28 janvier 2020

Séminaire Carlo Cossu

Carlo Cossu has studied at the Università La Sapienza (Roma) for his PhD. He joined from 1999 til 2009 as Chargé de recherche the LadHyX, at the École polytechnique. He then worked as Professor and became in 2009 Directeur de Recherche CNRS at the Institut de Mécanique des Fluides de Toulouse (IMFT).
On the self-sustained nature of Townsend's attached eddies in wall-bounded turbulent flows

More than fifty years ago Townsend proposed that the dynamics of wall-bounded turbulent flows is associated, at least statistically, to a family of coherent motions which are self-similar in the logarithmic layer. Since then, a long quest for the identification of these structures and of their dynamics has captivated generations of fluid dynamicists. For a long time the most widespread wisdom has been that Townsend’s attached eddies consist of Λ-vortices, with kinetic energy produced by the smallest ones, living in the buffer layer, and then transferred to the, larger, logarithmic-layer ones and finally to the largest ones associated to large-scale (LSM) and very-large scale motions (VLSM).
In the talk I will summarize the results of ten years of investigations proposing an alternative view of the nature of Townsend’s attached eddies. Evidence will be shown of the existence of a whole family of self-sustaining motions with scales ranging from those of buffer-layer streaks to those of large-scale and very-large-scale motions in the outer layer. It will be discussed how these motions, associated with streaks and quasi-streamwise vortices, are able to sustain themselves at each relevant scale in the absence of forcing from larger- or smaller-scale motions by extracting energy from the mean flow via a coherent lift-up effect.


28 janvier 2020, 14h0015h00
LMFL Bâtiment M6 Avenue Paul Langevin, Villeneuve D'Ascq