brown & Stewartson (1973).

Peter Duck is a Professor of Applied Mathematics at the University of Manchester. He received his BSc in Aeronautics and his Ph.D. from the University of Southampton and went on to do post-docs at Imperial College London in Mathematics and Ohio State University in Aeronautics. In 1979, he moved to the University of Manchester where he has served as the Head of Department and School of Mathematics. His research interests in fluid mechanics include asymptotic methods, boundary-layer flows, separated flows, and linear and nonlinear instabilities. He is currently the Executive Editor of the Quarterly Journal of Mechanics and Applied Mathematics and an Associate Editor of Theoretical and Computational Fluid Dynamics. Additionally, he has supervised over 40 research students and authored over 140 scientific articles.

• ## Recent developments in zonal Hybrid RANS LES methods for industrial applications

Alistair Revell
University of Manchester

3.30pm Friday 28 February 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

In my talk I will present an overview of recent developments in turbulence modelling and simulation where scale-resolution is sought at reduced cost. Hybrid RANS-LES methods are first introduced and discussed in general, and the importance of the RANS model is highlighted. In this context I will show that zonal methods are a versatile tool, providing efficient approximation of fluctuations in order to move from time-averaged to instantaneous treatment. Code-code coupling approaches are presented, deploying multiple instances to simultaneously solve separate RANS and LES domains, interlinked via volume source terms. I will then present details of a similar approach which instead uses the lattice Boltzmann method accelerated on GPU devices as the time-resolving component, coupled to a RANS finite volume method solver running on CPU; with some reflections on the opportunities this provides.

Alistair graduated from UMIST with an MEng degree in Aerospace Engineering with French, including time at ENSMA, Poitiers. He was again based in Manchester for his PhD in Turbulence Modelling, including a year at IMFT, Toulouse and shorter placements at Electricité de France (EdF), Paris and Stanford CTR. He became a Lecturer at Manchester in 2007, initially focussed on the development of Code_Saturne in collaboration with EdF. In 2011 he undertook a research sabbatical in Madrid to work on fluid-structure interaction and the lattice Boltzmann method. In 2017 he became Reader and Deputy Head of Department of Mechanical, Aerospace & Civil Engineering and is also Head of Social Responsibility. He leads a research group working on the development of CFD methods for turbulent flow and fluid-structure interaction.

• ## Calculation of the mean velocity profile for strongly turbulent Taylor–Couette flow and arbitrary radius ratios

Pieter Berghout
University of Twente

3.30pm Friday 21 February 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Taylor–Couette (TC) flow is the shear-driven flow between two coaxial independently rotating cylinders. In recent years, high-fidelity simulations and experiments revealed the shape of the streamwise and angular velocity profiles up to very high Reynolds numbers. However, due to curvature effects, so far no theory has been able to correctly describe the turbulent streamwise velocity profile for all radius ratios, as the classical Prandtl–von Kármán logarithmic law for turbulent boundary layers (BLs) over a flat surface at most fits in a limited spatial region.

Here we address this deficiency by applying the idea of a Monin–Obukhov curvature length to turbulent TC flow. This length separates the flow regions where the production of turbulent kinetic energy is governed either by pure shear from that where it acts in combination with the curvature of the streamlines. We demonstrate that for all Reynolds numbers and radius ratios, the mean streamwise and angular velocity profiles collapse according to this separation. We then derive the functional form of the velocity profile. Finally, we match the newly derived angular velocity profile with the constant angular momentum profile at the height of the boundary layer, to obtain the dependence of the torque on the Reynolds number, or, in other words, of the generalized Nusselt number (i.e., the dimensionless angular velocity transport) on the Taylor number.

Pieter graduated as a Chemical Engineer from Delft University of Technology in 2015. His thesis was on the Lattice Boltzmann modelling of surfactant laden droplets, and continued this research for another year as a research assistant at the University of Limerick, Ireland. In 2017, he started his PhD at the Physics of Fluids group at the University of Twente under Detlef Lohse, working on various topics in turbulent Taylor-Couette flow.

• ## The effect of heat transfer on turbine performance

Lachlan Jardine
Whittle Lab, University of Cambridge

3.30pm Friday 7 February 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

For over 60 years, gas turbines have bled air from the compressor to cool blades in the high-pressure turbine. The cooling air is used to protect these turbine blades, allowing them to operate at temperatures several hundred degrees above their melting point. It is therefore surprising that little is understood about the effect of heat transfer on turbine efficiency. There is not even a consensus on how to define the efficiency of a cooled turbine. This talk seeks to demonstrate a thermodynamic method capable of linking different levels of design, rigorously defining turbine performance and agreeing with industrial experience.

Lachlan has recently submitted his PhD thesis at the Whittle Laboratory, University of Cambridge, which investigates the impact of cooling on gas turbine performance. He has successfully obtained a Knowledge Transfer Fellowship, in partnership with Rolls-Royce, to continue developing this research. More broadly, Lachlan is particularly interested in the fields of heat transfer, computational fluid dynamics and turbulence.

## Vorticity fluxes: A tool for three-dimensional secondary flows in turbulent Shear flows

Hassan Nagib
Illinois Institute of Technology

3.30pm Thursday 6 February 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

• ## Nonlinear optimisation of transition in pipe flow

Ashley Willis
University of Sheffield

3.00pm Tuesday 4 February 2020
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Turbulence and laminar flow can coexist at the same flow rate in pipe-, Couette- and channel-flows. Starting from each of the two states, two nonlinear optimisation problems can be asked: "What is the minimal disturbance to laminar flow that causes transition to turbulence?" and "What is the minimal (body) force that can 'destabilise' turbulence towards relaminarisation?". In particular, this latter problem is motivated by surprising experiments showing that a partial blockage in a pipe can actually lead to relaminarisation, rather than just stirring up more turbulence (Kühnen et al. 2018, Nature Physics 14, 386). The two questions can be formulated as similar nonlinear variational problems, in principle. Several issues arise in practice, but optimal perturbations and forces of consistent structure can nevertheless be determined.

Ashley Willis completed his PhD at Newcastle University, U.K, on flows related to the magnetic stability of accretion discs. He studied the geodynamo in Leeds before moving to Bristol to work on fundamental fluid mechanics. He went on to a Marie Curie fellowship at LadHyX, Ecole Polytechnique near Paris, before settling in Sheffield.

• ## Wall-bounded stratified turbulence

Francesco Zonta
TU Wien

3.30pm Tuesday 17 December 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

In this talk, I will focus on the problem of stratified flows in wall-bounded turbulence. In the first part of the talk, I will consider the case of thermally-stratified flows. The interaction between turbulence and thermal stratification induces remarkable modifications on the flow field, which in turn influences the overall transfer rates of mass, momentum and heat. The discussion will spin around recent results obtained by a systematic campaign of Direct Numerical Simulations of stratified turbulence at large Reynolds number. In the second part of the talk, I will consider the case of viscosity-stratified flows. I will focus on a lubricated channel (i.e. a flow configuration in which an interface separates a thin layer of a less-viscous fluid from a main layer of a more-viscous fluid flowing inside a plane channel), and I will discuss the influence of viscosity and surface tension on the overall friction (drag reduction mechanism).

Dr. Francesco Zonta graduated in Mechanical Engineering in 2006 at the University of Udine, where he also completed his PhD in 2010. From 2010 to 2016 he has been Research Assistant at the University of Udine and at the University of Torino. In 2014, he has been invited scholar at the University Pierre et Marie Curie (UPMC, Paris). Since 2016, he is Senior University assistant at the Institute of Fluid Mechanics and Heat Transfer of the Vienna University of Technology. His research focuses on turbulence, heat transfer, multiphase flows and computational fluid dynamics. He has obtained a number of grants for HPC (High Performance Computing) applications, and he has been the recipient of "Ermanno Grinzato" prize awarded by AIPT (2013).

• ## Vortex structure over cubical block array

Naoki Ikegaya
Kyushu University

3.30pm Tuesday 10 December 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

The momentum and scalar transports from an urban surface into an atmosphere is one of the important factors to determine environment in the urban area. The geometric dependency of macroscopic aerodynamic parameters such as the transfer coefficients for momentum and scalar has been revealed by a series of wind-tunnel experiments. However, it is not well known that the features of locally generated turbulent flow structures due to the ejection event, strong upward transport of low-speed momentum fluid, and the sweep event, strong downward transport of high-speed momentum fluid for the urban-like boundary layer. Therefore, we performed numerical simulation using Large-eddy simulation model over urban-like surfaces consisted of cubical blocks. The quadrant analysis for instantaneous flow field is conducted to investigate the contribution of ejection or sweep to the total momentum transport over cubical arrays. In addition, the conditional averaged flow fields show that the ejection or sweep event can be generated by the pair-vortex probably corresponding to the leg structures of hair-pin vortex, resulting in the strong upward or downward flow.

Dr Naoki Ikegaya is an Assistant Professor in Faculty of Engineering Sciences, Kyushu University, Japan. He received his Doctorate degree of Engineering from Kyushu University in 2011. His major is architectural environmental engineering and wind engineering by means of both wind-tunnel experiment and computational fluid dynamics approach. He focuses on transport phenomena occurring in the turbulent urban boundary layer where various rigid buildings work as roughness to generate complex and non-uniform turbulent flows within the urban canopy layer. He is currently a Visiting Scientists in Ocean and Atmosphere, Commonwealth Scientific and Industrial Research Organisation (CSIRO) to work with Prof. J.J. Finnigan on the turbulent statistics scaling over various vegetation and urban canopies.

• ## Drag-reduction using compliant coatings: Learning from the Dolphin?

Tony Lucey
Curtin University

3.30pm Friday 6 December 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Reducing the drag, and thus the propulsive power requirement, of any vehicle is highly desirable in an age of environmental concerns and inexorably increasing fuel costs. Nature has been 'working' on such challenges for millions of years through the process of evolution; the 'design' of the dolphin is an outstanding example of its success in marine locomotion. One facet of its hydrodynamic optimisation appears to arise from the structure of its skin that dynamically interacts with the flow of water past it when the dolphin is in motion.

This presentation will tell the story of research on compliant coatings, an artificial rubber-based equivalent of the dolphin's skin, that attempt to confer similar hydrodynamic advantages when applied to an otherwise rigid wetted surface. In particular it will focus on the research evidence that compliant coatings are able to postpone the transition from laminar to turbulent flow in the boundary layer, thereby reducing skin-friction drag. In fact, there is, at least theoretically, the possibility of postponing the onset of turbulence indefinitely to reach the 'Holy Grail' of low-drag design. There is also evidence that compliant coatings can reduce turbulent skin-friction although the underlying mechanisms for this are not yet well understood. More broadly, the presentation will serve as a case study of the sometimes tortuous path of research from scientific observation to understanding of fundamental physical phenomena and from there to future technologies.

Tony Lucey is a John Curtin Distinguished Professor, twice former Dean of Engineering (2005–2008, 2015–2018), and former (2009–2019) Head of the School of Civil and Mechanical Engineering at Curtin University. He took his Bachelor and PhD degrees at the Universities of Cambridge and Exeter in the UK. He has held positions at the Universities of Exeter and Warwick in the UK and the Asian University of Science and Technology in Thailand. He gained industrial experience as an aerodynamicist at British Aerospace PLC in the UK. He is recognised for his fundamental research in fluid-structure interaction and its applications in engineering and biomechanics. He also publishes in the areas of engineering education and appropriate technology. His career has been punctuated by spells working in, or for, developing countries. He is active in the peak professional body Engineers Australia (EA): this has included being the 2010 WA Division President and regularly chairing EA panels for the accreditation of Engineering degrees at Australian universities (including Melbourne!). He has served on the ARC College (2012–2014) and its Selection Advisory Committee (2019). He was Secretary of the Australasian Fluid Mechanics Society from its inception in 2009 and in 2019 became President of the Society.

