**October 28-30, 2021**

Professor Balachandar is currently the William F. Powers Professor in the Department of Mechanical and Aerospace Engineering at the University of Florida. He is the inaugural Director of the Herbert Wertheim College of Engineering Institute for Computational Engineering (ICE) and under his leadership the Institute has established the graduate certificate program in Scientific Computing. He is currently Editor in Chief of the International Journal of Multiphase Flow. His expertise is in computational multiphase flow, direct and large eddy simulations of transitional, turbulent flows, and integrated multiphysics simulations of complex problems. He is a fellow of the American Physical Society and the American Society of Mechanical Engineers. Professor Balachandar received the Francois Naftali Frenkiel Award from the American Physical Society Division of Fluid Dynamics in 1996 and the Arnold O. Beckman Award and the University Scholar Award from the University of Illinois.

The meeting is a part of Complex Systems and Dynamics Group which is an interdisciplinary initiative of Indian Institute of Technology Madras, focussed towards carrying out research on the broad areas involving complex networks and nonlinear dynamics. The aim of the group is to contribute to the development of new techniques and tools for mathematical modelling and analysis to investigate challenging dynamical problems in climate science, neuroscience, biological systems, multi-physics systems and active flows. The centre is envisaged as a hub for promoting interdisciplinary research drawing on expertise and synergy from science, engineering and humanities streams.

The meeting "Multiphase Flows - Advances and Future Directions" is being organized to celebrate the 60th birthday of Professor S. "Bala" Balachandar, honouring his diverse contributions to multiphase flow research. The focus of the meeting is to learn and understand the world of multiphase flow dynamics through research seminars by eminent experts in the field. The shorter format of talks would be by early career researchers, highlighting their latest research in multiphase fluid dynamics. The longer format talks would be more pedagogical, outlining the exceptional problems and providing an overview of possible future directions. Students and starting researchers will get a perspective on the current challenges and the way forward in multiphase flow research through this series of talks.

Registration is free for all but mandatory.

The link for joining the workshop will be sent via email.

Title: Modelling and Computation of Interfaces in Turbulent Multiphase Flows

Abstract:

Droplets carried in turbulent fluids rely, for their existence, on tiny interfaces. Interfaces are not property of the drop or of the the carrier fluid and are inherently a non-place. However, in environmental and industrial processes, their role is enormously important since it is across the interfaces that momentum, heat and mass transfer fluxes coupling the drop to the carrier fluid occur: the accurate determination of their position, shape and interaction with the fluid turbulence is crucial to predict physical phenomena, and industrial and environmental processes. To this aim, Direct Numerical Simulation (DNS) of turbulence and accurate tracking of the interface are required, but the range of scales involved for most of practical environmental and industrial applications is so wide that performing this task is a formidable challenge for present day computers: The grid resolution for DNS of turbulence is of the order of the Kolmogorov scale, but of course physical interfaces have a much smaller scale (order of few molecules) making the direct resolution unfeasible.

In this talk, we will briefly review the current computational methodologies used to interfaces and the we will focus on the phase-field approach in turbulent flows: In this Eulerian approch, the phase distribution is described by the order parameter φ. We will examine several flow instances and phenomena ranging from turbulent stratified flows to turbulent dispersion of drops and bubbles so to reveal potentials and limitations of the phase-field method. Interface interactions with turbulence, coalescence and breakup phenomena for different values of fluids density and viscosity will be discussed in connection with the characteristics of turbulence. Finally, the physics modelling and the method required to include the effect of surfactants will also be examined.

Bio:

Alfredo Soldati is a Professor and the head of the Institute of Fluid Mechanics and Heat Transfer at TU Wien, Austria. He is currently an Editor-in-Chief of the International Journal of Multiphase Flow and serves as a member of the Editorial Advisory Board of Physics of Fluids. His research focuses on turbulent multiphase flow with environmental and industrial applications.

