Research
UNDER (very slow) PROGRESS...
Instabilities and Turbulence in Rotating Fluids
Rayleigh-Bénard convection: coupling with rotation and stable-stratification
Coupling between rotation, stable stratification and thermal convection is ubiquitous in atmospheres, liquid planetary cores and stellar interiors. I am particularly interested in the inverse cascade observed in very rapidly-rotating convection. More recently, we also started several projects involving the interaction between a stably-stratified layer and a turbulent convective layer, mimicking the interaction between the troposphere and the stratosphere in our atmosphere or between radiative and convective zones inside stars.
Collaborators: Michael Le Bars, Louis-Alexandre Couston, Daniel Lecoanet
Melting/Freezing interfaces
We consider the dynamical interaction between a fluid phase with intense motions and a solid phase of a pure component. The Stefan boundary conditions are modelled using a phase-field approach and the Navier-Stokes equations are penalized in the solid. This flexible approach allows us to consider various problems from standard Rayleigh-Benard convection to the melting of objects in imposed flows or coupled with natural convection. These simple models can be used to study the fundamental processes at play in the melting of ice shelves, convection in magma chambers or even the formation of solid cores in terrestrial planets.
Collaborators: Laurent Duchemin, Jhaswantsing Purseed
Magnetohydrodynamics
Flexible fibres in Turbulence
How is a flexible fibre deformed when advected by a turbulent flow? The motion of a flexible fiber in a turbulent flow is studied both experimentally and numerically. We developed a simple numerical model solving the 1D elastica driven by the viscous drag forces from an idealized turbulent flow. The curvature statistics are studied showing unusual behavior when the fiber length lies in the inertial range.
Collaborators: Gautier Verhille, Amélie Gay
Thanks to Joseph Lazzari for the discovery of the beach!
Large-scale vortex mode in rapidly-rotating RB convection with L. Silvers and M.R.E. Proctor (DAMTP)
Forced inertial waves in spherical shells with C. Baruteau and G. Ogilvie (DAMTP), and A. Barker (Northwestern University).
Currently using the PARODY code (E. Dormy and J. Aubert) to study the nonlinear behaviour of tidally forced inertial modes in spherical shells.
Dynamo theory with M.R.E. Proctor (DAMTP).
Effect of magnetic boundary conditions on kinematic dynamo action.
Transition from small-scale to large-scale dynamos and pumping effect in simple flows.
Magnetic buoyancy instability with M.R.E. Proctor and W. Edmunds (DAMTP), L. Jouve (IRAP Toulouse) and L.J. Silvers (City London).
See our recent paper.
Unstably stratified turbulence (with A. Delache and F.S. Godeferd, LMFA).
I'm studying homogeneous turbulence submitted to a uniform gradient of density in the Boussinesq approximation.
This system can be considered as a steady Rayleigh-Taylor instability and is an interesting and more realistic way (compared to stochastic forcing) to make the turbulence quasi-steady.
The effect of rotation and eventually the addition of the induction equation are also under consideration.
On the right, you can see the fluctuating density in a 512^3 simulation.
Rotating compressible convection (with P.J. Bushby, Newcastle University).
At Newcastle University, I was working on the dynamo properties of a convective layer of compressible fluid rotating about the vertical. This type of flows is sufficiently simple to be numerically tractable, but contains many of the important dynamics existing in realistic astrophysical or geophysical flows (namely the convective zone of the Sun or the liquid Earth's core).
In the Boussinesq approximation, these flows and their ability to sustain a magnetic field are well-known.
A striking result is their inability to generate a mean magnetic field despite the strongly helical nature of the flow (see Cattaneo & Hughes, J. Fluid. Mech. 553, 2006), which is in contradiction with the classical mean-field theory (see for example Moffatt, CUP, 1978).
I'm trying to generalize these results to the compressible case, in which the symmetry about the mid-layer is broken.
On the right, I show an example of the temperature (red for cold, yellow for hot fluid) in such convective flows, and some streamlines around a helical down flow (colours correspond to the local value of the enstrophy).
Homogeneous anisotropic turbulence (with C. Cambon, F.S. Godeferd and A. Delache, LMFA).
During my PhD, I was working on Homogeneous Anisotropic Turbulence.
This type of flows includes rotating turbulence, magnetohydrodynamic turbulence submitted to an imposed magnetic field, stratified turbulence...
I focused on the effect of rotation and magnetohydrodynamics, and the coupling of these two effects.
Currently, I'm working on the comparison between Direct Numerical Simulations and spectral closures such as EDQNM.
The unstably stratified homogeneous turbulence, and its link with the Rayleigh-Taylor instability, is also under consideration.
On the right, a volume rendering of enstrophy of homogeneous isotropic turbulence form DNS is shown., and some streamlines around a vortex.
Penalization methods in spectral codes
Recently, and in collaboration with Fabien S. Godeferd and Clément Jause-Labert, I have considered confined turbulence and penalization methods in spectral codes.
This immersed boundary method allows to impose no-slip or stress-free boundary conditions (and is also applicable to confine magnetic fields) on an arbitrary geometry.