• ## Barnacle fouling and its effect on near-wall turbulence

Angela Busse
University of Glasgow

3.30pm Wednesday 4 December 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Marine biofouling has impacted seafaring since ancient times by decreasing the maximum range and speed of watercraft. As marine organisms accumulate on a ship, the skin-friction drag of the hull rises significantly, leading to higher fuel burn and associated emissions. The form of biofouling with the most severe impact on the shipping industry is calcareous macrofouling which is caused by organisms protected by a calcareous outer shell, such as barnacles, tubeworms, and mussels.

This presentation will focus on the impact of barnacle-type roughness on wall-bounded turbulence. The rough surfaces under consideration have been generated with an algorithm that mimics the settlement behaviour of barnacles. Direct numerical simulations are used to quantify the effects of different topographical parameters such surface coverage and clustering on near-wall turbulence statistics.

Barnacle-type roughness can be interpreted as an 'hybrid' form of roughness that combines both features of irregular multi-scale roughness and traditional regular rough surfaces built from roughness elements. It therefore serves as an interesting test case for the commonalities and dissimilarities of the fluid dynamic effects of regular versus irregular forms of surface roughness.

Dr Angela Busse is a lecturer in the James Watt School of Engineering at the University of Glasgow. Her main research area is the effect of rough and superhydrophobic surfaces on wall-bounded turbulence. Her further research interests include Lagrangian statistics of turbulence, magnetohydrodynamic turbulence, flows past bluff bodies, and the aerodynamics of plants.

• ## Studies on complex flows with tomographic PIV

Qi Gao
Zhejiang University

3.30pm Friday 18 October 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Tomographic particle image velocimetry (TPIV) proposed by Elsinga et al. (2006) has become a powerful experimental technique to measure a three-dimensional three-components (3D3C) velocity field. With high-frequent sampling, time-resolved TPIV can further achieve pressure reconstruction at the same time with volumetric velocity measurement. Therefore, this technique is widely used for studying complex flows. In this talk, several classical flows based on TPIV measurement will be briefly presented. A flow passing a hemisphere in laminar boundary layer is highly associated with transition. With time-resolved TPIV, both velocity and pressure fields are measured to see the revolution of the induced standing vortices and hairpin vortices. For a turbulent boundary layer (TBL) flow, dominant vortex structures in near-wall region are statistically investigated. Methods of linear stochastic estimation (LSE), proper orthogonal decomposition (POD) and pre-multiplied energy spectra are utilized for studying coherent flow structures regarding scales, amplitude and frequency modulation effects on the inner–outer interactions of TBL. A point-swirl model is being developed for eddy modeling. There are several ongoing projects on TPIV measurements of live fish swimming, critical cavitation of tip vortex, laser induced cavitation, homogeneous isotropic turbulence (HIT) generated with a turbulent box and breakdown of leading vortices of a delta wing. Meanwhile, a series of post-processing methods are proposed for better noised reduction, error elimination and missing data fixing based on physical constraints from continuity, momentum and irrotational equations.

Dr Qi Gao received his bachelor degree from Zhejiang University in 2001, his master degree from Tsinghua University in 2005, and his Ph.D. from the University of Minnesota in 2011. He joined the Beijing University of Aeronautics and Astronautics as an assistant professor in 2011, and was promoted to associate professor in 2013. He moved to Zhejiang University in 2018. Currently, he is an associate professor at the School of Aeronautics and Astronautics, Zhejiang University, China and serves as the Director of Laboratory of Fluid Mechanics at the Institute of Fluid Engineering. Dr. Gao's research is broadly in the area of experimental fluid mechanics. Current projects are focused on developing techniques of volumetric velocimetry and their applications. Studies on turbulent boundary layers, cardiovascular flows, compressible flows and flow control are areas of high interest. He has published about 30 research articles and applied for over 40 patents (10 have been certified). Dr. Gao received the Chinese National Award of Technology Invention (second class) in 2018.

• ## 3D Lagrangian particle tracking with Shake-The-Box

Peter Manovski
University of Melbourne

3.30pm Friday 4 October 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

This talk will focus on two test campaigns conducted at the German Aerospace Centre (DLR) using the new Lagrangian Particle Tracking algorithm Shake-The-Box (STB). Firstly, time-resolved STB was applied to a low speed impinging jet flow. Helium-filled soap bubbles were used as tracer particles, illuminated with pulsed LED arrays and captured with six high speed cameras. A large measurement volume (54 L), captured up to 180,000 particle tracks for a jet velocity of 4 m/s. Reconstructed instantaneous volumetric pressure fields were obtained and validated against microphone recordings at the wall. The second test used multi-pulse STB to measure the subsonic jet flow at Mach 0.85. Using two imaging systems each with four cameras and four lasers, up to 50,000 tracks of four-pulse sequences were captured, enabling high resolution instantaneous and 3D flow fields of velocity and material acceleration. For the first time, this revealed 3D acceleration and fluctuation fields, as well as PDF statistics. Bin-averaging of the particle tracks provided sub-pixel (0.75 px) resolution statistical quantities that were able to resolve the extremely steep velocity gradients in the jet shear layer. In the final component of the talk I will provide a brief outlook of my intended PhD research studies at The University of Melbourne.

Peter Manovski graduated from Monash University in 2005 completing a double degree in Bachelor of Engineering (Mechanical) and Bachelor of Technology (Aerospace) with First Class Honours. The following year he obtained employment with Defence Science and Technology (DST) Group Melbourne. Working in the field of Experimental Aerodynamics for over 14 years, he has gained significant knowledge and experience in both low speed and transonic wind tunnel test techniques. He leads a small team working in the DST wind tunnels that is responsible for planning, conducting, analysing and reporting of aerodynamic experiments in support of Defence S&T programs and fundamental research initiatives across the Aerospace and Maritime domains. In 2016, he was awarded a DST International Fellowship and was posted at the German Aerospace Centre (DLR) for 14 months.

Recently he commenced a work-based PhD (part-time) at The University of Melbourne with the aim of characterising the acoustic performance of UAS with the application of synchronised volumetric flow field and acoustic measurements.

• ## Friction and fluctuations in transitional pipe flow

Rory Cerbus
Okinawa Institute of Science and Technology

3.30pm Tuesday 24 September 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Pipe flow is laminar at low flow velocities and turbulent at high flow velocities. At intermediate velocities there is a transition wherein plugs of laminar flow alternate along the pipe with "flashes" of a type of fluctuating, non-laminar flow which continue to be the object of intense study. Here we address two properties of flashes: friction and fluctuations. In the 19th century, Osborne Reynolds, who first reported flashes, sought to connect them with quantitative "laws of resistance" whereby the fluid friction is determined as a function of the Reynolds number. While he succeeded for laminar and turbulent flows, the laws for transitional flows eluded him and remain unknown to this day. In seemingly unrelated work, A.N. Kolmogorov predicted that all turbulent flows are the same at small scales: the property of 'small-scale universality'. Based on the restrictive assumptions invoked by Kolmogorov to demonstrate this universality, it is widely thought that only idealized turbulent flows conform to this framework. Using experiments and simulations that span a wide range of Reynolds number and by properly distinguishing between flashes and laminar plugs in the transitional regime, we uncover the law of resistance for flashes and demonstrate for the first time that small-scale universality holds even in low Reynolds number, inhomogeneous, unsteady transitional pipe flow.

Rory is a Staff Scientist in Pinaki Chakraborty's Fluid Mechanics Unit at the Okinawa Institute of Science and Technology (OIST) in Okinawa, Japan. Rory received his Ph.D. in Physics in 2014 from the University of Pittsburgh experimentally studying two-dimensional turbulence under the direction of Walter Goldburg. At OIST, Rory has continued working on two-dimensional turbulence but mainly focuses on experiments and simulations of transitional pipe flow. In January 2020, Rory will move to the Université de Bordeaux in France to work with Hamid Kellay on granular flows under a Marie Skłodowska-Curie Fellowship.

• ## Replacing the heart with a mechanical pump

Shaun Gregory
Monash University

3.30pm Friday 20 September 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Heart failure is an expanding global health issue while the gold-standard treatment, heart transplant, is limited by low organ donation numbers. Mechanical solutions to bridge patients to transplant or as a destination therapy come in the form of rotary blood pumps which use magnetically suspended and rotated impellers to take over the native heart's blood-pumping function. These devices are prone to complications such as bleeding, clotting, infection and an inability to change performance based on changes in patient activity. Collaborative research between Monash University, the Alfred Hospital, and the Baker Heart and Diabetes Institute aims to solve these issues by forming a close collaboration between engineers, biological scientists, clinicians and patients. This presentation will summarise the key research projects underway through this collaboration including the development of new devices, evaluation of blood flow dynamics, reducing infection through electro-writing, physiological control systems, and more.

Dr Shaun Gregory is a senior lecturer in the department of Mechanical and Aerospace Engineering at Monash University, a Heart Foundation Future Leader Fellow, and an Honorary Research Fellow in the Baker Heart and Diabetes Institute. He holds a PhD in medical engineering from Queensland University of Technology, and has completed research fellowships at the University of Queensland and Griffith University. Shaun's research interests centre around cardiovascular engineering, with a specific focus on the development and evaluation of mechanical circulatory and respiratory support systems (artificial hearts and lungs). Shaun directs a cardiovascular engineering research laboratory in the Baker Heart and Diabetes Institute where engineers, clinicians and biological scientists work side-by-side at the bench to develop novel solutions to clinically-relevant problems.

• ## Global linear stability theory in aerospace applications

Vassilios Theofilis
University of Liverpool

3pm Wednesday 18 September 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Global linear stability theory is the natural extension of the classic local analysis in flows with multiple inhomogeneous spatial directions. The lecture will provide an overview of highlights of laminar-turbulent transition research based on linear theory, from its early development in Göttingen by Prandtl himself, Tollmien, Schlichting, Görtler and others, up to the present-day theoretical developments, natural laminar flow wing wind-tunnel experiments and flight tests. Subsequently, successes of global linear theory will be highlighted in a number of external and internal aerospace applications in the incompressible limit, including the swept leading edge boundary layer at the windward face of an aircraft wing; global modes (and stall-cell formation) on spanwise homogeneous and three-dimensional wings; centrifugal instabilities in two- and three-dimensional open cavities and in rotating cavities of the High Pressure Turbine of an aircraft engine. In a supersonic boundary layer, PSE-3D transition prediction in the wake of an isolated roughness element will be discussed, while instability and transition prediction in two hypersonic flows will be highlighted: an elliptic cone modelling Ma=7 flight of the HIFiRE-5 research vehicle and shock/laminar boundary layer interaction on a double cone at Ma=15. It will be argued that improved understanding of flow instability in geometrically complex configurations, especially in the high speed regime, is expected to deliver physics-based flow control methodologies that will aid the development of next-generation flight vehicles in the first half of this century.

