
Jacques Magnaudet
Présentation
I am a senior researcher at CNRS (the French National Center for Scientific Research), working at the Fluid Mechanics Institute of Toulouse (IMFT).
My research focuses on several fundamental aspects of hydrodynamics and turbulence in two-phase flows and inhomogeneous fluids, mostly studied by means of computational and theoretical approaches. I also closely collaborate with experimentalists and occasionally directly supervise simple experiments myself.
I am especially involved in two main areas:
• the dynamics of particles, drops and bubbles, most notably:
- the determination of forces acting on these objects when they move in non-uniform or time-dependent flows;
- their hydrodynamic interactions with similar neighboring entities or walls;
- the motion and possible trapping of particles and bubbles in vortical structures and the way they may collectively alter/destroy vortices or generate specific flow patterns;
- how phase change (evaporation, boiling, condensation) or contamination by surfactants modifies the dynamics of rising bubbles and spreading drops;
- the topological changes that may be experienced by large rising bubbles or drops spreading on a liquid surface in the presence of Marangoni effect;
- the path instability and subsequent style of paths of bubbles and rigid bodies freely moving under the effect of an external force (such as gravity/ buoyancy);
- the dynamics of particles and bubbles crossing a sharp interface separating immiscible liquids;
- the specific flow structure and dynamics of rigid particles settling or rising in density-stratified and rapidly-rotating fluids.
• the structure, mixing properties and near-surface interactions of non-standard inhomogeneous turbulence, especially:
- inter-component transfers and boundary layer structure in free-surface turbulence;
- high-Schmidt-number mass transfer across walls and free surfaces;
- the peculiar structure of turbulence and mean currents beneath surface waves;
- the generation of surface waves on viscous liquids by a turbulent air flow;
- the physics of gravitationally-induced turbulence in open and confined geometries;
- the dynamics of confined high-Reynolds-number gravity currents.
Other topics I am or have been involved in include:
- complex two-phase flows (liquid-liquid phase inversion, sudden emptying of liquid-filled containers);
- fluid slip at rigid surfaces (influence on the dynamics of bluff-body wakes, generalization of the Navier condition to rough surfaces, drag reduction by air-filled micro-cavities);
- dynamics of droplet chains and living cells in microchannels;
- numerical techniques for two-phase flows (interface capture, modeling of viscous stresses).
To study these problems and phenomena, I use and sometimes develop a variety of techniques and methodologies. Some of them are analytical, including perturbation approaches, reciprocal theorems and vector field decomposition. Most others are computational. In particular, I developed, first by myself, then with successive generations of students and colleagues, the in-house code JADIM that solves the Navier-Stokes equations, possibly coupled with the transport of passive or active scalars such as temperature, density or surfactant concentration. This code includes boundary-fitted and fixed-grid approaches thanks to which interfacial phenomena may be accurately captured. It allows fully-resolved simulations of two- and three-phase incompressible flows, possibly with moving rigid bodies and interfacial topological changes, from viscous-dominated to fully turbulent regimes.
Together with my students and colleagues, I employ these various and complementary tools to dissect and model the physical mechanisms at play in the above types of flow. This frequently yields predictions in the form of generic laws that are then used to understand, predict and sometimes optimize the properties of complex flows of engineering or geophysical relevance.
More specifically, through various collaborations with industrial and institutional partners, I have been directly involved in a variety of problems related to nuclear safety (cooling circuits, accident scenarios), steelmaking, chemical engineering (gas separation, fluidization, microfluidics), oil recovery (mixing in wellbores), transportation (interfacial phenomena in aircraft and launcher tanks, bubble-induced drag reduction), defense (bubbly wakes, container emptying, inertial confinement), air-sea interactions (wind-induced waves and near-surface turbulence, CO2 transfer and sequestration), marine pollution (microplastics, oil spills) and volcanology (viscous mixing in magmatic chimneys).