Title: Two Problems on the Flow of Thin Films

Abstract:

This presentation will focus on two aspects of the flow of thin film on solid surfaces. The first one is the flow of a film ”hanging” on the underside of an inclined plane. Aside from applications to situations such as vapor condensation, this problem is scientifically interesting due to the competition between the Rayleigh-Taylor instability, which would lead to dripping, and the Kapitza instability, which causes waves to emerge from the surface of the film. It is found that, when the inclination of the plate is slowly changed, the transition from Kapitza- to Rayleigh-Taylor-dominance occurs via an unexpected quasi-equilibrium process. The system also exhibits a very strong dependence on initial conditions, with one or the other instability in dependence of the amplitude of the initial disturbance and other factors. The second problem considers the hydraulic jump on the upper surface of a downward oriented cone, including the case of a plane as a special case. It is shown that, as the aperture of the cone is decreased below 90◦ (i.e., a plane), the hydraulic jump disappears and is replaced by the axi-symmetric equivalent of a Nusselt film flow. When the cone aperture is small enough, the axi-symmetric Kapitza-like waves appear which, however, are gradually damped by the geometry of cone surface.

Bio:

Following his departure from the Johns Hopkins University after several decades of service as C.A. Miller Jr. Professor of Mechanical Engineering, Andrea Prosperetti is currently a Distinguished Professor of Mechanical Engineering at the University of Houston, with a part-time appointment as Berkhoff Professor of Applied Physics at the University of Twente in the Netherlands. Prosperetti’s scientific interests center on multiphase flow, with a particular focus on bubble dynamics, averaged equations and resolved simulations of particulate flows. He has been Editor in Chief of the International Journal of Multiphase Flow from 2007 to 2017 and has authored/co-authored over 250 journal papers and two books.

Title: Convective flows with boiling and icing boundaries

Abstract:

In this talk, I will discuss two problems. The first problem is about convective flow with boiling boundary. We have conceptualized a kind of “active particle” turbulence, which far exceeds the limits of classical thermal turbulence. By adding a minute concentration of a heavy liquid (hydrofluoroether) to a water-based turbulent convection system, a remarkably efficient biphasic dynamics is born. We find that the heat transfer enhancement is dominated by the kinematics of the active elements and their induced-agitation. The second problem is about convective flow coupled with solidification or melting in water bodies. We investigate solidification of freshwater, properly considering phase transition, water density anomaly, and real physical properties of ice and water phases, which we show to be essential for correctly predicting the different qualitative and quantitative behaviors. We identify, with increasing thermal driving, four distinct flow-dynamics regimes, where different levels of coupling among ice front and stably and unstably stratified water layers occur. Despite the complex interaction between the ice front and fluid motions, remarkably, the average ice thickness and growth rate can be well captured with a theoretical model.

Bio:

Chao Sun is a professor at the Center for Combustion Energy, Tsinghua University, Beijing, China. He is an associate editor of the International Journal of Multiphase Flow, an editor of Journal of Turbulence, and serves on the editorial board member of Physical Review Fluids. His research interests are in multiphase flows, high Reynolds number turbulence and microfluidics.

Title: Falling clouds of particles in vortical flows

Abstract:

The settling of a cloud of solid spherical particles through vortical structures is examined. The key question is whether this cloud maintains a cohesive entity or disintegrates and spreads when settling through this complex flow structure. The present work considers a simple vortical flow, specifically a cellular flow consisting of counter-rotating vortices, which is a model flow capturing key features of vortical effects on the particles. It addresses the interplay between the multibody particle interactions and the interaction between the particles and the spatial structures of the flow. The focus is on flow regimes ranging for negligible to small but finite inertia but at low Stokes numbers.

Reference:Bio:

Élisabeth Guazzelli is the director of research for the French National Centre for Scientific Research (CNRS), affiliated with the Laboratoire Matière et Systèmes Complexes at the University of Paris. She is an editor of the Journal of Fluid Mechanics Rapids. She is known for her work in the field of particulate multiphase flows, such as granular media, fluidized beds, suspensions, and sedimentation.

Title: Dilute Suspension Rheology

Abstract:

I will discuss the rheology of suspensions in the dilute regime corresponding to small particle volume fractions. The focus will be on the rheological indeterminacy that prevails in the Stokesian limit, in the absence of stochastic fluctuations (Brownian motion), and that makes the rheological calculation a subtle and a difficult one even in the dilute limit. I will explain the idea of rheological indeterminacy in the context first analyzed by Batchelor and coworkers - a Stokesian spherical particle suspension, with pairwise hydrodynamic interactions, in simple shear flow. I will also discuss dilute suspensions of anisotropic particles where one already encounters a rheological indeterminacy in the absence of interactions. Weak non-hydrodynamic effects, the examples of which include Brownian motion, short-range repulsive forces and inertia, can play important roles in resolving the indeterminacy, and thereby affect the suspension rheology in a singular manner.