• ## Loss analysis of axial compressor cascades

Jake Leggett
University of Melbourne

3.30pm Friday 13 September 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

The prediction of an axial compressor's loss early on in the design phase is a valuable and important part of the design process. The work presented here focuses on assessing the accuracy of current prediction methods, Reynolds Averaged Navier ndash;Stokes (RANS), compared with highly accurate Large Eddy Simulations (LES). The simulations were performed at the challenging running conditions of engine relevant Mach (0.67) and Reynolds (300,000) numbers. The work looks at the effects of off-design incidence and the influence of different free-stream disturbances on loss prediction. From the highly accurate data sets produced by the LES the work is able to show how loss attribution varies under different conditions, and goes on to compare how well RANS captures these changes. It was found that overall loss trends are captured well by RANS but substantial differences exist when comparing individual loss sources, which are shown to vary significantly under different running conditions. The investigation into loss attribution is performed using the Denton (1993) loss breakdown as well as a novel application of the Miller (2013) mechanical work potential. In addition to the discovery of the variation in the sources of loss, the comparison between the loss analyses highlighted some of the limitations of the Denton loss breakdown, which was shown to have increasing error under large off-design incidence or in the presence of discrete disturbances. From the comparison of the loss breakdown analyses and LES and RANS flow field results, new insight into the characteristics, limitations and short comings of current modeling techniques have been found. The variation in the sources of loss under different running conditions was also discovered.

Jake completed his undergraduate at the University of Manchester after which he went on to do his masters at Imperial college London in computational fluid dynamics. He then moved to the University of Southampton to complete his PhD, focusing on loss predictions of axial compressor cascades using CFD. He is now currently a research fellow at the University of Melbourne, continuing his work on axial compressors, and focusing on numerical model development and improved loss prediction techniques of turbo machinery flows.

• ## Completion: Compressible turbulent wakes in constant area pressure gradients: simulation and modelling

Chitrarth Lav
University of Melbourne

3.30pm Friday 23 August 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Improving turbomachinery efficiency today is directly related to quantifying and reducing the various sources of losses. Of these, the wake mixing loss, resulting from wakes produced by the blade trailing edge, is of prime interest. These wakes, when developing spatially through the periodic constant area passage in the stator-rotor row, are exposed to pressure gradients which can impact the wake evolution and consequently the wake mixing loss. Since a study on the effect of the pressure gradient in isolation is not possible in an actual turbomachine stage, a canonical case study, of a statistically two-dimensional turbulent wake, is proposed to understand and predict the underlying flow physics arising from the presence of pressure gradients. Through the use of compressible high-fidelity simulations, the relevant flow quantities are scrutinised to explain the effect of the pressure gradients. While the understanding developed through the high-fidelity data is invaluable, prediction of these flows is still a challenge with the existing URANS, due to the poor underlying turbulence closure. Thus, in the next stage, the prediction of the wake flow using URANS is improved by developing a new closure, obtained using the high-fidelity data of the zero pressure gradient (ZPG) wake and a symbolic machine-learning algorithm. The results from the implemented closure show an error of less than 1% with the calculation being 400 times cheaper than the DNS. The developed closure is also evaluated on 6 additional cases: ZPG wakes at different Reynolds numbers and wakes in the presence of pressure gradients, to test if the closure is re-usable and robust to changing flow conditions, with promising results. Thus, the results from the study undertaken, both from a simulative and modelling standpoint, can serve as a guide in predicting and minimising the loss produced by wake mixing.

Chitrarth's supervisors are Richard Sandberg and Jimmy Philip.

• ## Reducing aerofoil–turbulence interaction noise with bio-inspired designs

Lorna Ayton
University of Cambridge

3.30pm Friday 16 August 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

A dominant source of aeroengine noise arises when the unsteady wakes shed from rotors interact with downstream stators. This so-called leading-edge noise cannot be eliminated, but it can be reduced. By altering the spanwise geometry of the leading edge of an airfoil it is known through experimental testing that leading-edge noise can be significantly reduced over broadband frequencies. In recent years, a multitude of different shapes have been tested and all are seen to have benefits for different frequency ranges, which may be ideal for the reduction of tonal noise, but the question remains; which design is optimal for broadband noise reduction? A similar unavoidable source of noise occurs when the turbulent boundary layer over an aerofoil scatters off the sharp trailing edge, in so-called trailing-edge noise. Similar variations to the spanwise geometry are effective in reducing this noise, but also alterations to the porosity or flexibility of the trailing edge have been seen to be efficient, however again no predictive tool for the optimum adaptation has been developed. This talk will present a range of theoretical models for different aerofoil adaptations which are known to reduce broadband turbulence interaction noise, and will illustrate how they may be used as a stepping stone towards determining optimally quiet designs.

Lorna completed her PhD under the supervision of Nigel Peake in 2014 in the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge. From there she undertook a 3-year Junior Research Fellowship funded by Sidney Sussex College, and now is funded by a 5-year EPSRC Early Career Fellowship held in DAMTP. Her research focusses on developing theoretical models for aeroacoustics, in particular aerofoil-turbulence interaction, and on advancing fundamental mathematical methods for application to acoustic scattering problems.

• ## Population balance equation for turbulent polydisperse flows

Fatemeh Salehi
Macquarie University

3.30pm Friday 9 August 2019
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

The transport of polydispersed droplets and solid particles in turbulent flows is relevant to a wide range of applications such as particle dispersion in the atmosphere, fire suppression systems and liquid spray fuel injection in diesel engines and gas turbines. The dynamics of droplets and particles transported by a turbulent flow involves a complex series of inter-related phenomena including dispersion, surface growth or shrinkage, breakage, agglomeration and nucleation. In this talk, Dr Salehi will present an effective model based on the probability density function (PDF) form of the population balance equation (PBE) for polysized and polyshaped droplets and solid particles in turbulent flows. A key novelty of this method lies in the inclusion of an explicit consideration of the inertial effects and the shape of particles in the PDF-PBE formulation.

• ## Adjoint-based optimal flow control and invariant solutions in compressible 2D cavity flows

Javier Otero
University of Melbourne

4pm Friday 12 May 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

The advances in the understanding of compressible flows challenge researchers to tackle more ambitious problems that surpass human intuition. Hence, it becomes necessary to rely on methods that give an insight into the underlying physical mechanisms that govern these complex flows to perform non-trivial tasks such as flow control. To this end, an adjoint-based optimal flow control framework for compressible flows has been appended to an existing in-house DNS code (HiPSTAR). In particular, we focus our efforts on a 2D cavity flow at Re=5000, where we aim to reduce noise levels at the sensor location, by either reducing the overall sound radiation or altering the sound directivity. In addition, with minor coding effort, this framework is extended to permit the computation of both (stable and unstable) exact steady and periodic flow solutions in compressible flows over complex geometries. Thus, we present the families of exact periodic and steady solutions across Mach number, using the same 2D cavity flow setup with a lower Reynolds number (Re=2000). These two families of flow solutions are found to meet at the quasi-incompressible flow regime, where a stability analysis on both periodic and equilibrium solutions shows that they form a subcritical Hopf bifurcation

Javier did his undergraduate in Aerospace Engineering at the Technical University of Madrid (UPM), Spain (2008–2012); an MSc in Computational Fluid Dynamics at Cranfield University, UK (2012–2013); and PhD in development and application of an adjoint-based optimal flow control framework for compressible DNS at Southampton University, UK (2013–2017). He is now a postdoc working with Prof Richard Sandberg.

• ## Shock driven instabilities in two-fluid plasmas

Vincent Wheatley
University of Queensland

4pm Friday 28 April 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

In inertial confinement fusion (ICF) experiments, a capsule filled with fuel is imploded by shock waves generated by laser-driven ablation. The goal is to ignite a fusion burn at the centre of the implosion, and have that burn propagate through and consume the inertially confined fuel. Hydrodynamic instabilities cause mixing between the capsule material and the fuel, which is highly detrimental to the propagation of a fusion burn. One of the key hydrodynamic instabilities in ICF is the Richtmyer-Meshkov instability (RMI). This occurs when a shock interacts with a perturbed density interface, such as the interface between the capsule and the fuel. In ICF and astrophysical applications, the RMI typically occurs in plasmas. Here, we study the RMI in the context of the ideal two-fluid, ion-electron, continuum equations. These couple a separate set of conservation equations for each species to the full Maxwell equations for the evolution of the electromagnetic fields. We focus on cases with and without an imposed magnetic fields and with Debye lengths ranging from a thousandth to a tenth of the interface perturbation wavelength. For all cases investigated, the behaviour of the flow is substantially different from that predicted by the Euler or ideal magnetohydrodynamics equations. Electric fields generated by charge separation cause interface oscillations, particularly in the electrons, that drive a secondary high-wavenumber instability. Consequently, the density interface is substantially more unstable than predicted by the Euler equations for all cases investigated. Self-generated magnetic fields are predicted within our simulations, but their orientation is such that they do not dampen the RMI. In ideal magnetohydrodynamics (MHD), it has been shown that in the presence of such a seed magnetic field, the growth of the RMI is suppressed by the transport of vorticity from the interface by MHD shocks. Our two-fluid plasma simulations reveal that while the RMI is suppressed in the presence of the seed field, the suppression mechanism varies depending on the plasma length-scales. Two-fluid plasma RMI simulations also reveal that the secondary, high-wavenumber, electron-driven interface instability is not suppressed by the presence of the seed field.

Dr Vincent Wheatley is a senior lecturer in the Centre for Hypersonics within the School of Mechanical and Mining Engineering at the University of Queensland. He obtained his PhD in Aeronautics from the California Institute of Technology in 2005. He also earned an MEngSc (Mechanical) and a BE (Mechanical and Space) from the University of Queensland (UQ). After completing his PhD in the US, Dr Wheatley spent two years as post-doctoral fellow at ETH Zurich. He was then a Lecturer in Aerospace Engineering at the University of Adelaide before taking up his position at UQ in 2009.

• ## Non-laminar solutions for grooved Couette flow

University of Melbourne

4pm Friday 21 April 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

The dynamical systems approach to turbulence has gained a lot of attention since the turn of the century. A large set of exact, symmetrical solutions of the Navier-Stokes equations have been found for canonical wall-bounded flows such as Couette, channel, and pipe flows at low Reynolds numbers (~ 400). The defining characteristic of these solutions is the vortex-streak structure that is known to play a crucial role in sustaining near-wall turbulence. In state-space, some of these solutions lie in the region that is densely visited by turbulence, while some others resemble the laminar solution and regulate laminar-turbulent transition. These solutions, along with their connections in state-space, form a skeleton for trajectories of turbulent flow. In addition to providing a description of turbulence dynamics, this approach also produces an equation-based, low-rank basis for use in flow control.

This vision of turbulence has not been extended to rough-walled flows despite their practical significance. We have taken the first steps in this direction by computing exact invariant solutions for plane Couette flow with (longitudinal) grooved walls, through continuation of known solutions for smooth-walled flows using a simple domain transformation method. We find that the principal role of such grooves is to localize the vortex-streak structure near the wall, as well as to reduce the bulk energy density while increasing the dissipation rate. Similar localization of the structure is considered to produce drag reduction (~ 10%) in riblet-mounted boundary layers. While these results are fairly primitive, especially due to the low Reynolds numbers involved, we believe that further efforts in this direction can help in optimizing riblet geometries for drag reduction, and provide insight on the influence of surface-roughness on the near-wall flow.

