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Conf’luence S. Le Dizès

21 mars 2011

Radiative instability of stratified shear flows
vendredi 1er avril 2011 à 14h
Amphithéâtre Nougaro
Stéphane Le Dizès, IRPHE, CNRS & Aix-Marseille Université

Résumé :
In this talk, I analyse how the stability of a shear flow is modified when placed in a stably stratified fluid. I first show that stratification is stabilizing only if the directions of shear and stratification are aligned. When shear and stratification are not aligned, I demonstrate that an additional inviscid instability associated with the emission of internal gravity waves can take place. This radiative instability is analysed in details for models of boundary layer flows, plane jets and rotating flows. Both the mechanism of instability and explicit formulas for the characteristics of the instability are provided. Experimental results are also obtained for two types of rotating flows (a Gaussian vortex and the flow around a rotating cylinder when the rotation axis is aligned along with the direction of stratification). Finally, the results are discussed in the context of atmospheric flows and of astrophysical flows (accretion disks).