This event commemorates the life and work of George Batchelor (1920 – 2000). George was a towering figure in the field of fluid mechanics, carrying out ground-breaking research on turbulence and then on micro-hydrodynamics. In addition to his personal research, George established the DAMTP where this meeting is being held. DAMTP has trained many prominent researchers in fluid mechanics from the UK and around the world and hosted many academic visitors working in the subject.
Globally, George founded the Journal of Fluid Mechanics, arguably the most highly-regarded and influential journal in the field that is read by scholars world-wide. He also fostered international collaboration by being one of the founders of EUROMECH and he played a prominent role in IUTAM, both of which are sponsoring this meeting along with Cambridge University Press. He also took personal leads in establishing contact with scientists behind the Iron Curtain and with China once relations softened at the end of the Cultural Revolution.
In honour of the Centenary, a Special Volume of JFM has been published in tribute to George Batchelor. All papers in this volume are free to read in perpetuity and we invite you to read and share.
This meeting, sponsored by EUROMECH, IUTAM, Cambridge University Press and Trinity College celebrates these achievements by bringing together invited speakers: the three previous Batchelor Prize winners, Howard Stone (Princeton, USA), Detlef Lohse (Twente, Netherlands) and Ray Goldstein (Cambridge, UK), and plenary lectures from Berengere Dubrulle (SPEC, Saclay, France), Rama Govindarajan (ICTS, Bengaluru, India) and Xiaojing Zheng (Lanzhou, China).
Programme:
Monday 29th March
1230 Welcome
1300 Ray Goldstein: Two stories of fluids and light: algal phototaxis and dinoflagellate bioluminescence
1400 Rama Govindarajan: Stratified viscosity: a singular and nonlinear tale
Tuesday 30th March
1230 Patrick Huerre: George Batchelor and the founding of EUROMECH
1300 Detlef Lohse: Physicochemical hydrodynamics of droplets and bubbles out of equilibrium
1400 Berengere Dubrulle: On the small scale structure of turbulence
Wednesday 31st March
1230 Xiaojing Zheng: Turbulence effects in wind-blown sand movements
1330 Howard Stone: Modern applications of classical ideas in fluid mechanics: thin films, physical chemistry and molecular biology
1430 Keith Moffatt: George Batchelor - a personal reminiscence
Welcome
Welcome and introductions by Professor Paul Linden, Professor Colm Caulfield, Professor Grae Worster, Professor Juan Santiago, Professor Beverley McKeon.
Two stories of fluids and light: algal phototaxis and dinoflagellate bioluminescence
Raymond E. Goldstein FRS is the Schlumberger Professor of Complex Physical Systems at the University of Cambridge, and Fellow Churchill College, Cambridge. His PhD on aspects of phase transitions and critical phenomena 83/88 was under the direction of Neil Ashcroft at Cornell University. His research since then has focused on nonlinear dynamics, pattern formation, and biological physics, combining both theory and experiment. He is best known for studies of active matter, including the fluid mechanics of microorganism motility, collective behaviour, and synchronisation of flagella, as well as explanations for natural patterns such as stalactites, icicles, and ponytails.
Abstract: This talk focuses on two examples of phenomena involving microorganisms and light.
The first concerns the dynamics of phototaxis - directed motion towards light - exhibited by green algae. This occurs without a central nervous system, driven solely by the response of individual cells, and all such algae spin about a body-fixed axis as they swim; directional photosensors on each cell thus receive periodic signals when that axis is not aligned with the light. Our studies of unicellular Chlamydomonas, the small organism Gonium (16 cells), and much larger Volvox (~1000 cells) reveal a common adaptive response to such signals with a tuning between the adaptation time scale and the orbital period of the colony that enables phototaxis with high fidelity.
The second example involves light production. One of the characteristic features of many marine dinoflagellates is their bioluminescence, which lights up night-time breaking waves or seawater sliced by a ship's prow. While the internal biochemistry of light production is well established, the manner by which fluid shear or mechanical forces trigger bioluminescence is still poorly understood. I will describe controlled measurements of the relation between mechanical stress and light production at the single-cell level, using high-speed imaging of micropipette-held cells of the marine dinoflagellate Pyrocystis lunula subjected to localized fluid flows or direct indentation. We find a viscoelastic response in which light intensity depends on both the amplitude and rate of deformation, consistent with the action of stretch-activated ion channels. A phenomenological model captures the experimental observations.
Click here to access a relevant JFM paper in support of Goldstein's talk.