Sabarish Vadarevu is a research fellow in the fluids group at the University of Melbourne. He worked on his PhD (awaiting completion) in Aerospace Engineering at the University of Southampton, on computing exact invariant solutions in grooved plane shear flows. Prior to that, he obtained his Bachelors and Masters degrees from the Indian Institute of Technology-Madras, with his Masters thesis involving a stability analysis of partially premixed flames in laminar mixing layers. His current research is focused on linear modelling and control of wall-bounded turbulence.

Jake Leggett
University of Southampton

4pm Tuesday 11 April 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

The work focuses on the prediction of loss in axial compressors. The majority of modern design methods use cheaper more accessible models, such as RANS, to predict flow performance. While these methods are reliable and easier to use they do not always provide the accuracy needed. The aim of the work presented is to improve our understanding of how models like RANS behave under more challenging conditions. Using higher fidelity LES simulations it is possible to assess the performance of RANS under such conditions and aid designers by highlighting short comings and improving the application of such tools.

Jake Leggett is a PhD candidate at the University of Southampton, studying loss prediction in axial compressors. Having previously done a bachelors in mechanical engineering followed by an MSc in CFD at Imperial College London. His interests are in compressible fluid dynamics and numerical methods, focussing on modelling behavior and the performance of numerical models in capturing physically realistic flows.

• ## Confirmation: Numerical investigations of hemodynamic changes in stented coronary arteries

Bo Jiang
University of Melbourne

9am Wednesday 5 April 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Incomplete stent apposition (ISA) is sometimes found in stent deployment at complex lesions, and it is considered to be one of the causes of post-stenting complications, such as late stent thrombosis and restenosis. The presence of ISA leads to large recirculation bubbles behind the stent struts, which can reduce shear stress at the arterial wall that retards neointimal formation process and thus lead to complications. Computational fluid dynamics (CFD) simulations are performed on simplified two-dimensional axisymmetric arterial models with stents struts of square and circular cross-sectional shapes at a malapposition distance of 120 μm from the arterial wall. Under the condition of the same flow rate, both square and circular strut cases show that shorter period provides greater flow deceleration, leading to the formation of a larger recirculation bubble. With the same thickness, circular strut has a significant improvement over the square strut in terms of the size of the recirculation bubble, and therefore less likely to lead to complications. We also carried out three-dimensional computational fluid dynamics studies on a partially embedded coronary stent. Stent struts are partially embedded in portion of the circular and elliptical artery's circumference and malaposed elsewhere. Maximum malapposition distances (MD) used in this study are 0.255 mm (moderate) and 0.555 mm (severe). Time-averaged wall shear stress (TAWSS) is used as the haemodynamic metric to evaluate the clinical significance of ISA. TAWSS decreases along the circumferential direction as MD decreases from the maximum ISA side to the embedded side. The case with severe ISA has a larger area of high TAWSS on the arterial wall at the proximal end and low TAWSS at the distal end of the stent.

• ## Theoretical framework for the upscaling of physical interactions in aquatic mobile-boundary flows

University of Melbourne, University of Aberdeen

4pm Tuesday 28 March 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Most environmental flows often exhibit high levels of spatial and temporal heterogeneity in hydrodynamic fields due to the effects of multi-scale roughness elements and their mobility. These effects are especially profound in the near-bed region. The development of a unifying framework for the integration and upscaling of the fluid mechanical, ecological and biomechanical processes occurring in such conditions is needed. Particular focus in this study is on the interactions of the fluid motion with the motions of aquatic plants and sediments in aquatic systems.

To cope with the temporal and spatial heterogeneity of the flow field near the flow interface with a second non-fluid phase, the governing equations of motion are averaged over time and space. To deal with the possible discontinuity of the averaged fields within the averaging domains, appropriate definitions and theorems for time and space averaging are used.

Appropriately formulated coupled double-averaged conservation equations are developed for fluid, sediment, and plant motions. Complementary equations for the second-order velocity moments introduced by the averaging process are also proposed. Due to the double-averaging methodology (i) the governing equations are up-scaled to the scales relevant to applications, (ii) the fluid motion is rigorously coupled with the non-fluid (plants or sediments) motions, and (iii) the effect of the moving interfacial boundary is introduced explicitly in the governing averaged equations.

This presentation introduces to the main concepts and key steps involved in the derivation of the double-averaged equations outlined above, discusses their application to the analysis of high-resolution data sets and identifies potential applications in mobile-boundary flow studies.

Konstantinos performed his PhD research on flow-biota and flow-sediment interactions in rivers and open-channel flows at the University of Aberdeen, where he was on a Marie-Curie Fellowship. Prior to that, he obtained an MSc in coastal engineering at the National Technical University of Athens (2013) and MEng in environmental engineering at the Technical University of Crete (2009).

• ## High resolution simulation of dissolving ice-shelves in sea water

Bishakhdatta Gayen
Research School of Earth Sciences, Australian National University

4pm Friday 24 March 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Precise knowledge of ocean dynamics and interactions with the grounded ice at high latitudes is very crucial for predicting the sea-level rise and further development of adaptation strategies in a warming global climate. The physics of these ocean–ice interactions particularly related to small scale processes, is poorly understood which, along with limited observation constraints, leads to uncertainties in the predictions of future melt rate. We perform high resolution numerical simulation to investigate dissolving of ice into cold and salty sea water. The three coupled interface equations are used, along with the Boussinesq and non-hydrostatic governing equations of motion and equation of state for seawater, to solve for interface temperature, salinity, and melt rate. The main focus is on the rate of dissolving of ice at ambient water temperatures between −1°C and 2°C and salinity around 35 psu and the dependence on stratification (as characterizes many sites around Antarctica). Our simulation also shows boundary layer next to the ice face is dominated by turbulent motions. It is also important to quantify the difference between the melting of a vertical ice wall and the melting of a sloping ice shelf. The basal slope is observed to vary significantly, due to the formation of crevasses, channels and terraces. Our high-resolution simulations are designed for direct comparison with laboratory measurements and theory. The temperature and density structures found under Pine Island Glacier show several layers having a vertical scale that can also be explained by this study.

Bishakhdatta Gayen received a degree in Bachelor of Mechanical Engineering from Jadavpur University in Kolkata, India in 2006, and a M.S. degree in Engineering Science, majoring in Fluid Mechanics, from the Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, in 2007. He was then awarded a University of California Graduate Fellowship and received an M.S. (2010) and Ph.D. (2012) from University of California, San Diego. He pursued research work on "Turbulence and Internal Waves in Tidal Flow over Topography" under the guidance of Prof. Sutanu Sarkar and was awarded the Andreas Acrivos Award for Outstanding Dissertation in Fluid Dynamics from the American Physical Society. He moved to Australia to pursue his postdoctoral research with Prof. Ross W. Griffiths at the Australian National University in Canberra. Bishakh is currently an Australian Research Council Discovery Early Career Fellow. His current research interests are nonlinear internal waves in the ocean, turbulent convection, modeling of Antarctic ice melting and Southern ocean dynamics.

• ## The vortices of V. Strouhal

David Lo Jacono
Institut de Mécanique des Fluides de Toulouse

4pm Friday 17 March 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

During this seminar, I will talk about the link between Strouhal's findings and vortices. We learn that the Strouhal number characterises the shedding frequency of vortices behind a bluff-body, yet Strouhal never encountered a vortex. I will try to show the role played by various well-known researchers (Rayleigh, Bénard, Kármán, etc.), and others that are less well known yet have a key role towards understanding wake dynamics. Starting from the motivation of Strouhal and ending with the modern analysis of wakes in 1930, I will try to build an incomplete and brief history of 19th-20th century (wake) fluid mechanics focussing on motivation and experimental insights. This work was originally part of my ScD dissertation and further completed for the recently held colloquium "A century of Fluid Mechanics 1870-1970" celebrating the IMFT century anniversary.

• ## Skin-friction and vorticity fields in wall-bounded flows and the attached eddy hypothesis

Min Chong
University of Melbourne

4pm Friday 10 March 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

The invariants of the velocity gradient tensor have been used to study turbulent flow structures in order to extract information regarding the scales, kinematics and dynamics of these structures. These invariants cannot be used to study structures at a no-slip wall since they are all zero at the wall. However, the flow structures at the wall can be studied in terms of the invariants of the "no-slip tensor". Employing surface flow patterns generated using local solutions of the Navier-Stokes equations, the relationship between the surface skin-friction field and vorticity field will be explored. These local solutions, together with data from the Direct Numerical Simulations of channel flows, pipe flows and boundary layer flows may perhaps lead to a better model for the structure of attached eddies in wall bounded flows.

• ## Linear estimation of large-scale structures in channel flow at Reτ = 1000

Simon Illingworth
University of Melbourne

4pm Friday 3 March 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Given the time-resolved velocity field in a plane at a single wall-normal height, how well can one estimate, using a linear model alone, the time-resolved velocity field at other wall-normal heights? This question will be explored for channel flow at Reτ = 1000 using data from the John Hopkins Turbulence database. Two different linear models will be explored. Each linear model has its origins in the Navier–Stokes equations.

• ## Subfilter-scale stress modelling for large-eddy simulations

Amirreza Rouhi
University of Melbourne

4pm Friday 24 February 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

A subfilter-scale (SFS) stress model is developed for large-eddy simulations (LES) and is tested on various benchmark problems in both wall-resolved and wall-modelled LES. The basic ingredients of the proposed model are the model length-scale, and the model parameter. The model length-scale is defined as a fraction of the integral scale of the flow, decoupled from the grid. The portion of the resolved scales (LES resolution) appears as a user-defined model parameter, an advantage that the user decides the LES resolution.

The model parameter is determined based on a measure of LES resolution, the SFS activity. The user decides a value for the SFS activity (based on the affordable computational budget and expected accuracy), and the model parameter is calculated dynamically. Depending on how the SFS activity is enforced, two SFS models are proposed. In one approach the user assigns the global (volume averaged) contribution of SFS to the transport (global model), while in the second model (local model), SFS activity is decided locally (locally averaged). The models are tested on isotropic turbulence, channel flow, backward-facing step and separating boundary layer.

In wall-resolved LES, both global and local models perform quite accurately. Due to their near-wall behaviour, they result in accurate prediction of the flow on coarse grids. The backward-facing step also highlights the advantage of decoupling the model length-scale from the mesh. Despite the sharply refined grid near the step, the proposed SFS models yield a smooth, while physically consistent filter-width distribution, which minimizes errors when grid discontinuity is present.

Finally the model application is extended to wall-modelled LES and is tested on channel flow and separating boundary layer. Given the coarse resolution used in wall-modelled LES, near the wall most of the eddies become SFS and SFS activity is required to be locally increased. The results are in very good agreement with the data for the channel. Errors in the prediction of separation and reattachment are observed in the separated flow, that are somewhat improved with some modifications to the wall-layer model.

Amirreza Rouhi is a postdoctoral fellow in the fluids group at the university of Melbourne. Amirreza received his PhD in Mechanical Engineering from Queen's University of Canada under supervision of Prof. Piomelli, doing subfilter-scale (SFS) stress modelling as his PhD thesis. His other research interests include wall-modelled LES, spectral methods and rotating turbulence.