Bio:

Ganesh Subramanian is a Professor at the Engineering Mechanics Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India. His research focusses on microhydrodynamics, active matter, hydrodynamic stability, particle motion in stratified fluids and complex fluids.

Title: Role of gas cushion during the impact of a drop: regimes and energetics

Abstract:

Tiny drops of millimetre size are known to bounce on a solid surface if the surface is superhydrophobic. If the surface is hydrophobic, either complete or partial rebound usually occurs. Recent experiments show that bouncing can occur even on hydrophilic surfaces under conditions where the drop is supported on a thin cushion of gas preventing it from making contact with the surface. We present a detailed insight into this observation by simulating bouncing dynamics of a drop on a flat solid surface using axisymmetric direct numerical simulations. The shape of the gas profile beneath the drop significantly varies with both Reynolds and Weber numbers. A number of scaling laws are derived for various geometrical parameters of the drop and the gas cushion. We also examine the role of the gas cushion in dissipating the impact force via a detailed energy budget for one bouncing cycle. For higher Weber and Reynolds numbers, a bouncing drop captures a gas bubble inside it consistent with simple experiments carried out for water drops bouncing on superhydrophobic surfaces. We show that a large amount of dissipation occurs during bubble entrapment and escape process. Finally, analysis of the flow field in the underlying gas layer reveals that maximum dissipation occurs in this layer and a simple scaling law is derived for dissipation that occurs during impact.

Bio:

Harish Dixit is an Associate Professor in the Department of Mechanical and Aerospace Engineering, Indian Institute of Technology Hyderabad, India. His research interests are in dynamics of drops and bubbles, thin films and vortex dynamics.

Title: Flow Modulation by Heavy Inertial Particles

Abstract:

It is well established that inertial particles dispersed in turbulent or vortical flows tend to deviate from the carrier flow streamlines. This results in complex particle distribution which includes the formation of concentrated particle clusters, caustics, as well as as large region of space devoid of particles. However, much is less known on how inertial particles alter the suspending flow. For heavy inertial particles, as typically found in gas-solid flows, particle volume fraction as low as 10-5 is sufficient to modulate the carrier flow significantly. In this talk, I will show how small inertial particles selectively modulate flow structures, the mechanisms controlling the modulation, and possible applications in flow control. In simulations of particle-laden homogeneously sheared turbulence, I show that injecting heavy inertial particles results in augmentation or attenuation of turbulence depending on the particle properties. It is found that particle inertia, quantified by the Stokes number, controls the type of modulation (augmentation vs attenuation) obtained whereas increasing mass loading serves to amplify these effects. I propose a mechanism for turbulence attenuation based on the collective interaction of particles with vortex tubes. In simulations of an isolated particle-laden vortex tube, I show that the clustering of particles into rings causes a significant attenuation of the vortex and provide estimates for the time and length scales involved. Finally, I show that the modulating effect of such inertial particles can be leveraged in flow control. I illustrate this aspect in simulations of turbulent channel flows, where I show that it is possible to achieve skin-friction drag reduction to a significant level through injection of carefully selected particles.

Bio:

Houssem Kasbaoui is an Assistant Professor in the School for Engineering of Matter, Transport and Energy, Arizona State University, USA. His research interests include massively parallel simulations of multiphase and aerosol-laden flows for environmental and aerospace applications.

Title: Interplay of a pair of rising bubbles released in line

Abstract:

Highly resolved simulations are used to analyse the buoyancy-driven motion of two gas bubbles released in line in a liquid at rest, focusing on regimes in which the path of an isolated bubble is vertical.