Stratified viscosity: a singular and nonlinear tale
Rama Govindarajan is a Senior Professor at the International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bengaluru. PhD from the Indian Institute of Science and was a Postdoctoral Fellow at CalTech. She is on the Editorial Board of Physical Review Fluids and Divisional Associate Editor of the Physical Review Letters. She has worked extensively on flow instabilities, and her recent interests are in particulate turbulence and in cloud flows. She likes making connections between pen and paper physics and computational results.
Abstract: This talk will address the profound and unexpected ways in which viscosity variations can affect shear flow. The most striking manifestations are through alterations of flow stability. Viscosity variation appears as a singular perturbation in the linear stability operator of shear flows. Due to this, a minor stratification of viscosity can produce a large change in the stability properties: a ten percent change across a carefully placed thin mixed layer in a channel can change the instability-critical Reynolds number by an order of magnitude. I will then describe our recent work on the early stages of perturbation growth in channel flow (Thakur, Sharma & Govindarajan 2021, J Fluid Mech., Batchelor Centenary Issue). The viscosity varies across the channel due to differential heating at the walls. We derive the viscosity-varying adjoint Navier-Stokes equations, and by the technique of direct-adjoint looping, obtain the nonlinear optimal perturbation which maximises the perturbation kinetic energy. Nonlinearity is shown to be important throughout and a modified lift-up mechanism is in operation. The process is strongly asymmetric, initially focussed on the hot side and then shifting to the cold side, where high-speed streaks of low viscosity grow and persist. I hope to convince the audience that studying the transition to turbulence in such flows would be a worthwhile pursuit.
George Batchelor and the founding of EUROMECH
Patrick Huerre is a member of the Académie des sciences and Emeritus Director of research in the Hydrodynamics laboratory of Ecole Polytechnique. He served as President of Euromech, the society founded by George Batchelor and Dietrich Küchemann in the sixties. His major contributions include the effective use of absolute/convective instability concepts to distinguish between flow amplifiers and oscillators, the introduction of linear and nonlinear global modes to account for the dynamics of oscillators and the identification of super-directivity in aerodynamic sound generation. He currently studies the structure of critical layers in astrophysical proto-planetary disks.
Abstract: The lecture shows how George Batchelor, in close collaboration with Dietrich Küchemann, succeeded in founding Euromech, the European Mechanics Committee, in the sixties during the rise of the “Cold War”. The initial success of Euromech was due to the organisation of colloquia, i.e. meetings of about 50 scientists, focussing on a sufficiently specialized topic and leaving ample time for informal discussions. The maturation of the Euromech committee into the European Mechanics Society in the nineties, initiated by David Crighton and Hans Fernholz is then analyzed. This transition was in part made necessary by the creation of five series of large European Conferences in Fluid and Solid Mechanics, Turbulence, Nonlinear Oscillations and Mechanics of Materials. In the last two decades, the visibility of Euromech in the scientific community has been further enhanced by the introduction of three types of distinctions : the status of Honorary Member for exceptional service, Fluid and Solid Mechanics prizes for life-time contributions and the status of Euromech Fellow for significant contributions. For almost sixty years the collective action of George Batchelor and a few outstanding European scientists has proved to be essential to the success of Euromech as a leading society in the field of Mechanics.
Physicochemical hydrodynamics of droplets and bubbles out of equilibrium
Detlef Lohse got his PhD at the University of Marburg, Germany, in 1992, on fully developed turbulence. After some time as a postdoc in Chicago and again in Marburg, in 1998 he became Chair of Physics of Fluids at the University of Twente in the Netherlands, where he as been ever since. He is also a Member of the Max Planck Society and of the Max-Planck Institute in Göttingen. His present research focus is on turbulence, thermal convection, multiphase flow, and on micro- and nano-fluidics (bubbles, drops, inkjet printing, wetting). He and his group do both fundamental and more applied science.
Abstract: The physicochemical hydrodynamics of droplets and bubbles out of equilibrium, in particular with phase transitions, display surprisingly rich and often counter-intuitive phenomena. In this talk I will present two prototypical examples.
First, I will show that a silicone oil drop immersed in a stably stratified ethanol-water mixture can continuously bounce up and down (with frequencies of ~1/50 Hz), if it is large enough. Smaller droplets are suspended by the Marangoni flow, which levitates the drop against gravity above its neutral density point. The transition from levitating to bouncing reveals an instability of the equilibrium between the Marangoni flow and gravity. The onset of this instability occurs when the Marangoni advection is too strong for diffusion to restore the stably stratified concentration field around the drop.