• ## Completion: The minimal-span channel for rough-wall turbulent flows

Michael MacDonald
University of Melbourne

4pm Friday 10 February 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Turbulent flows over roughness are ubiquitous in engineering and geophysical applications, however their effects are primarily given through semi-empirical models and approximations. The accuracy of these methods is sensitive to the model and roughness topology in question, so that laboratory experiments and conventional direct numerical simulations (DNS) remain the desired standard in rough-wall studies. However, these techniques are expensive for both industry and researchers, making design predictions and the examination of rough-wall flows challenging. In this talk, we outline a framework termed the minimal-span channel in which fully resolved numerical simulations of rough-wall flows can be conducted at a reduced cost compared to conventional DNS. The minimal-span channel is used to simulate turbulent flow over a variety of roughness geometries that would otherwise be prohibitively expensive to study. Special attention is given to recent simulations of rectangular bars aligned in the spanwise direction, commonly called d-type roughness.

• ## Completion: Reorganising turbulence using directional surface patterns

Kevin
University of Melbourne

4pm Wednesday 1 February 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

We attempt to passively reorganise wall turbulence using transitionally-rough surface patterns in the form of herring-bone riblets. The flow fields are investigated experimentally using large field-of-view particle image velocimetry in all orthogonal planes. The pronounced modification of the boundary layer suggests that a preferential arrangement of the naturally-occurring turbulence events may have been introduced. The spatial information captured in these multiple orientations enable us to clearly observe distinct turbulence events, such as the unstable outer layer, non-symmetrical vortical motions and strong streamwise-periodic events. Interestingly, our recent analysis indicates that the aforementioned events we thought was induced by the surface pattern, though weaker, are actually present in the smooth-wall (canonical) flows. In the average picture however, these structural attributes are masked by their random occurrences in space. This further suggests that we can passively reposition and perhaps manipulate large turbulence structures.

• ## DNS study on relation between vorticity and vortex

Chaoqun Liu
University of Texas at Arlington, Texas, USA

2pm Monday 23 January 2017
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Vorticity, vorticity line, vorticity tube have rigorous mathematical definition, but the rigorous definition of vortex is still an open question. However, for long time until now, in many research papers and text books, vortex is defined as vorticity tube confined by vorticity lines without vorticity line leakage. Vortex is also considered as congregation of vorticity lines with larger vorticity. Our DNS study shows that vortex is not a vortex tube but open for vorticity line penetration, is not a congregation of vorticity lines but a dispersion of vorticity lines, is not a concentration of vorticity with larger vorticity but with smaller vorticity in most 3-D cases. In general, vortex is an intuitive concept of rotation core with weak dissipation, e.g. zero dissipation when it becomes rigid rotation. In addition, vortex is not a vorticity tube, being different from what suggested by many research papers and textbooks. At the laminar boundary layer, vorticity is large but we have no vortex. A core with 2 nearly pure rotations per second, where vorticity is small, is a vortex, but a core with 10000 strongly sheared rotation, where vorticity is very large but deformation is very large as well, may not be a vortex. Therefore, vorticity magnitude and vortex are irrelevant. Unlike solid body, vortex is always a mixture of vorticity and deformation and vortex is really defined as an open area (not tube) where deformation is weak and vorticity is dominant. A function so-called "Omega" is defined to identify the vortex and Omega=0.52 well represents the vortex area boundary. Vortex is mathematically defined as Omega >0.5 which means a place where vorticity overtakes deformation. The minimum gradient of "Omega" is well representing the vortex axis. Several examples including DNS for late flow transition and LES for shock vortex interaction have been tested and the outcome is promising.

Chaoqun Liu is a Distinguished Professor and CNSM Center Director in the Department of Mathematics, University of Texas at Arlington, Arlington, Texas, USA.

• ## Completion: The structure and scaling of rough-wall turbulent boundary layers

Dougal Squire
University of Melbourne

2pm Wednesday 21 December 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Turbulent wall layers are a pervasive and influential feature in nature and engineering; common examples include the atmospheric and benthic layer (relevant to weather prediction and pollutant dispersion, for example), boundary layers developing on aerial, marine and terrestrial vehicles (such as aeroplanes, naval vessels, cars and trains), and flows in piping networks. These flows are characterised by high Reynolds numbers and, more often than not, surface roughness that exerts a dynamical effect on the flow. The latter may result from manufacturing defects, erosion and/or deposition, including that of living organisms. In this talk, we will present results from recent measurements of rough-wall turbulent boundary layers spanning a very wide range of friction and roughness Reynolds numbers. The results comprise 38 datasets and four experimental techniques, including hot-wire anemometry and particle image velocimetry. Our analysis will focus broadly on the relationship between the outer region flow and near-wall structures which are directly influenced by the roughness scale(s). Features of this relationship will be discussed using single-point statistics, measures of spatial structure, and the inner-outer interaction model of Marusic et al. (Science, 2010, vol. 329, pp. 193–196).

• ## Confirmation: Entrainment and interface dynamics of turbulent plumes

Himanshu Mishra
University of Melbourne

10am Wednesday 9 November 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Turbulent plumes form when a fluid of one density is injected into another quiescent fluid with a different density. From violent volcanic eruptions to the smoke rising from a cigarette, turbulent plumes are omnipresent in nature at wide range of scales. One of the fundamental aspects in the understanding of turbulent plumes is the process of 'entrainment', the mixing of surrounding fluid into the plume. Unlike non-buoyant flows, plumes pose a challenge in using common optical measurement techniques like particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF), because of the local changes in refractive index, when two fluids mix. This has led to most of the previous research being focused on global measurements of entrainment, whereas the local measurements, which are required for clearer understanding the entrainment phenomenon are practically non-existent. One of the ways to circumvent this problem is to match the refractive index of two solutions while maintaining the density difference, by adding certain chemicals to them. Alternatively, a measurement technique named Background Oriented Schlieren (BOS), which uses the local refractive index changes to quantify the local density variations, can be used.

With the final aim of understanding the process of entrainment in turbulent plumes, we present preliminary results for two experimental studies. (i) Velocity measurements in a vertical round axisymmetric turbulent jet in a newly constructed experimental facility, and (ii) free settling sphere in a sharp density interface using BOS.

• ## Hydrodynamic forces on geometrically porous structures

Scott Draper
University of Western Australia

4pm Friday 28 October 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Prediction of hydrodynamic forces on geometrically porous structures is important for many applied problems in offshore engineering. However, the accurate prediction of these forces is complicated by the fact that the bulk velocity of the flow passing through a porous structure is a function of its porosity. In this talk I will present a theoretical model built on control volume arguments which may be used to estimate the bulk velocity of the flow passing through an isolated porous structure and, in turn, the resulting hydrodynamic force on the structure. Extensions of the model will be introduced to consider multiple porous structures in close proximity, inviscid shear flow and non-uniform porosity. It will be shown how these extensions have been used in recent work to optimise the layout of wind and tidal turbine arrays, estimate forces on offshore space frame structures and predict the flow through patches of aquatic vegetation.

Dr Scott Draper is a senior lecturer at the University of Western Australia. His research focuses on offshore fluid mechanics applied mostly to the oil and gas and renewable energy industries. This has included research on the stability of subsea infrastructure, the optimum arrangement of marine renewable energy devices and the hydrodynamics of floating bodies. He is fortunate to work with numerous industry partners including Shell, Woodside and Carnegie Wave Energy.

• ## Pulse-burst PIV in high-speed flows

Steven Beresh
Aerosciences Department Sandia National Laboratories

4pm Wednesday 26 October 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Time-resolved particle image velocimetry (TR-PIV) has been achieved in a high-speed wind tunnel and a shock tube, providing velocity field movies of compressible turbulence events. The requirements of high-speed flows demand greater energy at faster pulse rates than possible with the TR-PIV systems developed for low-speed flows. This has been realized using a pulse-burst laser to obtain movies at up to 50 kHz with higher speeds possible at the cost of spatial resolution. The constraints imposed by use of a pulse-burst laser are a limited burst duration of 10.2 ms and a low duty cycle for data acquisition. Pulse-burst PIV has been demonstrated in a supersonic jet exhausting into a transonic crossflow and in transonic flow over a rectangular cavity. The velocity field sequences reveal the passage of turbulent structures and can be used to find velocity power spectra at every point in the field, providing spatial distributions of acoustic modes and revealing turbulence scaling laws. Additional applications in a shock tube show the transient onset of a von Kármán vortex street shed from a cylinder and particle drag in a shocked dense gas-solid flow. The present work represents the first use of TR-PIV in a high-speed ground test facility.

Steven J. Beresh is a Distinguished Member of the Technical Staff at Sandia National Laboratories in Albuquerque, New Mexico, U.S.A., where he has worked since 1999 and currently leads the Experimental Aerosciences Facility. He received his B.S. in Mechanical Engineering from Michigan State University in 1994 and his Ph.D. in Aerospace Engineering from The University of Texas at Austin in 1999. His research interests emphasize the use of optical diagnostics for compressible aerodynamics, particularly particle image velocimetry, but utilize a variety of laser-based instrumentation techniques and high-frequency surface sensors. He also is responsible for a wide range of wind tunnel testing and facility operation. He is an Associate Fellow of the American Institute for Aeronautics and Astronautics, the Chair for the AIAA Aerodynamic Measurement Technology Technical Committee, and is a past President of the Supersonic Tunnel Association International.

Ramis Örlü
KTH Royal Institute of Technology Sweden | Website

4pm Friday 14 October 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

In this talk, we discuss a number of different aspects pertinent to zero pressure gradient (ZPG) turbulent boundary layers (TBLs), and extend these to moderate and strong adverse pressure gradients (APGs). We start out with inflow and tripping effects in ZPG TBLs and show their persistence in the outer layer beyond Reynolds numbers (Re) that could be reached just few years ago by means of direct numerical simulations (DNS). When it comes to APG TBLs, the situation has usually been more blurry when considering literature data, due to their dependency on the pressure-gradient strength and streamwise history, besides Reynolds number effects. Based on different APG TBLs developing on flat plates and the suction side of a wing, we aim at distinguishing the importance of these parameters based on well-resolved in-house large-eddy and direct numerical simulations as well as wind tunnel experiments.

A recurring tool in the investigation of these topics is the diagnostic-plot concept, which indicates a linear dependence between the turbulence intensity and its mean velocity and turns out to be useful when establishing a well-behaved state in the outer layer of wall-bounded turbulent flows and determining the boundary layer edge in strong PG cases or TBLs on curved surfaces. A possible analogy between high-Re ZPG TBL flows and strong APG TBLs is also considered in light of negative wall-shear stress events.

Dr. Ramis Örlü received his M.Sc. (Dipl-.Ing.) in 2003 from the Ruhr University of Bochum, Germany in Mechanical Engineering and holds a Ph.D. in Fluid Mechanics (2009) KTH Royal Institute of Technology, Stockholm, Sweden. His research is focused on experimental methods and wall-bounded turbulent flows. Since 2009 and 2015 he works as a researcher and docent (in Experimental Fluid Physics), respectively, at the Linné FLOW Centre located at KTH. His research portfolio covers the experimental investigation of wall-bounded turbulent flows with strong numerical collaborations. Other active areas cover measurement technique development/correction for high-Reynolds number wall-bounded flows as well as applications in internal combustion engine related flows and various flow control strategies for separation delay and skin-friction drag reduction. Dr. Örlü has about 50 journal publications, and a wide network with other researchers in wall-bounded turbulence research.

