Laboratoire
d'Hydrodynamique

Observations in nature as well as in laboratory flows reveal that turbulence in stably stratified media exhibits very peculiar features. The turbulent flows that prevail in such situations are organised in thin horizontal and decoupled layers in which vortices have a typical pancake shape. Until now, no theory has been able to satisfactorily explain the physical mechanism responsible for these layered structures and to predict their characteristic thickness. In order to do so, the dynamics of a prototype flow has been investigated in our laboratory and simulated numerically. lire la suite

Self-excited vortex formation in hot jets

Hot subsonic jets, when their temperature exceeds a critical value, are known to break up into a street of highly regular vortex rings. This phenomenon is observed in numerical simulations, and can be explained and predicted theoretically from global instability concepts. lire la suite

The regular vortex structures that form in hot jets emit sound into the far field. An analysis based on Lilley’s decomposition of aerodynamic source terms reveals that enthalpy fluctuations in the jet are responsible for the numerically observed dipole sound that emanates from the region of vortex roll-up. lire la suite