In the second example I will discuss the nucleation and early evolution of plasmonic bubbles in a binary liquid consisting of water and ethanol. Remarkably, the plasmonic nanobubble is found to be periodically attracted to and repelled from the nanoparticle-decorated substrate, with frequencies of around a few kHz. The competition between solutal and thermal Marangoni forces is the origin of the periodic bouncing. The former arises due to the selective vaporization of ethanol at the substrate’s side of the bubble, leading to a solutal Marangoni flow towards the substrate, which pushes the bubble away. The latter arises due to the temperature gradient across the bubble, leading to a thermal Marangoni flow away from the substrate which sucks the bubble towards it.
Enjoy free access to papers in support of Lohse's talk, courtesy of the Journal of Fluid Mechanics.
On the small scale structure of turbulence
Berengere Dubrulle is senior scientist at the Centre National de la Recherche Scientifique and presently Director of the Les Houches Physics School. She received her PhD in astrophysics in 1990 under the supervision of J-P. Zahn. She is a specialist of turbulence, and its application to astro and geophysical flows using theoretical, numerical or experimental approaches. Her major achievements concern theory of the solar system formation, statistical modelling of large scales and their bifurcations, or mathematical aspects of the small scale structure, in connection with singularities and intermittency. She was involved in the VKS dynamo experiment and in the SHREK superfluid (quantum) turbulence experiment.
Abstract: In 1949, Batchelor and Townsend published the first experimental account about inconsistencies in the original 1941 Kolmogorov turbulence theory. Observing the increase with Reynolds number of the flatness of the distribution of velocity derivatives, they conjectured a highly inhomogeneous distribution of vorticity at small scale, thereby providing a clear scenario of building of intermittency at the dissipative scales. In the same time, Batchelor also got interested in a singular stationary solution of Navier-Stokes first found by Landau in 1944.
In this talk, I revisit the path and thoughts of G.K. Batchelor to draw a modern picture of the small scales of turbulence using data form recent numerical simulation and laboratory experiments. I first discuss how intermittency is generated at the location of extreme events of local energy transfer in the dissipative range and characterize the velocity field as these locations. I show that such intense events are associated with reconnection events, produced by interacting Burgers vortices.
I discuss the possible theoretical models of such interaction and introduce a model of interacting singularities of Navier-Stokes, named pinçons, that generalize Landau solutions. They follow a Hamiltonian dynamics. When immersed in a regular field, the pinçons are further transported and sheared by the regular field, while applying a stress onto the regular field, that becomes dominant at a scale smaller than the Kolmogorov length. This provides a general two-fluid model of the turbulence, valid for all scales down to the deep dissipative range.
Work done in collaboration with the EXPLOIT* team and F. Nguyen, H. Faller and D. Geneste. (* T. Chaabo, A. Cheminet, V. Valori, Y. Ostovan, L. Cappanera, Ch. Cuvier , F. Daviaud, J.-M. Foucaut, J.-L. Guermond, J.-Ph. Laval, C. Nore, V. Padilla, C.~Wiertel.)
Turbulence effects in wind-blown sand movements
Xiaojing Zheng took her PhD on Mechanics at Lanzhou University in 1987. Currently, she is academician of CAS and TWAS, members of IUTAM's Congress Committee, vice-chairman of the China Association for Science and Technology, director of the Center for particle-laden turbulence, Lanzhou University, Editor-in-chief of Acta Mechanica Sinica, Associate Editor of Flow (2020~) etc. Her research interests include high-Reynolds-number particle-laden wall turbulence, multi-scale modeling and simulations of wind-blown sand movements. She is the founder of the Qingtu Lake Observation Array (QLOA) which is a unique field facility for scientific research on gas-solid two-phase flows in atmospheric surface layer with Re ~106 ~ 107.
Abstract: Sand storms and land desertification caused by surface wind shear and sand movement are perplexing environmental problems for human society, essentially the consequences of gas-solid two-phase wall turbulence with high Reynolds number. Taking the sedimentation of sand particles in particle-laden flows (such as wind-blown sand flow, sand storms, etc.) as the objective, this talk will firstly present experimental investigations on turbulence modulation caused by the interaction between particles and the wall in wind-blown sand flows. It is found that the presence of particle-wall (P-W) processes makes the VLSMs in particle-laden flows decrease significantly or even be broken down near the wall. Furthermore, field observations of sand storms, and a predictive model of the fluctuating wind velocity of a sand-laden wind field in the atmospheric surface layer are introduced. It is revealed that different-scale turbulent structures and their modulations are key factors affecting the prediction of sand-laden wind fields. Finally, a trans-scale simulation method aiming to reproduce the evolution process of a sand-dune field formed by sedimentary sand particles is proposed to realize quantitative simulations of the formation and evolution of a sand-dune field and to predict the expansion speed of a desert edge.