• ## Experimental investigation of two-phase flows in naval hydrodynamics

Paul Brandner
Australian Maritime College University of Tasmania

4pm Thursday 29 September 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Flow about ships and submarines vary from pure liquid-gas to pure liquid-vapour two-phase flows. They involve a large range of spatial and temporal scales and physical phenomena such that gaining insight remains a challenge via either experiment or computation. Naturally occurring microbubble populations in the ocean are of particular interest due to their potential to both affect and be affected by various phenomena and flow processes. They provide nuclei for cavitation inception on lifting surfaces of ships and submarines. Surface ships are prolific sources of polydisperse bubble populations that add to bubbly disperse flows about lifting surfaces. Cavitation and turbulence ultimately create complex long-lived large-scale microbubble laden wakes with properties significantly altered compared with those of the outer fluid. Techniques and results on various two-phase flow experiments in naval hydrodynamics are presented including microbubble generation for artificial seeding of nuclei and for PIV, microbubble disperse flows, cavitation inception, macroscopic cavitation phenomena, supercavitation, millimetre-bubble break and coalescence in turbulent shear flows and fluid-structure interaction.

Paul Brandner is research leader of the Cavitation Research Laboratory at the Australian Maritime College. His research interests include cavitation inception and dynamics, bubbly flows, supercavitation, fluid-structure interaction and hydroacoustics.

• ## Completion: Numerical simulations of two-phase flow: Eulerian and Lagrangian predictions

Shuang Zhu
University of Melbourne

4.15pm Friday 16 September 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

The term two-phase flow refers to any fluids flow of two coexisting media in motion. The difference between the media can be its thermodynamic state, called phase (e.g. gas, liquid or solid) and/or its multiple chemical components. Two-phase flow is common in many environmental systems including rain, snow, sandstorms, avalanches, sediment transport debris flow and countless other natural phenomena. It is also of extreme importance in many industrial and engineering applications, such as fluidised bed, droplet spray process, drug aerosol delivery, dense gas dispersion, particle deposition and pollution control.

A persistent theme throughout the study of two-phase flow is the need to model the detailed behaviour of these flow phenomena as the ability to predict the behaviour of these flow systems is central to safety, efficiency and effectiveness of those events and processes. Similar to single-phase flow research, the development of predictive models for the two-phase flow follows along three parallel paths, namely theoretical models, laboratory experiments and numerical simulations. There are some cases where full-scale experimental models and/or accurate theoretical models are possible. However, in many other cases, the use of those models can be impossible for many of reasons. Consequently, the predictive capability and physical understanding of two-phase flow problems heavily rely on the employment of numerical simulations. The study of dynamics of two-phase flow using high resolution numerical simulations has gained considerable momentum with the recent development in computational fluid dynamics (CFD) methodologies. In particular, the use of direct numerical simulations (DNS) resolves the entire range of spatial and temporal scales of the fluid motion, which provides new insights into the structure and dynamics of the two-phase flow.

Current two-phase flow simulations modelling can be broadly classified based on the treatment of the dispersed phase. Two types of approaches are prevalent, Eulerian approach and Lagrangian approach, which are based on the concept of the continuous phase described in the Eulerian reference frame in a flow domain with the dispersed phase described either in the Eulerian reference frame as the continuous phase, leading to the Eulerian approach (commonly known as the "two-fluid" model), or in the Lagrangain frame, leading to the Lagrangain approach (also known as the "trajectory" model). The primary motivation behind the present work is to perform high fidelity numerical simulations to study two-phase flow using both Eulerian and Lagrangian approaches on three different two-phase flow problems, namely gravity currents, particle-laden currents and enhanced targeted drug delivery in a vascular tree.This PhD work provides a much needed knowledge on different two-phase flow numerical modelling approaches by solving the aforementioned real life scenarios. Specifically, the success of this PhD work would lead to better two-phase computational fluid dynamics strategy.

• ## Statistical characteristics of fully nonlinear potential deep water wave fields

Elena Sanina
Department of Infrastructure Engineering, University of Melbourne

4pm Friday 12 August 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

We present an analysis of long-term wave simulations performed using a fully nonlinear potential deep water wave model. The results of the simulations are compared with the spectra obtained using a variety of directional methods and are discussed in the context of their applications. The short-crestedness of a wave field is investigated in terms of the three-dimensional steepness defined as the vector whose magnitude is equal to the average steepness calculated along the vector direction in a horizontal plane. Several statistical characteristics of the surface elevation field and the wave spectrum development such as a non-uniformity of the wave spectrum and a migration of its peaks are discussed. The appearance of coherent structures on the ocean surface closely related to the tendency of high waves to occur in groups is analysed. Various features of the identified groups such as velocity of the groups, their lengths, lifetime and steepness are studied. A general analysis of the number of detected groups is also performed for the computed wave fields.

Dr. Elena Sanina is a Research Fellow in Ocean Engineering at the Department of Infrastructure Engineering, University of Melbourne. With Bachelor and Master degrees in Pure Mathematics from the Voronezh State University (Russia), she continued her studies performing research in the area of applied mathematics. In 2015 she completed her PhD in the Centre for Ocean Engineering, Science and Technology (COEST) at Swinburne University of Technology, then continued her work at the University of Melbourne in May 2016. Her research interests include non-linear waves, extreme waves and wave statistics.

• ## Completion: Evolution of zero pressure gradient turbulent boundary layers

Will Lee
University of Melbourne

4pm Monday 8 August 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

An experimental investigation of evolving turbulent boundary layers in a tow tank facility is presented. The main aim is to study the dynamics and the development of coherent features in a turbulent boundary layer from the trip to a high-Reynolds number state. With this goal in mind, time-resolved particle image velocimetry measurements are performed with a towed plate to provide a unique view of the streamwise evolution of turbulent boundary layers. The merit of this temporally-resolved dataset is it enables us to investigate the evolving dynamic properties of coherent features specifically in the outer region of turbulent boundary layers. The results reveal the formation mechanism and temporal evolution of shear layers and their associated large-scale coherent motions. Based on these findings, a conceptual model which describes dynamic interactions of coherent features is proposed and discussed.

• ## Self-sustaining motions and periodic orbits in statistically stationary homogeneous shear turbulence

Atsushi Sekimoto
Monash University

4pm Friday 5 August 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Homogeneous shear turbulence (HST) is the most canonical flow to investigate the shear-induced turbulence, where it is known that there are coherent structures, like velocity streaks and streamwise elongated vortices, similar to wall-bounded flows. The coherent structures and their dynamics are considered as incomplete realisations of nonlinear invariant solutions in the incompressible Navier–Stokes equation, i.e. equilibrium solutions or periodic orbits, which have been reported in the plane Couette, Poiseuille, pipe flow, isotropic turbulence, and so on. In this study, unstable periodic orbits (UPOs) in HST are investigated. The ideal HST grows indefinitely, and in simulations, the growing integral scale reaches the size of the computational domain. The largest-scale motion is restricted by the computational domain, and it grows, break-downs, and regenerates quasi-periodically, reminiscent to the self-sustaining motion and bursts in wall-bounded flow. The long term simulation of HST reaches the statistically stationary state. Direct numerical simulations (DNS) of statistically stationary homogeneous shear turbulence (SS-HST) are performed by a newly developed code. The box dependency is investigated to establish 'healthy' turbulence in the sense that the turbulence statistics are comparable to wall-bounded flow. SS-HST is essentially a minimal flow, and constrained by the spanwise box dimension as in minimal channel flow (Sekimoto, Dong & Jiménez, 2016 Phys. Fluids 28:035101; Flores & Jiménez 2010 Phys. Fluids 22:071704). In these good boxes, UPOs are numerically obtained. It represents a regeneration cycle of streamwise vortices and a streak, similar to the self-sustaining process (SSP) in wall-bounded flow.

The speaker received a PhD in thermo-fluid mechanics from Osaka University in 2011. He joined the Fluid Mechanics group in the Technical University of Madrid (UPM) as postdoctoral fellow. He is now a research fellow in the Laboratory for Turbulence Research in Aerospace & Combustion (LTRAC) in Monash University.

• ## Fluid mechanic challenges at DST Group: from submarines to hypersonic vehicles

Malcolm Jones
Defence Science and Technology Group

4pm Friday 29 July 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

The physics of fluid flow plays a dominant role in modelling vehicles traveling through the atmosphere or oceans. Whether it is predicting the drag experienced on a submarine, the lift generated by a flapping wing micro air vehicle or the heating loads acting a hypersonic vehicle. The Navier–Stokes equations governing these flows are known, but except for a few trivial cases cannot be solved directly. For this reason a range of alternative methods must be used. These include: approximations to the equations, numerical solutions, laboratory scale experiments and field trials. This talk will discuss how these methodologies are applied Defence Science and Technology Group to three example research areas: submarine hydrodynamics, flapping wing aerodynamics and hypersonic aerodynamics. While these vehicles appear diverse there is a common theme in the technical challenges and hence in the scientific approach taken.

Malcolm Jones received a PhD in fluid mechanics from The University of Melbourne in 1998. He received a degree in mechanical engineering from the same university in 1994. He joined the Defence Science and Technology Group in 2007 where he is currently employed as a Research Scientist in the Aerospace Division. Malcolm currently works on a range of diverse research projects which include: aerodynamics of flapping wings, aerodynamics of hypersonic vehicles (HIFiRE program), cavity aeroacoustics, boundary layer transition, and submarine hydrodynamics. Prior to joining DSTO he was employed as Research Fellow and lecturer in the Department of Mechanical Engineering at The University of Melbourne and also at the School of Mathematical Sciences, Queensland University of Technology.

• ## Confirmation: DNS of a turbulent line plume in a confined region

Nitheesh George
University of Melbourne

4pm Thursday 28 July 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

We present results from a direct numerical simulation (DNS) of a turbulent line plume in a confined region with adiabatic side, top and bottom walls. The plume originates from a local line heat source of length, L, located at the centre of the bottom wall (z/H = 0) and it rises until it hits the top wall (z/H = 1) and spreads laterally to produce a buoyant fluid layer. Since the region is confined, the continuous supply of buoyant fluid forces the layer downwards, until it reaches the bottom wall, where the flow is said to be the asymptotic state (Baines and Turner 1969). In the present case, two Reynolds numbers, 3840 and 7680, are selected for plume lengths, L/H = 1, 2 and 4, where the Reynolds number of the plume is based on H and the buoyant velocity scale, F01/3, where F0 is buoyancy flux per unit length. The current simulations are validated against the analytical model presented by Baines and Turner (1969). The simulations exhibit a slow flapping motion of the confined line plume in the asymptotic state, which precludes a straightforward comparison with Baines and Turner's analytical model. For the purpose of comparing the analytical model, we have adapted a shifting method introduced by Hubner (2004), which improves agreement with the analytical model.

• ## Confirmation: Optimal actuator and sensor placement for feedback flow control using the complex Ginzburg–Landau equation

Stephan Oehler
University of Melbourne

4pm Friday 8 July 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

The process of selecting the optimal actuator and sensor positions for a single-input single-output flow control problem is investigated and its limitations are discussed. Multiple unstable modes and time delays between actuating and sensing often result in a challenging flow control problem. Previous approaches have focused on the use of modern control schemes, but these do not always provide the full picture and difficult control problems are often predicated on fundamental limitations, which are not made clear in a modern control framework. In this paper, a previously developed control scheme for the complex Ginzburg–Landau equation is presented, the challenges for different set-ups are analysed and it is shown how fundamental limitations can lead to an intractable control problem. The research explores the control schemes developed for the complex Ginzburg–Landau equation from the fundamental perspective, while further connecting the two fields of fluid dynamics and control theory.

