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Instabilities, Waves and Turbulence

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Natural and industrial flows, in geophysics, aeronautics or process engineering, are complex, unsteady, sometimes multiphase, and most often turbulent. Understanding and modeling these flows is a real challenge for both fundamental and practical reasons.

On a global scale, atmospheric and oceanic flows are subject to stratification and background rotation effects. These lead to the generation of internal waves, which have a profound influence on the flow dynamics, such as the emergence of eddies or coherent jets that can influence the mixing properties (heat, pollutants ...)

On a smaller scale, flows with interfaces (either between two liquids or between a liquid and a gas) provide other examples of such complex flows. The formation of ocean waves illustrates the wide range of open issues, from the origin of the first ripples generated by wind to their amplification to the mechanism of saturation and dissipation by wave breaking. Other examples are the coiling instability of "liquid ropes" that fall on a surface and the surprising morphology of the "liquid curtains" that form at the exit of a horizontal pipe.

In this research group, we develop model experiments in simple and controlled configurations that aim to reproduce these complex flows from the first stages of instability to fully turbulent situations.

Permanent members:

P. Carles, P.-P. Cortet, A. Davaille, G. Gauthier, F. Giorgiutti, P. Gondret, J.-P. Hulin, J. Martin, F. Moisy, L. Pauchard, M. Rabaud, N. Rakotomalala, N. Ribe, D. Salin, L. Talon

Non Permanent members:

M. Brunet (PhD), M. Leang (PhD), S. Perrard (PostDoc)

Former Members:

S. Atis (PhD, 2013), F. Boulogne (PhD, 2013), A. Campagne (PhD, 2015), B. Gallet (PostDoc, 2013), E. Herbert (PostDoc, 2013), T. Lemee (PhD, 2013), N. Machicoane (PostDoc, 2016), A. Paquier (PhD, 2016), C. Ruyer-Quil (TA UPMC, 2013), B. Saintyves (PostDoc, 2013), A. Sibrant (PostDoc, 2017), R. Villey (PostDoc, 2016)

Inertial waves in a rotating fluid

N. Machicoane,P.-P. Cortet, F. Moisy

Collaboration : B. Voisin (LEGI, Grenoble).

Inertial waves are emitted from a sinusoidal disturbance in a homogeneous rotating fluid. The propagation of this wave is dispersive and anisotropic. Visualization of this phenomenon is achieved using a corotating Particle Image Velocimetry (PIV) system.

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N. Machicoane, P.-P. Cortet, B. Voisin, and F. Moisy, Phys. Fluids 27, 066602 (2015).

Kelvin wake or Mach cone?

M. Rabaud, F. Moisy

The angle of the wake behind a duck or a ship is always 39 degrees, independent of its velocity: this is the classical Kelvin wake. But is this really the case? A detailed analysis of a set of airborne images of ship wakes from Google Earth shows that the wake angle rather follows a law analogous to the Mach cone for supersonic airplanes. Why?

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F. Moisy, M. Rabaud Phys. Rev. E 89, 063004 (2014).

Rotating turbulence

N. Machicoane, A. Campagne, P.-P. Cortet, F. Moisy

Collaboration : B. Gallet (CEA Saclay).

The two-dimensional structuration of a turbulent flow in a rotating frame is a key mechanism for geophysical flows (ocean, atmosphere, rotating stars etc.) Using the rotating platform Gyroflow, we measure the anisotropic energy flux responsible for this two-dimensional structuration.

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Campagne A., Machicoane M., Gallet B., Cortet P.-P. and Moisy F., J. Fluid Mech 794, R5 (2016).

Machicoane M., Moisy F., and Cortet P.-P., Phys. Rev. Fluid 1, 073701 (2016).

Liquid rope coiling

N. Ribe
Collaborations: M. Habibi and D. Bonn

If you like honey on your toast at breakfast, you are ready to perform a simple and beautiful fluid mechanics experiment. Plunge a spoon into the honey jar, and then hold it vertically several inches above the toast. The falling honey builds a whirling corkscrew-shaped structure - a phenomenon called "liquid rope coiling".

(Photo H. Hosseini)

N. Ribe, J. Fluid Mech. 812, R2 (2017).

Torricelli's curtain: Morphology of laminar jets under gravity

M. Rabaud, N. Ribe

While the form of a fluid jet issuing horizontally from an orifice was first studied by Torricelli (1643), this classic problem in fluid mechanics still holds surprises. When a laminar jet issues from the end of a pipe, it divides into primary and secondary jets with a thin vertical curtain of fluid connecting them. We are currently using laboratory experiments and numerical simulations to study this unexpected behavior.

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Wind waves generation

A. Paquier, F. Moisy, M. Rabaud

How does wind create waves? This seemingly simple question has been the starting point of numerous theoretical, numerical, and experimental works of research. We approach this problem with a new experiment allowing to detect the very first deformations at the surface of a viscous fluid with an accuracy of a few microns.

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A. Paquier, F. Moisy, M. Rabaud Phys. Rev. Fluid 1, 234501 (2016).

Swirling a glass of wine

F. Moisy, J. Bouvard

Collaboration: W. Herreman (LIMSI, Universite Paris-Sud)

It is common knowledge that prescribing an orbital motion to a glass of wine generates a rotating gravity wave that comes along with a swirling mean flow. This mean flow rotates in the direction of the wave and recirculates poloidaly (radially and vertically), thus permanently pushing new fluid to the surface where it aerates and releases the wine's aromas. Precisely the same kind of orbital shaking is used on a more professional level in bioreactors for the cultivation of biological cells. We present here new experiments to capture the physical mechanism of mean flow generation in an orbital shaken fluid.

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J. Bouvard, W. Herreman, F. Moisy, Phys. Rev. Fluids 2, 084801 (2017)

Gravity induced mixing of two miscible fluids in vertical and tilted tubes

J. Znaien, F. Moisy, J.-P. Hulin
Collaborations: Y. Tanino, E.J. Hinch (DAMTP-Cambridge)

The buoyant mixing of two fluids of different densities in a tilted tube is investigated. The fluids are initially in an unstable configuration (the heavier fluid is above the lighter fluid), and show a rich variety of phenomena, including stable counterflows, intermittency and fully turbulent mixing.

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Y. Tanino, F. Moisy, J.-P. Hulin, J. Turbulence 16 (5), 484-502 (2015).

Lift Crisis

M. Rabaud

Collaboration: P. Bot, G. Thomas, A. Lombardi, C. Lebret (Naval Academy Research Institute, IRENAV Brest)

After the pioneering work of G. Eiffel (1912) the « Drag crisis » is now a well known phenomena of fluid mechanics for a bluff body moving at large velocity. During this crisis the drag force becomes, surprisingly, a decreasing function of the relative velocity. We have shown that at the drag crisis, non-up/down symmetrical bodies can also experience a strong "lift crisis", i.e. a sharp transition or even an inversion in their lift force.

Bot P., Rabaud M., Thomas G., Lombardi A. and and Lebret C., Phys. Rev. Lett 117, 234501 (2016) [PDF]