We first constrain the evolution to remain axisymmetric and determine the equilibrium congurations of the bubble pair as a function of the two control parameters of the system, namely the buoyancy-to-viscous and buoyancy-to-capillary force ratios defining the Galilei (Ga) and Bond (Bo) numbers of the system, respectively. However the three-dimensional solutions reveal that this axisymmetric equilibrium is actually never reached. At the lower end of the explored (Ga, Bo)-range, the bubble pair follows a Drafting-Kissing-Tumbling scenario

which eventually yields a planar side-by-side motion. For larger Ga, the trailing bubble drifts laterally and gets out of the wake of the leading bubble, barely altering the path of the latter. In this second scenario, the late conguration is characterized by a signicant inclination of the tandem. Last, when the Bond number exceeds a critical Ga-dependent threshold, the two bubbles get very close to each other and eventually coalesce. The simulations reveal that bubble deformation has a major influence on the evolution of the system. It controls the strength of the leading bubble wake, hence that of the attractive force acting on the trailing bubble. It also governs the strength and even the sign of the lateral force acting on this bubble, a mechanism of particular importance when the bubble pair is released with a small angular deviation.

Bio:

Jacques Magnaudet is a Senior Researcher at CNRS (the French National Center for Scientific Research), working at the Fluid Mechanics Institute of Toulouse (IMFT). He is currently an associate editor of the Journal of Fluid Mechanics and the International Journal of Multiphase Flow. His research focusses on several fundamental aspects of hydrodynamics and turbulence in two-phase flows and inhomogeneous fluids, mostly studied by means of computational and theoretical approaches.

Title: Polymer scission in turbulent flows

Abstract:

Polymers in a turbulent flow experience strong, intermittent, fluctuating strain-rates, and thus undergo significant stretching. The resulting feedback onto the flow is known to dramatically reduce turbulent drag in channel flows (or kinetic energy dissipation in homogeneous flows). However, the same intense stretching also leads to the mechanical scission of polymers and a reduction in the mean molecular mass, thereby limiting the experimental study and application of drag/dissipation reduction. In this study, we analyse polymer scission in homogeneous isotropic turbulence, using a combination of stochastic modelling and Eulerian-Lagrangian direct numerical simulations (DNS). We obtain analytical predictions for the first scission event, including the breakup rate and survival time statistics, which agree well with DNS. By accounting for the feedback of polymers onto the flow, we show how scission leads to the loss of the dissipation-reduction effect. Indeed, we show that the overall dissipation-reduction is maximised by an intermediate polymer relaxation time, for which polymers stretch significantly but without breaking too quickly. We also study the dynamics of the polymer fragments which form after scission; these daughter polymers can themselves undergo subsequent repeated breakups, to produce a hierarchical population of polymers with a range of relaxation times and scission rates.

Bio:

Jason R. Picardo is an Assistant Professor in the Indian Institute of Technology Bombay, India. His research interests are on complex viscous flows, turbulent transport of particles, polymers and filaments and instabilities and pattern formation in fluid flows.

Title: Challenges and opportunities in modeling high-speed gas-particle flows

Abstract:

While the past several decades have seen significant progress in developing predictive modeling capabilities for disperse two-phase flows, the majority of these efforts have focused on dilute suspensions of particles under low-speed (incompressible) conditions. This talk will focus on recent progress towards understanding and predicting particle-laden flows in more extreme environments, in which gas-phase compressibility and back-coupling from particles to the fluid have an order-one effect. Some relevant examples include solid propellant combustion, coal dust explosions, volcanic eruptions, and plume-surface interactions during planetary/lunar landing. I will present an overview of existing models, with origins from 18th-century cannon fire experiments and new insights from particle-resolved numerical simulations.

Bio:

Jesse Capecelatro is an Assistant Professor in the Department of Mechanical Engineering at the University of Michigan, Ann Arbor. His research group develops numerical methods and data-driven approaches for the prediction and optimization of "messy turbulent flows" relevant to energy and the environment (often multiphase and reacting).