A list of my publications in peer-reviewed journals may be found at:
• https://www.webofscience.com/wos/woscc/citation-report/a6fad07b-4a92-4ac7-be52-bcb877d04314-fc04f321
• https://scholar.google.fr/citations?user=bVYTlS4AAAAJ&hl=fr&oi=ao
Records of some talks I gave over the last few years are available through the links below:
• Falling styles of gravity/buoyancy-driven disks, ICTS Distinguished lecture (Bengaluru, 2019):
https://www.youtube.com/watch?v=UUZzh740_Ls
• Interplay of a pair of rising bubbles released in line, Multiphase Flows - Advances and Future Directions (online, 2021):
https://www.youtube.com/watch?v=A4J6AqcESy0
• Particles and bubbles getting through interfaces and stratified layers, IJMF Spotlight seminar (online, 2023):
https://www.youtube.com/watch?v=wlsu8H9lbgQ
• Maxworthy's 1970 experiment on a computer, Perspectives in Hydrodynamics (IIT Bombay, 2024):
https://www.youtube.com/watch?v=i2kPQqBZVMA
• From Leonardo to Stabfem: The long story of path instability of rising bubbles made short, Sectional lecture, 26th ICTAM (Daegu, 2024):
https://app.videas.fr/6b0ce61c-3f1b-4648-93ca-a38860f74061/
Short videos illustrating some of the physical problems I investigated are also available here:
• Buoyancy-driven turbulent mixing of two immiscible fluids in an inclined pipe (paper here https://hal.science/hal-01102240/document)
Two fluids with slightly different densities and identical viscosities are unstably superimposed in a long circular pipe inclined by 15 degrees to the vertical. The fluids are slightly viscous, so that the flow that sets in quickly becomes turbulent. The first of these DNS-based videos provides an overview of the flow dynamics throughout the pipe; colors correspond to isopycnal surfaces, from C=0.9 (blue) to C=0.1 (red), with C=1 referring to the heavy fluid. The second video provides a closer view at the dynamics of the ascending fluid by visualizing the evolution of the C=0.1 iso-surface. The latter is colored by the "swirling strength" intensity, a criterion that helps identify three-dimensional vortical structures:
https://app.videas.fr/1ff8f78d-3acf-491b-8dac-bec6e094303b/
https://app.videas.fr/9444fdfc-379b-4625-b776-230d54858b4c/
• Falling styles of gravity-driven disks (paper here https://hal.science/hal-00908124/file/auguste_10246.pdf)
An infinitely thin rigid disk is released from rest broadside on in a slightly viscous fluid. The type of path followed by the disk depends on the ratio of inertial and viscous forces it experiences and on the disk-to-fluid inertia ratio. The first of these DNS-based videos displays the fall of a thin disk performing large-amplitude planar zigzags. In the second video, the disk has more inertia with respect to the fluid and performs complete tumbles; colors reveal the wake structure, based on the lambda2 criterion:
https://app.videas.fr/6c38932f-296b-4117-bea5-fc73005e59a5/
https://app.videas.fr/ed05d78e-6954-46e1-bd47-c65ba0df5c30/
• Les gouttes qui pulsent, a short outreach video (in French) produced by CNRS https://images.cnrs.fr/video/6499, based on this paper:
https://www.nature.com/articles/s41467-018-03201-3
A more complete video showing the full experimental sequence analyzed in the paper is available at https://app.videas.fr/893529ac-a0a2-40dd-bc6d-52660c4d8cb5/
A millimeter-sized dichloromethane drop is released on an aqueous bath in the presence of a surfactant, CTAB. The drop spreads over the bath surface. Evaporation-driven Marangoni stresses develop and induce a rim at the edge of the dichloromethane film. The Rayleigh-Plateau instability produces successive circular droplet crowns, while an evaporative instability induces radial wrinkles in late stages. Time variations of interfacial tensions resulting from droplet ejections and specific properties of CTAB make the system able to perform successive large-amplitude pulsations.
