Laboratoire de Mécanique des Fluides et d'Acoustique - UMR 5509

LMFA - UMR 5509
Laboratoire de Mécanique des Fluides et d’Acoustique
Lyon
France


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Accueil > Activités de Recherche > Turbulence et Instabilités > Séminaires informels > Séminaires passés

Claude Cambon

De l’hélicité partout ou nulle part ? Bilan et perspectives en turbulence avec rotation, stratification, cisaillement (NSf !) et couplages magnétohydrodynamiques.

Mardi 30 mai, 13h, ECL Bât I11 salle de réunion 1er étage

De l'hélicité partout ou nulle part ? Bilan et perspectives en turbulence avec rotation, stratification, cisaillement (NSf !) et couplages magnétohydrodynamiques.

Although rotating flows are often considered to be helical, this is not necessarily the case for homogeneous turbulence with supporting arguments based on a rigorous statistical analysis. Of course, local turbulent patches, snapshots, or special flow realizations containing helicity are sometimes observed in several Direct Numerical Simulation (DNS) studies of homogeneous rotating turbulence. Nonetheless, the rise of statistically significant helicity spectrum is never found in the absence of ad hoc initialization or forcing. Even when considering weak turbulence propagating from a local blob, or cloud, of vorticity, coexisting pairs of inertial waves with opposite polarities yield exactly zero helicity. On the other hand, net helicity is created near a wall in rotating turbulence, and then could be transported towards the core of the flow, as confirmed in the DNS database : it is found that the sign of helicity is correlated with the motion of an eddy with axis normal to the wall and axial motion. Helicity of two such eddies, with up and down opposite axial motion is additive.