Enjoy free access to papers in support of Zheng's talk, courtesy of the Journal of Fluid Mechanics.
Modern applications of classical ideas in fluid mechanics: thin films, physical chemistry and molecular biology
Howard Stone is the Donald R. Dixon ’69 and Elizabeth W. Dixon Professor in Mechanical and Aerospace Engineering at Princeton University. He took his PhD with Gary Leal on the topic of drop deformation and breakup (1982/88) and was then a postdoc with John Hinch at Cambridge University; Gary had been a postdoc with George Batchelor and John was Batchelor’s PhD student. Howard was an Associate Editor of JFM 1997-2007, originally appointed by Batchelor. Howard works primarily on low-Reynolds-number flows and is still thrilled by the many variants of fluid mechanics problems and their applications in science and engineering.
Abstract: Fluid mechanics has a rich history. Many classical ideas are discussed in Batchelor's An Introduction to Fluid Dynamics, which was written about the time (mid-1960s) that he was transitioning from a research focus on turbulence to studies of microhydrodynamics. The latter motivates the themes for this talk, where we provide two examples from the subjects of thin film dynamics and cellular biology. First, we document experimentally the time and (three-dimensional) space variations of the shape of a falling film near the edge of a vertical plate, which we will understand using a novel similarity solution, where three independent variables and a partial differential equation can be collapsed to an ordinary differential equation.
Second, we discuss the formation of the spindle in a dividing cell, and report experiments documenting a condensed protein phase on growing microtubules. This configuration leads to discrete droplets along a microtubule, driven by the Rayleigh-Plateau instability, and the droplets are sites where branching nucleation is triggered. We argue that this "structure-function" connection is consistent with the kinetics of the multiple molecular species necessary to initiate nucleation of a new microtubule.
(The work involves many collaborators at Princeton including Bernardo Gouveia, Sabine Petry, Sagar Setru, Josh Shaevitz, and Nan Xue.)
George Batchelor - a personal reminiscence
Keith Moffatt FRS is Emeritus Professor of Mathematical Physics at the University of Cambridge, and Fellow of Trinity College, Cambridge. He took his PhD on Magnetohydrodynamic Turbulence 1958/62 under the supervision of George Batchelor and was joint Editor of JFM with him from 1966 to 1983. He has worked mainly in dynamo theory and magnetic relaxation, with occasional digressions into low-Reynolds number flow and free-surface flows. Known primarily for 'Moffatt eddies' in corner flows, and for the promotion of 'helicity' as a springboard for the sub-field of 'topological fluid dynamics', he is also keenly interested in the finite-time singularity problem.
Abstract: I shall describe my interactions with George Batchelor from the time I became his Research Student in 1958 until his death in March 2000, just a few weeks after his 80th birthday. I remember well how he encouraged me to participate in the famous Turbulence Colloquium held in Marseille in 1961; this was organised in a unique style by George in collaboration with L. Kovasznay and A.Favre; the Proceedings of that meeting stood as the foundation stone for turbulence research in subsequent decades. I recall also a memorable car journey in 1963 with George and Wilma and their three young daughters through Holland, Germany and Czeckoslovakia (as it then was) to Zakopane in Poland, where the biennial meeting on Fluid Mechanics was held that year. George roped me in as a copy-editor of JFM from 1961, and as joint Editor with him from 1966 to 1983 when I relinquished this responsibility. We were fortunate that George himself felt able to continue as Founding Editor until his death. I was very much involved with George in the early years of DAMTP and in the move to its Silver Street premises in 1964. Only when I succeeded him as Head of DAMTP in 1983 did I begin to appreciate the magnitude of his achievement in establishing a department of world renown in which fluid mechanics played such a central role. I shall comment also on George's key role in IUTAM, stemming from his brilliant revelation of the Kolmogorov theory at the Paris Congress in 1946.
Click here to access a pdf of Keith Moffatt's talk
Enjoy free access to papers in support of Moffatt's talk, courtesy of the Journal of Fluid Mechanics.