Title: The bubble size distribution under breaking waves: fundamental scalings and implications

Abstract:

Breaking waves at the water surface is a striking example of turbulent mixing across a fluid interface. The impact of the jet generates turbulence, entrains air into the water and ejects droplets into the air. A fundamental understanding of the general multi-scale properties of the resulting air-water turbulent flow is necessary to develop more accurate gas transfer or spray generation parameterizations. I will discuss air entrainment and bubble statistics under a breaking wave, using a combination of direct numerical studies and laboratory experiments to describe the bubble size distribution in a turbulent flow. For bubbles larger than the Hinze scale, the distribution can be described by a turbulent break-up argument, while below the Hinze scale, rapid capillary break-ups of the large bubbles are responsible for the observed scaling law of the distribution. The implications of the breaking dynamics on air-sea mass transfer, in particular the gas transfer and sea spray aerosol generation by bubble bursting will be discussed.

Bio:

Luc Deike is an Assistant Professor at Princeton University, in the Mechanical and Aerospace Engineering Department and the High Meadows Environmental Institute. His research interests include breaking waves, bubble dynamics in turbulence and gas transfer, as well as bubble bursting and spray generation.

Title: Investigating turbulent particulate flows with the aid of invariant solutions

Abstract:

Turbulent particulate flows exhibit a multitude of phenomena with significant practical consequences. An example is the often observed heterogeneous spatial distribution of the disperse phase which impacts a range of systems, from cloud micro-physics to chemical engineering devices. For idealized configurations, precise data on both phases can now routinely be generated by means of particle-resolved DNS. However, it is still an arduous task to extract the salient physics directly from the turbulent fields. Here we are exploring the idea of simplifying the carrier-phase flow by resorting to invariant solutions to the Navier-Stokes equations. We will discuss the feasibility of tracking the motion of finite-size particles in such fields and their stability by way of examples in wall-bounded and unbounded configurations.

Bio:

Markus Uhlmann is a Professor, Joint Head of the Institute and Head of the CFD group at Karlsruhe Institute of Technology, Karlsruhe, Germany.

He is currently a member of the Editorial Board of International Journal of Multiphase Flow, Editorial Board of Flow, Turbulence & Combustion and Steering committee of the computer centre HLRS. His research interests are dynamics of coherent structures in turbulent flows, multi-phase flows, numerical simulation techniques and high-performance computing.

Title: Surface tension as a destabilizer in 2D

Abstract:

Normally we expect surface tension to stabilise short wavelength disturbances on interfaces and do little to long waves. We ask if anything different can happen in 2D turbulence in multiphase flow. We first study a single vortex at an initially flat interface as a building block of such turbulence. This flow goes unstable due to surface tension, and we will discuss why. Secondly, when there is a density difference between the fluids on either side of the interface, a Centrifugal Rayleigh-Taylor and a "Spiral Kelvin Helmholtz" instability ensue. We find signatures of these instabilities in 2D turbulence.

Bio:

Rama Govindarajan is a Professor at the International Center for Theoretical Sciences-TIFR, Bangalore, India. She is currently a member of Editorial Board, Physical Review Fluids. She is known for her work on flow instabilities, cloud fluid dynamics and the combined dynamics of deformable solids and fluids.

Title: Dimple and jet formation in nonlinear surface waves

Abstract: To be announced soon

Bio:

Ratul Dasgupta is an Associate Professor in the Chemical Engineering Department at Indian Institute of Technology Bombay, India. His research group studies single and multi-phase fluid problems in the laminar and turbulent regimes inspired by interesting phenomena involving waves and oscillations, in the atmospheric & oceanic sciences along with some engineering problems.

Title: Bubbles and drinks

Abstract:

In this talk we show some of our recent results conducted in the most common multiphase flow laboratory: you glass of bubbly drink. Most people find bubbly drinks to be attractive and refreshing. With the excuse of trying to answer why, we explore the physics involved in this particular kind of two-phase, mass-transfer-driven flow. Discussion and analysis of the processes of bubble formation, ascension, accumulation and bursting are presented. Links to other relevant flow phenomena are presented in each case.

Bio:

Roberto Zenit is a Professor at the School of Engineering at Brown University, Providence, USA. He is currently an associate editor of Physical Review Fluids and International Journal of Multiphase Flow. His group conduct research in the following areas: the mechanics of Two-Phase Flows, Non Newtonian Fluid Mechanics, Fluid Mechanics of Painting and Biological Flows.

