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Christophe Gissinger
Associate professor at Ecole Normale Superieure (ENS Paris)
TURBULENCE

The study of turbulence is one of the most active research area. We developed several laboratory experiments in order to adress various questions related to turbulence, like the transport properties of turbulent flows, the dimensionality of turbulence or its statistical properties.

Turbulent transport: A long-standing question in fluid mechanics is to understand how angular momentum is transported by a turbulent flow. This question is also crucial for several celestial bodies. For instance, the exact mechanism by which the huge acccretion rates around black holes are generated is still unknown. Similarly, stellar interiors generally show rotation rates much slower than what is predicted by classical theories. I am therefore interested in the turbulent transport of angular momentum using both experimental and theoretical approaches.

lvks experiment
Tayler-Spruit dynamo

Energy cascade and coherent structures in turbulent flows: In many fluid systems, energy transfer across different scales is governed by the dimensionality of the flow and the nonlinear interactions between these scales. For example, when the flow is strongly constrained in one direction (such as in rotating flows, thin layers, or in the presence of a magnetic field) 2D turbulence can emerge, characterized by the transfer of energy towards larger scales. Conversely, a small number of capillary waves interacting nonlinearly can produce a direct 3D cascade of energy. Occasionally, organized and coherent structures, phase-correlated across the entire system, emerge within the chaotic turbulent flow, following mechanisms that are not well understood. Here are a few examples of the phenomena we are studying in this area.

zeroG
spectrum
Flicker
ENERGY

Energy conversion and the development of advanced energy technologies are crucial for addressing the growing global demand for efficient and sustainable energy solutions. Part of our research focuses on energy transformations in fluids, particularly regarding the mediation of energy conversions by fluid instabilities and the development of new technological applications. Here are a few examples, in the areas of liquid thermoelectricity, thermoacoustic cooling, and electromagnetic pumps.

thermoelec_setup
pem
thermoacou
CLIMATE, GEOPHYSICS and ASTROPHYSICAL FLUID DYNAMICS

Astrophysical fluid dynamics deals with the application of fluid dynamics to the motion of fluids encountered in space, such as planetary or stellar interiors, accretion disks and galaxies. Thanks to the growing amount of telescope observations and space missions in recent years, whole sections of the theory of such flows are now actively debated. In our group, we combine laboratory experiments, theory and numerical modeling to understand the mechanisms involved in some of these astrophysical systems.

Hydrodynamics of ocean worlds: it is now very clear that subsurface oceanic worlds are ubiquitous. For instance, it is believed that a vast ocean of salty water is present beneath the surface of several moons and planets of the solar system (Ganymede, Europa, Enceladus, Ceres, Titan, etc). Although this is perhaps the most common type of oceanic world, hydrodynamics of such subsurface oceans remains mostly unknown. I recently started a project aiming to develop a unified oceanography model for such subsurface oceans.

Europa-observations
Europa-simulations

Tornadoes and waves: Part of our activity focuses on the study of atmospheric and oceanic vortex motions, such as tornadoes and cyclones, and their complex interactions with turbulence, waves, and instabilities. We use laboratory experiments to study the stability of such flows and the associated wave dynamics, hoping to get a better understanding of these powerful phenomena and their impact on weather patterns and climate systems.

bathtub2

Magnetic field generation: Part of my activity is to explore new mechanisms for the generation of planetary magnetic fields, such as the possibility of centrifugal instability in planetary interiors or the existence of new induction processes related to inhomogeneities of the fluid properties.

dipole
vks
galaxy
CHAOS AND NON-LINEAR DYNAMICS

I also work on various non-linear problems, ranging from low-dimensional behavior in fluid dynamics to chaotic motions of mechanical systems. In general, one expects turbulent flows to show a very complex behavior, due to the infinite number of degrees of freedom. Yet, several turbulent systems, MHD or not, exhibit low-dimensional dynamics involving chaotic reversals between two symmetrical states. I work on deterministic or stochastic models aiming to understand such complex behaviors, using only a few modes in interaction.

chaos
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