• Fragmentation of the tail past a steel marble crossing an interface separating two immiscible liquids
(paper here https://hal.science/hal-01660835/file/pierson_19284.pdf)
Steel marbles settle in a silicone oil layer before they cross the interface separating this layer from a water bath. Because of their large density, they easily cross the interface and settle within the water bath with a significant speed, towing a long column (tail) of silicone oil. Provided the oil viscosity is not too large, the Kelvin-Helmholtz instability that develops soon at the tail surface yields a massive fragmentation phenomenon by which the tail breaks up into a myriad of droplets. The silicone oil if 50 times more viscous than water in the first experimental sequence, and is only 5 times more viscous in the second one:
https://app.videas.fr/57b39efd-0a2f-4581-bf8f-7a7aa9728263/
https://app.videas.fr/cec4763e-1b05-43bd-8a70-b2ac9192eacb/
• Air bubbles crossing an interface separating two immiscible viscous liquids
(paper here https://hal.science/hal-00908876/file/Bonhomme_10245.pdf)
These three videos illustrate the complex influence of the viscosity jump encountered by a bubble crossing an interface separating two liquids, and that of the bubble size which dictates its equilibrium shape in the lower fluid. In the first video, an air bubble with a diameter d≈7mm rises first through a very viscous water-glycerin mixture, then through a silicone oil 50 times less viscous. The bubble is slightly larger (d≈11mm) and the two fluids have nearly equal viscosities in the second video. The third video shows a d≈20mm bubble rising first in water, then through a silicone oil 10 times more viscous. As the three videos make clear, increasing the bubble size yields strikingly different shapes (spheroidal, then spherical cap and finally toroidal), while varying the viscosity ratio has a deep impact on the breakthrough dynamics as well as on the geometry and volume of the tail of lower fluid entrained by the bubble.
https://app.videas.fr/e0a6cc53-6082-4cd0-9ade-e7a6dded4502/
https://app.videas.fr/d721e1c7-5753-4534-9f7d-5dc248ec2a6b/
https://app.videas.fr/46490fae-8c9b-48a9-a247-16f07434ea8a/
Domaines de recherche
Publications
Publications
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Experimental characterization of the gas phase during bottle emptying10th International Conference on Multiphase Flow, May 2019, Rio de Janeiro, Brazil
Communication dans un congrès
hal-04728850
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Simulating the emptying of a water bottle with a multi-scale two-fluid approach2nd International Workshop of Non-Invasive Experimental Tools and Numerical Methods for the Investigation of Non-Reactive and Reactive Gas-Liquid Flows, Jun 2018, Hambourg (Germany), Germany
Communication dans un congrès
hal-04728788
v1
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Simulating the emptying of a water bottle with a multi-scale two-fluid approach1st NEPTUNE_CFD user meeting, Apr 2018, Saclay (92), France
Communication dans un congrès
hal-04727883
v1
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Simulating the emptying of a water bottle with a multi-scale two-fluid approach5th Joint US-European Fluids Engineering Division Summer Meeting, ASME, Jul 2018, Montreal (Canada), Canada. ⟨10.1115/FEDSM2018-83196⟩
Communication dans un congrès
hal-04728811
v1
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Assessment of multi-scale two-fluid approach by simulating the emptying of a bottleDispersed Two-Phase Flows, SHF, Sep 2018, Toulouse, France
Communication dans un congrès
hal-04728828
v1
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Path instabilities of heavy bodies in free fall in a viscous fluid: wake dynamics vs. aerodynamic effects66th APS DFD Annual Meeting, Nov 2013, Pittsburg, Etats-Unis, United States
Communication dans un congrès
hal-04481514
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Weakly nonlinear analysis of the flutter motion of thin cylindersErcoftac International Symposium on Unsteady separation in Fluid-Structure Interaction, Jun 2013, Mykonos, Greece
Communication dans un congrès
hal-00918002
v1
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The hard life of air bubbles crossing a fluid/fluid interfaceComplex Fluids & Flows in industry & nature II, Jul 2013, Vancouver (Canada), Canada
Communication dans un congrès
hal-04481446
v1
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The rich life of light rising spheres66th APS DFD Annual Meeting, Nov 2013, Pittsburg, Etats-Unis, United States
Communication dans un congrès
hal-04481492
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Linear stability of disks falling or rising freely in a viscous fluid9th Euromech Fluid Mechanics Conference, Sep 2012, Rome, Italy
Communication dans un congrès
hal-00918006
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Ecoulement d'un fluide visqueux autour d'un disque en incidence frontaleCFM 2007 - 18ème Congrès Français de Mécanique, Aug 2007, Grenoble, France
Communication dans un congrès
hal-03362031
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Forces et couple sur une bulle ellipsoïdale plongée dans un écoulement cisailléCFM 2007 - 18ème Congrès Français de Mécanique, Aug 2007, Grenoble, France
Communication dans un congrès
hal-03362123
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Large eddy simulations of Rayleigh-Taylor turbulence5th International Symposium on Turbulence, Heat and Mass Transfer, Sep 2006, Dubrovnik, Croatia. pp.117
Communication dans un congrès
hal-00189734
v1
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