Title: A unified theory of multiphase turbulence

Abstract:

A theory of multiphase turbulence is formulated on the basis of fluctuations of filtered fields about their ensemble average, which were recently introduced (Subramaniam 2020, Phys. Rev. Fluids 5, 110520). Turbulent multiphase flows are intrinsically multiscale phenomena that are broadly classified as microscale (on the scale of a particle, droplet or bubble), mesoscale (on the scale of ten to hundred particle diameters), and macroscale (scale of the device). Fluctuations in particle or fluid quantities can arise from the initial random configuration of the particles and state of the fluid, or from non-random sources that represent spatial variation on scales smaller than the scale on which the multiphase flow is characterized. A single--point theory is desirable for ease of modeling unclosed terms and simulation, but two--point statistics are indispensable to characterize fluctuations in particle and fluid volume fraction. These three features of multiphase turbulence make its theoretical treatment uniquely challenging, and have not been satisfactorily addressed by previous theories. This new formulation possesses several advantages that allow it to address all these challenges, thereby overcoming key limitations in previous theories. The principal advantage of this theory is that it is based on fluctuations of filtered fields that contain local spatio-temporal information, which can be related to two--point statistical information. Reconcilability with representations at micro, meso and macroscales is guaranteed in a rigorous manner at the single--point level of closure. This theoretical framework reduces to the classical two-fluid theory in the appropriate limit, and serves to unify the seemingly disparate theoretical approaches to multiphase turbulence proposed by Fox and Sundaresan.

Bio:

Shankar Subramaniam is a Professor in the Department of Mechanical Engineering at Iowa State University. He is Founding Director of CoMFRE: Multiphase Flow Research and Education. He has served on the editorial board of the journal Atomization and Sprays and International Journal of Spray and Combustion Dynamics. His areas of expertise are in theory, modeling and simulation of multiphase flows (including sprays, particle-laden flows, colloids and granular mixtures), turbulence, mixing, and reacting flows.

Title: Shear Induced Lift Force and Bubble Clustering Phenomenon

Abstract:

It is well-known that small amounts of surfactant can drastically change the behaviors of rising bubbles. For example, a bubble in aqueous surfactant solution rises much slower than one in purified water. This phenomenon is explained by the so-called Marangoni effect caused by a nonuniform concentration distribution of surfactant along the bubble surface. In other words, a tangential shear stress appears on the bubble surface due to the surface tension variation caused by the surface concentration distribution, which results in the reduction of the rising velocity of the bubble. More interestingly, this Marangoni effect influences not only the rising velocity, but also the lateral migration in the presence of mean shear. That is, the lift force acting on a 1mm-sized bubble due to the presence of the mean shear is well-predicted by Legendre and Magnaudet (1995) for super-purified system and also well-predicted by the Bagchi and Balachandar (2002) for fully contaminated system. This difference of lift force causes the drastic change to the occurence of bubble clustering phenomena. Furthermore, these phenomena influence the multiscale nature of bubbly flows and cause a drastic change in the turbulent flow structure. In the present talk, these interesting multiscale structures will be explained in detail.

Bio:

Shu Takagi is a Professor at Department of Mechanical Engineering, School of Engineering, The University of Tokyo. He is currently an associate editor of International Journal of Multiphase Flow. His research interests are Human Body Simulator for the Next Generation Super Computer, Microbubbles and Nanobubbles, Numerical Analysis of Moving Boundary Problems, Multiscale Analysis of Multiphase Flows, Nano-Scale Themo-Fluid Mechanics, Medical Applications of Thermo-Fluid Mechanics.

Title: Suspension dynamics: from accumulation to fingering

Abstract:

When the mixture of viscous oil and non-colloidal particles displace air between two parallel plates, the shear-induced migration of particles leads to the gradual accumulation of particles on the advancing oil-air interface. This particle accumulation results in the fingering of an otherwise stable fluid-fluid interface. While our previous works have focused on the resultant fingering phenomenon, one unexplored yet striking feature of the experiments is the self-similarity in the concentration profile of the accumulating particles. In this talk, we model the system mathematically by considering the depth-averaged particle transport equation and suspension balance model. The solutions to the particle transport equation are shown to be self-similar with slight deviations, and in excellent agreement with experimental observations. Our results demonstrate that the combination of the shear-induced migration, the advancing fluid–fluid interface and Taylor dispersion yield the self-similar and gradual accumulation of particles

ReferenceBio:

Sungyon Lee is an Associate Professor in the Mechanical Engineering Department at University of Minnesota. She is a fluid mechanician who specializes in uncovering the fundamental physical mechanisms behind complex phenomena at fluid-fluid interfaces. She combines flow visualization experiments and mathematical modeling to investigate diverse problems that range from drops and bubbles, particle-laden flows, particle rafts, to two-phase flows through porous media.