• ## The mitigation of pulsation in ventilated supercavities

Grant Skidmore
University of Melbourne

4pm Friday 1 July 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

It is possible for an underwater body to greatly reduce the drag caused by skin friction, using ventilated supercavitation. While the idea of ventilated supercavitation works well in theory, the process of generating a ventilated supercavity in practice is often plagued by pulsation. When a supercavity pulsates, the walls of the supercavity begin to periodically expand and contract. This can lead to the supercavity walls clipping the body, which can become problematic for stability of the supercavitating body. This seminar will explore the internal cavity pressure and near-field noise generated by experimental and computational supercavities. The results of the acoustic study revealed that the radiated acoustic pressure of pulsating supercavities is at least 40 dB greater than comparable twin vortex and re-entrant jet supercavity closure regimes. For pulsating supercavities it was also found that, at the pulsation frequency, the cavity interior pressure spectrum level was related to the near-field and far-field noise spectrum level through spherical spreading of the sound waves from the supercavity interface. As a result, the cavity interior pressure can be used as a measure of the radiated noise. The oscillatory nature of the internal cavity pressure time history was used to develop a method to mitigate supercavity pulsation. The method was explored with a numerical model, experiments, and CFD. The method is based on modulating the ventilation rate injected into a ventilated supercavity with the addition of a sinusoidal component. The effect of this modulation is the ventilated supercavity being effectively driven away from the resonance frequency. A wide range of ventilation rate modulation frequencies can cause the pulsating supercavity to transition into twin vortex closure. A reduction in the radiated noise accompanies the transition from pulsation to twin vortex closure, oftentimes 35 dB or more. Other modulation frequencies do not suppress pulsation but change the supercavity pulsation frequency.

Grant Skidmore is a postdoctoral researcher in Mechanical Engineering at the University of Melbourne. Grant obtained his PhD in aerospace engineering at the Pennsylvania State University. His research interests include supercavitation, drag reduction, hydrodynamic stability, free surface flows, multiphase flows, and turbulent wakes.

• ## Confirmation: Geometric aspects of wall-flow dynamics

Rina Perven
University of Melbourne

4pm Tuesday 28 June 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Complex but coherent motions form and rapidly evolve within wall-bounded turbulent flows. Research over the past two decades broadly indicates that the momentum transported across the flow derives from the dynamics underlying these coherent motions. This spatial organization, and its inherent connection to the dynamics, motivates the present dissertation research. The local field line geometry pertaining to curvature (κ) and torsion (τ) has apparent connection to the dynamics of the flow, and preliminary results indicate that these geometrical properties change significantly with wall-normal position. One part of this research is thus to clarify the observed changes in the field line geometry with the known structure and scaling behaviours of the mean momentum equation. Towards this aim, the planar curvature of the streamlines at each point in streamwise–spanwise slices of existing boundary layer DNS has been computed for different wall-locations. The computation of κ and τ arise from the local construction of the Frenet–Serret coordinate frame. The present methods for estimating κ and τ are briefly described, as is the need to improve the efficiency of this computation. The present results are briefly described, as are the broader aims to better understand the relationships between the geometry and dynamics of wall-flows. A schedule of the future work to be conducted is outlined.

• ## Laser light sheet profile and alignment effects on PIV performance

Kristian Grayson
University of Melbourne

11am Monday 27 June 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

The sensitivity and impact of laser profile misalignment and shape mismatch on Particle Image Velocimetry (PIV) measurements are investigated in this study. While the effects of laser profile misalignment can be equivalent to an out-of-plane velocity component, light sheet mismatch can be identified and corrected prior to an experiment, decreasing PIV uncertainties. Synthetic particle image simulations are used to isolate and systematically vary laser profile mismatch parameters between successive PIV laser pulses. Two simulation cases are discussed, analysing the effects of a misalignment between two otherwise identical laser pulses, as well as a mismatch in the width of two laser profiles. Our results reveal a steady degradation in mean correlation coefficient as the laser profiles are increasingly mismatched in shape and alignment, coupled with a rapid rise in the detection of spurious vectors. These findings reinforce the need to consider laser sheet alignment and intensity distribution when seeking to capture high quality PIV measurements. The design of a modular and inexpensive laser profiling camera is outlined to enable robust and repeatable quantification of laser sheet overlap and beam characteristics. The profiling system is also found to be a valuable tool for laser diagnostics and aiding the setup of experiments. Various potential applications of this device are presented for PIV and other laser-based measurement techniques. Finally, preliminary results from PIV experiments which involve the deliberate misalignment of laser profiles are discussed. These data reiterate the trends observed in simulations, but also emphasise the coupled complexity of laser profile mismatch behaviour in experimental scenarios, placing the idealised simulation results in some context. Collectively, our findings highlight the importance of well-matched laser profiles. A more rigorous experimental quantification of these behaviours has the potential to enhance the quality of PIV results.

• ## Towards a Moody-like diagram for turbulent boundary layers

Dale Pullin
Graduate Aerospace Laboratories, California Institute of Technology

4pm Friday 24 June 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

An empirical model is presented that describes a fully developed turbulent boundary layer in the presence of surface roughness with a nominal roughness length-scale that varies parametrically with stream-wise distance. For Reynolds numbers based on the outer velocity and stream-wise distance that are large, use is made of a simple model of the local turbulent mean-velocity profile that contains the Hama roughness correction for the asymptotic, fully rough regime. It is then shown that the skin friction coefficient is constant in the streamwise direction only for a linear streamwise roughness variation. This then gives a two parameter family of solutions for which the principal mean-flow parameters can be readily calculated. Results from this model are discussed for the zero-pressure-gradient turbulent boundary layer, and some comparisons with the experimental measurements of Kameda et al. (2008) are made. Trends obtained from the model are supported by wall-modeled, large-eddy simulation (LES) of the zero-pressure-gradient turbulent boundary layer at very large Reynolds numbers. Both model and LES results are consistent with the self-preservation arguments of Talluru et al. (2016). It is argued that the present model/LES can be interpreted as providing the asymptotically rough-wall equivalent of a Moody-like diagram for turbulent boundary layers in the presence of small-scale wall roughness.

The speaker is the von Kármán Professor of Aeronautics at the California Institute of Technology. His research interests include computational and theoretical fluid mechanics, vortex dynamics, compressible flow and shock dynamics, turbulence, and large-eddy simulation of turbulent flows.

• ## The universal nature of freestream coherent structures

Philip Hall
Monash University

4pm Friday 17 June 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Exact coherent structures are nonlinear solutions of the Navier Stokes equations not necessarily arising as bifurcations from a base state. The solutions are thought to be relevant to bypass transition and fully turbulent flows. There are two fundamental types of solutions: vortex-wave interaction states and freestream coherent structures. A brief survey of the field is given and then freestream coherent structures are discussed in detail. These are shown to be driven in a nonlinear layer located where the base flow adjusts to its freestream value through exponentially small terms. It is shown that they are implicated in the production of passive near wall streaks in a layer distant log R from the wall where R is the Reynolds number. They are shown to be canonical states relevant to any 2D boundary layer, vortex sheet, jet or wake and relevant to weakly 3D forms of the latter flows. Remarkably it turns out that they also exist in any fully developed flow having a local maximum of the unperturbed velocity field. The relevance to fully turbulent flows is discussed.

Professor Philip Hall is the Head of School of Mathematics, Monash University. Professor Hall is presently on leave from Imperial College, where he became the first Director of the Institute of Mathematical Sciences and where he has been the Director of LFC (Laminar Flow Control)-UK. His research interests are in applied mathematics, particularly in nonlinear hydrodynamic stability theory, computational fluid dynamics, boundary layer control, convection, lubrication theory, chaotic fluid motion, geomorphology of rivers and coherent structures in high Reynolds number flows.

• ## A voyage from the shifting grounds of existing data on zero-pressure-gradient turbulent boundary layers to infinite Reynolds number

Hassan M. Nagib
Illinois Institute of Technology, Chicago, USA

4pm Friday 10 June 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Aided by the requirement of consistency with the Reynolds-averaged momentum equation, the 'shifting grounds' are sufficiently consolidated to allow some firm conclusions on the asymptotic expansion of the streamwise normal stress normalized with the friction velocity; i.e. <u+u+>. A detailed analysis of direct numerical simulation data very close to the wall reveals that its inner near-wall asymptotic expansion must be of the form f0(y+) − f1(y+) / U+ + O(U+)−2, where f0 and f1 are O(1) functions fitted to data. This means, in particular, that the inner peak of the normal stress does not increase indefinitely as the logarithm of the Reynolds number but reaches a finite limit. The outer expansion of the normal stress <u+u+>, on the other hand, is constructed by fitting a large number of data from various sources. This exercise, aided by estimates of turbulence production and dissipation, reveals that the overlap region between inner and outer expansions of <u+u+> is its plateau or second maximum, extending to ybreak+ = O(U+), where the outher logarithmic decrease towards the boundary layer edge starts. The common part of the two expansions of <u+u+>, i.e. the height of the plateau or second maximum, is of the form A − B / U+ + ... with A and B constant. As a consequence, the logarithmic slope of the outer <u+u+> cannot be independent of the Reynolds number as suggested by 'attached eddy' models but must slowly decrease as 1 / U+. A speculative explanation is proposed for the puzzling finding that the overlap region of <u+u+> is centered near the lower edge of the mean velocity overlap, itself centered at y+ = O(1 / Reδ*0.5) with Reδ* the Reynolds number based on free stream velocity and displacement thickness. Similarities and differences between <u+u+> in ZPG TBLs and in pipe flow will be briefly discussed. Finally, the composite profile of <u+u+> is used with our mean velocity composite profile to demonstrate the detailed behavior of the so-called "diagnostic plot" with Reynolds number.

Professor Nagib is the John T. Rettaliata Distinguished Professor of Mechanical and Aerospace Engineering at the Illinois Institute of Technology, Chicago, Illinois, and the Founding Director of the Institute's Fluid Dynamics Research Center. His field of specialty is in fluid mechanics, turbulent flow and flow management and control. Professor Nagib is the recipient of a number of prestigious honors including being a Fellow of the American Physical Society, the American Association of Advancement of Science, the American Institute of Aeronautics and Astronautics, and the American Society of Mechanical Engineers.

• ## Large-amplitude flapping of an inverted-flag in a uniform steady flow

School of Mathematics and Statistics, University of Melbourne | Website

4pm Friday 3 June 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

The dynamics of a cantilevered elastic sheet, with a uniform steady flow impinging on its clamped-end, have been studied widely and provide insight into the stability of flags and biological phenomena. Recent measurements show that reversing the sheet's orientation, with the flow impinging on its free-edge, dramatically alters its dynamics. In contrast to the conventional flag, which exhibits (small-amplitude) flutter above a critical flow speed, the inverted-flag displays large-amplitude flapping over a finite band of flow speeds. In this talk, a combination of mathematical theory, scaling analysis and measurement is used to investigate the origin of this large-amplitude flapping motion. Flapping is found to be periodic predominantly, with a transition to chaos as flow speed increases. These findings have implications to leaf motion and other biological processes, such as the dynamics of hair follicles, because they also can present an inverted-flag configuration. This collaborative work is with the Gharib group at the California Institute of Technology.

John E. Sader is a Professor in the School of Mathematics and Statistics, The University of Melbourne. He leads a theoretical group studying a range of topics including the dynamic response of nanoparticles under femtosecond laser excitation, mechanics of nanoelectromechanical devices, high Reynolds number flow of thin films and rarefied gas dynamics in nanoscale systems.

