Research

I work on planetary fluid interiors, where rotation, orbital forcing and boundary geometry shape the motion of liquid cores. Tides, precession and libration excite flows and waves ; topography and stratification change how those flows exchange energy and angular momentum with the rest of the planet. I combine theory, numerical simulations and laboratory experiments to follow these connections.

Forcing, waves and magnetic fields

Could mechanically driven flows help explain an ancient lunar dynamo ? In Le Bars et al., (2011), we studied the tidal route, while our precession calculations (2019) tested how much flow and dissipation a lunar core could sustain. The possible source of an ancient field remains a quantitative question.

In a non-spherical core, waves and instabilities have a rich geometry of their own. With Jérémie Vidal, I have studied inertial, acoustic and hydromagnetic modes in ellipsoids. The ZoRo experiment also led us to explore acoustic velocimetry. Vidal’s numerical tools offer another way to study the modes and their stability.

Density stratification adds gravito-inertial waves and changes the conditions for dynamo action. In Pružina et al. (2025), we showed that semiconvection can sustain a magnetic field in a stratified layer. I am interested in how this physics combines with rotation, forcing and non-spherical boundaries.

Topography, drag and turbulence

Topography can transfer angular momentum between a fluid core and its solid boundary. Rémy Monville, Dominique Jault and I studied this coupling with a local model. In Giraud et al. (2026), we then examined inertial-wave drag over topography in rapidly rotating fluids. Mechanical forcing can also produce mean zonal flows, even when the imposed motion is weak.

The THEIA project (2020–2026) developed numerical approaches and a large rotating experiment for these questions. Its one-metre apparatus was commissioned and the first spin-up experiments, with flat and rough bottoms, were performed in 2026. We are analysing those runs and exploring how waves, stratification and turbulence alter topographic drag.

From core flows to planetary observations

Nutations, variations in the length of day and magnetic-field changes can constrain the dynamics of the deep interior. We ask which signatures could arise from waves, boundary torque or magnetic coupling. In Personnettaz et al. (2026), we investigated viscous and ohmic damping of inner-core translation, a useful example of how theory can sharpen an observational question.

Beyond planetary cores, my magnetohydrodynamics collaborations have included protostellar spin-down, massive binary stars and a teaching experiment with an MHD boat.