# Séminaire de Mécanique d'Orsay

## Le Jeudi 10 novembre à 14h00 - Salle de conférences du LIMSI

### From the dynamics of a hydraulic jump to the the asymmetric character of stellar explosions

## Thierry Foglizzo

Service d'Astrophysique, CEA Saclay

The SWASI fountain is a shallow water experiment involving a stationary hydraulic jump in a radial converging flow.
Initially circular, the hydraulic jump becomes oscillatory and turns into a self sustained rotating pattern.
Numerical simulations and perturbative analysis demonstrate that this unstable dynamics is due to the interactions of shear waves and surface gravity waves.

Using the analogy between hydraulic jumps in shallow water and shock waves in a compressible gas, this fountain reveals the dynamics of a collapsing stellar core before a supernova explosion. The astrophysical length scales are one million times longer and the timescales are one hundred times shorter than in this laboratory analogue.

Owing to a global rotation of the fountain, the most recent setup accounts for the angular momentum in the stellar core. A new spiral mode of instability, fed by differential rotation, has been characterized using surface PIV. The shallow water modeling of this 60cm experiment and its scaling to a larger size will be discussed.