• ## Turbulent horizontal convection and heat transfer

Bishakhdatta Gayen
Research School of Earth Sciences, Australian National University | Website

4pm Friday 27 May 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Horizontal convection (HC) is driven by a horizontal difference in temperature or heat flux at a single horizontal boundary of a fluid. In a thermally equilibrated state, net heat flux over the boundary is zero and circulation cell involves a horizontal boundary flow, turbulent plume motion at the end wall, and interior return flow which covers the entire the flow domain. HC may be a simple model of the meridonial overturning circulation (also known as global thermohaline circulation) based on such convective flow.

I will present three-dimensional convective circulation under differential heating on a single horizontal boundary of a rectangular channel, using direct and large eddy simulations over a wide range of Rayleigh numbers, Ra ∼ 108–1015. 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 ≥ 1010, while both dynamical balances give Nu ∼ Ra1/5. We have recently extended our study on circulation by applying thermal forcing on a lengthscale smaller than the domain, and with variation in both horizontal directions instead of traditional unidirectional gradient over the domain scale. Simulations show turbulence throughout the domain, a regime transition to a dominant domain-scale circulation, and a region of logarithmic velocity in the boundary layer. Scaling theory shows a new regime dominated by inertia of the symmetric interior large scale circulation, coupled to thermal dissipation in the boundary layer which explains the Nu ∼ Ra1/4 behaviour.

Finally, I will show circulation in a rotating rectangular basin forced by a surface temperature difference but no wind stress. Here, our focus is on the geostrophic regime for the horizontal circulation with a strong buoyancy forcing (large Ra).

• ## Buoyancy effects on turbulent entrainment

Dominik Krug
University of Melbourne

4pm Friday 6 May 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

In this talk, we will address the question which role buoyancy plays in the entrainment process in unstable configurations such as turbulent plumes. Based on data from direct numerical simulations of a temporal plume we show that the entrainment coefficient can be determined consistently using a global entrainment analysis in an integral framework as well as via a local approach. The latter is based on a study of the local propagation of the turbulent/non-turbulent interface (TNTI) relative to the fluid. We find that locally this process is dominated by small-scale diffusion which is amplified by interface-convolutions such that the total entrained flux is independent of viscosity. Further, we identify a direct buoyancy contribution to entrainment by the baroclinic torque which accounts for 8–12% percent of the entrained flux locally, comparable to the buoyancy contribution at an integral level (15%). It is concluded that the effect of the baroclinic torque is a mechanism which might lead to higher values of the entrainment coefficient in spatial plumes compared to jets. Finally, some results will be presented from applying the local analysis to a stable configuration. Here, buoyancy is observed to reduce the entrainment rate by reducing the surface area of the TNTI and we will consider how this affects the fractal scaling.

• ## Measuring ocean turbulence and inferring ocean mixing

Greg Ivey
University of Western Australia

4pm Friday 29 April 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

• ## Conversion: Experimental factors influencing the quality of PIV results

Kristian Grayson
University of Melbourne

2pm Wednesday 27 April 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Particle Image Velocimetry (PIV) is a useful tool for investigating the behaviour of turbulent flows, enabling the capture of undisturbed instantaneous velocity fields. The shape and alignment of the pulsed laser sheets used in PIV can have a significant impact on the quality of results, where laser profile mismatches can degrade correlation quality. This study develops two key experimental and analysis tools to aid the refinement of PIV techniques and systematically quantify the impact of unoptimised laser characteristics. Improvements to PIV simulation software enable much more experimentally realistic scenarios to be modelled and a laser profiling camera allows laser characteristics and alignment to be quantified in experimental setups for troubleshooting and analysis. The capabilities of these tools can ultimately be used to assess the practicality and possible benefits of more advanced and complex experimental PIV configurations.

• ## Symmetries and symmetry breaking in bluff-body wakes

Justin Leontini
Swinburne University of Technology

4pm Friday 22 April 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

The periodic vortex shedding in the wake of a circular cylinder is one of the most well-studied flows in fluid mechanics. It often serves as a canonical flow for understanding all bluff-body flows, as well as being important in its own right due to the common use of cylindrical cross sections in engineering structures. The periodic forcing on the structure caused by this vortex shedding can lead to large correlated forces and subsequent vibration. Often, it is desirable to control this motion to avoid failure; at other times, this motion may be deliberately amplified to be used as a source of energy harvesting. Here, I will present results looking at simple control strategies of this wake, such as periodic forcing and geometrical modifications such as streamlining. I will show that even these simple modifications to the base cylinder flow can result in significant changes in the flow, and that many of these changes can be understood by considering the interaction of the symmetries of the base flow and the imposed control.

Dr. Justin Leontini joined Swinburne in December 2013. Previous to this, he was an Australian Postdoctoral Fellow at Monash University, spent time working at the Centre for Maths and Information Science at CSIRO, and at l'Institut de la Recherche sur les Phenomenes Hors Equilibre (IRPHE) (trans. Dynamic Systems Research Institute) in Marseille, France. His research work has spanned fundamental fluid-structure interactions, planetary core flows, ship hydrodynamics, and flow stability. Recently, he has been building a project investigating the gas transport mechanisms in specialty ventilation machines in neonatal ICU wards. All of this research is focussed around understanding the fundamental physics of flow phenomena that have relevance to engineering or natural problems.

• ## Direct and large eddy simulations of flows through low-pressure turbines subject to inlet disturbances

Richard Pichler
University of Melbourne

4pm Friday 15 April 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

To reduce specific fuel consumption and cost of jet engines it is desirable to decrease the number of blades. As a result the individual blades of modern low-pressure turbines (LPT) are subjected to more severe pressure gradients that might lead to flow separation. Since laminar boundary layers are more prone to separation than turbulent ones, the actual transition location might dictate if a boundary layer remains attached or not, which in general has a significant effect on losses.

Transition is known to be influenced by the incoming flow state, in particular inlet turbulence and discrete wakes shed by the upstream blade row(s) that in essence are regions of high-turbulence and low-momentum flow. To investigate the interaction of unsteady transition and separation for varying design parameters, a combined large-eddy and direct numerical simulation study has been conducted and the data have been studied in light of loss generation.

• ## The control of near-wall turbulence by non-conventional surfaces

Ricardo García-Mayoral
University of Cambridge | Website

4pm Friday 8 April 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

Complex features on what would otherwise be a smooth wall can alter an overlying turbulent flow. This talk will focus on surfaces that exploit this capability to reduce wall friction, and will discuss three of such surfaces: riblets, permeable and superhydrophobic surfaces. Riblets are a kind of directional roughness made up of small surface grooves aligned in the direction of the flow. Permeable coatings allow the flow to penetrate into the surface to a certain extent. Superhydrophobic surfaces, when immersed in water, can entrap pockets of air, so that the water flow can effectively slip over them. In all cases, for small texture or pore size the reduction of friction increases with size, but beyond a certain size the performance begins to degrade, limiting the range of technological interest and the optimum performance achievable. The talk will discuss both the drag-reducing and the drag-degrading mechanisms for the above three types of surface.

• ## Universality aspects and coupling mechanisms of turbulence

Patrick Bechlars
University of Melbourne

4pm Friday 1 April 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

To understand, describe and model the physical processes that drive a chaotic turbulent flow a comprehensive and detailed understanding of flow features and their interconnection is needed. This can be obtained through a thorough analysis that interprets and breaks down observations across different flows and locations. This should be done to expose key features of turbulence from different points of view. The features then need to be connected to create the solution of the puzzle.

With this in mind a set of detailed time-resolved 3D flow data was sampled. The set involves data from a turbulent boundary layer, turbulent pipe flows, jet flows and a supersonic wake flow. I am happy to share these datasets and look forward to upcoming collaborations.

Besides an outline of the available datasets, some universal and non-universal aspects of turbulence across the different flows will be discussed in the presentation. Further, an analysis based on the velocity gradient invariant is applied to discuss the composition and development of turbulence across a turbulent boundary layer flow. Also, the method was extended to analyze the cascading process of kinetic energy. This analysis exposes the backscatter mechanism that transfers kinetic energy from smaller to larger scales of motion. Results for this will be shown and an underlying physical mechanism will be suggested.

• ## Completion: Structure of mean dynamics and spanwise vorticity in turbulent boundary layers

Caleb Morrill-Winter
University of Melbourne

3.30pm Thursday 24 March 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

• ## 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)

• ## High-fidelity simulations of noise radiation from an elastic trailing-edge

Stefan Schlanderer
University of Melbourne

4pm Friday 11 March 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

• ## 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 aero-acoustics and wall-bounded turbulence

Woutijn Baars
University of Melbourne

4pm Friday 19 February 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

• ## 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 non-axisymmetric bodies of revolution

David Pook
Defence Science and Technology Group

4pm Friday 22 January 2016
Mechanical Engineering Seminar Room Level 3 (Room 311, Bldg 170)

## Postdocs

First nameLast namePrimary supervisorLocation@unimelb.edu.au

## Students

First nameLast namePrimary supervisorLocation@student.unimelb.edu.au
• ## Sea-Ice-Wind-Wave-Interaction facility (SIWI)

Funded by ARC
Contact: Prof Jason Monty | Schedule
• ## Fully resolved measurements of turbulent boundary layer flows up to Reτ = 20,000

Database: Fully_resolved_stats.zip Fully_resolved_spectra.zip
Reference: M. Samie, I. Marusic, N. Hutchins, M. K. Fu, Y. Fan, M. Hultmark & A. J. Smits (2018)
Fully resolved measurements of turbulent boundary layer flows up to Reτ = 20,000.
J. Fluid Mech. 851 391–415 doi:10.1017/jfm.2018.508

• ## A tool to estimate missing energy at a given spatial resolution for turbulent boundary layers

Reference: J. H. Lee, Kevin, J. P. Monty & N. Hutchins (2016)
Validating under-resolved turbulence intensities for PIV experiments in canonical wall-bounded turbulence.
Exp. Fluids 57 129 doi:10.1007/s00348-016-2209-6

• ## Predictive 'Inner-Outer Interaction Model' for turbulent boundary layers

Reference: W. J. Baars, N. Hutchins & I. Marusic (2016)
Spectral stochastic estimation of high-Reynolds-number wall-bounded turbulence for a refined inner-outer interaction model.
Phys. Rev. Fluids 1 054406 doi:10.1103/PhysRevFluids.1.054406

• ## Two-point hot-wire data in a high Reynolds number zero-pressure gradient turbulent boundary layer at Reτ ≈ 15,000

Reference: W. J. Baars, K. M. Talluru, N. Hutchins & I. Marusic (2015)
Wavelet analysis of wall turbulence to study large-scale modulation of small scales.
Exp. Fluids 56 188 doi:10.1007/s00348-015-2058-8

Reference: W. J. Baars, N. Hutchins & I. Marusic (2016)
Spectral stochastic estimation of high-Reynolds-number wall-bounded turbulence for a refined inner-outer interaction model.
Phys. Rev. Fluids 1 054406 doi:10.1103/PhysRevFluids.1.054406

• ## High Reynolds number zero-pressure gradient turbulent boundary layer flow statistics

Reference: I. Marusic, K. Chauhan, V. Kulandaivelu & N. Hutchins (2015)
Evolution of zero-pressure-gradient boundary layers from different tripping conditions.
J. Fluid Mech. 783 379–411 doi:10.1017/jfm.2015.556