# Séminaire de Mécanique d'Orsay

## Le Jeudi 7 février à 14h00 - Salle de conférences du LIMSI

### Écoulements entraînés par des ultrasons

## Valéry Botton

LMFA, INSA Lyon

The fact that a sound wave propagating in a viscous fluid can be at the origin of steady motions is known since Faraday and Rayleigh; it is refferred to as "acoustic streaming". Our team in Lyon (France) is revisiting this phenomenon in the aim of developping engineering oriented models of acoustic streaming. This kind of flows is indeed present in applications such as sonochemistry and the use of ultrasounds for medical imaging and care. New fields of application can also be investigated such as the use of ultrasounds in crystal growth : this kind of flow can indeed improve heat and mass transfer in a non intrusive way; it can also be used to control natural convection instabilities. Similarly to other coupled problems (rotating flows, low magnetic Reynolds number MHD flows) the flows we study here can be considered as resulting for a weak coupling of an external field and the fluid motion. The external field is of course the acoustic field, ruled by propagation laws and the fluid dynamics can be described by the uncompressible Navier-Stokes equation featuring an "acoustic streaming force" term. The presentation will give an overview of our approach and results combining experimental, theoretical and numerical works.