Title: Turbulence collapse in a dilute particle-gas suspension

Abstract: To be announced soon

Bio:

Viswanathan Kumaran is a Professor in the Department of Chemical Engineering at Indian Institute of Science, Bengaluru, India. He is currently a member of Editorial Board, Physical Review Fluids and

an associate editors of International Journal of Multiphase Flow. His work is focused on complex flows of complex fluids, and he is known to have carried out theoretical and experimental research on the stability of flow past flexible surfaces.

Title: Direct Numerical Simulations of bubbly flows: statistics

Abstract:

Thanks to the increasing computation power and adaptive grid refinement, we perform direct numerical simulations of a three-dimensional bubble column with a volume-of-fluid method. Such highly resolved simulations provide us detailed information/data to better understand the bubble dynamics. Unlike many reported study, our studied bubbly column case involves large number of bubbles at high Re with both bubble-induced-turbulence and shear-induced-turbulence present. We analyzed the simulation results from a statistical point of view. The statistics explain 1) how the bubbles are organized within the swarm and 2) why bubbles are dispersed laterally.

Bio:

Yali Tang is an Assistant Professor at the Power and Flow group in the Department of Mechanical Engineering at Eindhoven University of Technology (TU/e). Her research expertise focuses on the fundamentals of multiphase flows using computational fluid dynamics modelling. An important research topic is the hydrodynamics, mass and heat transfer in fluid-particle systems such as in packed and fluidized beds, as well as bubble column reactors.

Title: Effect of inlet gas turbulence on gas-liquid interfacial instability and airblast atomization.

Abstract:

In airblast atomization, the breakup of a liquid jet is assisted by a parallel high-speed gas stream. Detailed interface-resolved simulation is performed to investigate the effect of inlet gas turbulence on airblast atomization. Due to the velocity difference between the two streams, the shear on the interface triggers a longitudinal instability, which initiates the destabilization of the liquid jet. Depending on the injection and geometric conditions, the longitudinal instability can be convective and absolute. In the absolute instability regime, the most-unstable mode determines the frequency and wavelength of the longitudinal waves formed on the jet interface. The vertical interfacial motion induced by the longitudinal shear instability triggers the transverse Rayleigh-Taylor (RT) instability. As a result, as the longitudinal wave grows spatially, transverse modulations arise, turning the interfacial wave from quasi-2D to fully 3D. The inlet gas turbulence is shown to have a strong impact on the longitudinal instability. The dominant frequency and the spatial growth rate both increase with the inlet gas turbulence intensity. Since the transverse instability is closely connected to the longitudinal counterpart, the dominant transverse wave number also increases with the inlet gas turbulence intensity. An estimate of the dominant transverse wavenumber is made based on the RT theory, which scales with the longitudinal frequency. The theoretical predictions are in good agreement with simulation results. Finally, the sheet breakup dynamics, the statistics of the droplets and turbulence are also discussed.

Bio:

Yue (Stanley) Ling is an Assistant Professor in the department of Mechanical Engineering at the School of Engineering and Computer Science, Baylor University, Waco, Texas. His research interests are Multiphase flows; atomization and sprays; microfluidics, particle-laden flows, shock/detonation waves, high-performance computing.

Title: Challenges and opportunities in modeling high-speed gas-particle flows

Title: Investigating turbulent particulate flows with the aid of invariant solutions

Title: The bubble size distribution under breaking waves: fundamental scalings and implications

Title: Effect of inlet gas turbulence on gas-liquid interfacial instability and airblast atomization

Title: Role of gas cushion during the impact of a drop: regimes and energetics

Title: Modelling and Computation of Interfaces in Turbulent Multiphase Flows

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