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Accueil > Pages personnelles > MAGNAUDET Jacques

MAGNAUDET Jacques

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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 or occasionally directly supervise simple experiments.

I have been especially involved in two main areas :

the dynamics of bubbles, drops and particles, most notably
- the determination of forces acting on these entities when they move in non-uniform or time-dependent flows ;
- their hydrodynamic interactions with similar neighboring entities or with walls ;
- the motion and possible trapping of bubbles in vortical structures and the way a collection of bubbles alters vortices or generates specific flow patterns ;
- how phase change 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 of bubbles and rigid bodies freely moving under the effect of gravity or buoyancy ;
- the dynamics of bubbles and particles crossing a sharp interface separating immiscible liquids ;
- the flow structure about rigid particles settling in a density-stratified fluid and their specific dynamics.

the structure, energy transfers across scales, and mixing properties of non-standard inhomogeneous turbulence, especially
- spectral transfers and boundary-layer structure in free-surface turbulence ;
- high-Schmidt-number mass transfer across walls and free surfaces ;
- the structure of turbulence beneath surface waves ;
- the physics of gravitationally-induced turbulence in open and confined geometries ;
- the consequences of wall and end effects on the dynamics of gravity currents.

To study these phenomena, I have used and sometimes developed a variety of techniques. Some of them are analytical, including perturbation approaches or vector field decomposition, most are computational. In particular, I developed, first by myself, then with successive generations of students and colleagues, the in-house computational code JADIM that solves the Navier-Stokes equations, possibly coupled with the transport of an active scalar such as temperature, density or surfactant concentration. This code includes boundary-fitted as well as fixed-grid approaches, allowing an accurate capture of interfacial phenomena ; it is suitable for performing direct numerical simulations of two- and three-phase flows, possibly with rigid moving bodies and interfacial topological changes, from low-Reynolds-number to fully turbulent regimes.

Thanks to these various tools, I try with my students and colleagues to disentangle and dissect the physical mechanisms at play in the above types of flow. This frequently yields predictions in the form of generic laws that may then be used by the relevant community to understand, predict and sometimes optimize the properties of complex flows of engineering or geophysical relevance.

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Short Vitae
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Publications (11/2018)

Contact
Jacques Magnaudet
Institut de Mécanique des Fluides de Toulouse
Allée du Professeur Camille Soula, 31400 Toulouse, France
E-mail : jmagnaud@imft.fr
Phone +33 (0)5 34 32 28 07


Some videos illustrating several problems I have been recently interested in

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Bubble rising across an interface_1
A 7mm large spheroidal air bubble crossing a water-oil interface (the oil is approximately 60 times less viscous than water). From Bonhomme et al. (JFM 707, 2012).
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Bubble rising across an interface_2
Same as in the previous video with a 1.8cm large toroidal bubble (the oil is approximately 10 times more viscous than water).
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Liquid-liquid fragmentation_2
Same as in the previous video with an oil 50 times more viscous than water.
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Liquid-liquid fragmentation_1
The oil tail dragged by a steel sphere falling into water breaks up into a myriad of droplets (the oil is 5 times more viscous than water). From Pierson & JM (JFM 835, 2018).
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The amazing dynamics of a dichloromethane drop released on a water substrate
A dichloromethane drop is released on a water bath. A specific surfactant, CTAB, is present in both liquids. A marked rim quickly develops at the outer edge of the film that spreads around the drop, and eventually breaks up into a series of droplets, due to Rayleigh-Plateau instability. The film experiences regular pulsations, corresponding to a succession of spreading and dewetting stages. A specific structure made of radial wrinkles develops during the fourth pulsation. From Wodlei et al. (Nat. Commun. 9, 2018).
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Freely falling disk_1
A freely falling disk with weak inertia follows a fluttering path with large-amplitude zigzags. From Auguste et al. (JFM 719, 2013).
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Freely falling disk_2
Same as in the previous video for a disk with a 4 times larger inertia. The disk now tumbles while drifting sideways as it falls.
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Gravitational mixing in a tilted tube
Detail of the early stages of the evolution displayed in the previous video.
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Gravitational mixing in a tilted tube
Two fully miscible fluids with a small density difference are initially placed in an unstable configuration in a long circular pipe closed at both ends. Gravity-driven turbulent mixing sets in when the tube is tilted from vertical. Colors identify isopycnals, with blue (red) corresponding to pure heavy (light) fluid. From Hallez & JM (JFM 762, 2015).