Self-sustaining processes at all scales in wall-bounded turbulent shear flows.
We collect and discuss the results of our recent studies which show evidence of the existence of a whole family of self-sustaining motions in wall-bounded turbulent shear flows with scales ranging from those of buffer-layer streaks to those of large-scale and very-large-scale motions in the outer layer. The statistical and dynamical features of this family of self-sustaining motions, which are associated with streaks and quasi-streamwise vortices, are consistent with those of Townsend's attached eddies. Motions at each relevant scale are able to sustain themselves in the absence of forcing from larger- or smaller-scale motions by extracting energy from the mean flow via a coherent lift-up effect. The coherent self-sustaining process is embedded in a set of invariant solutions of the filtered Navier-Stokes equations which take into full account the Reynolds stresses associated with the residual smaller-scale motions.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.
Institut de Mécanique des Fluides de Toulouse (IMFT) - Université de Toulouse, CNRS-INPT-UPS, 31400 Toulouse, France carlo.cossu@imft.fr y.hwang@imperial.ac.uk.|Département de Mécanique, École Polytechnique, 91128 Palaiseau, France.
Carlo
http://orcid.org/0000-0003-0876-6302
C
Cossu
Department of Aeronautics, Imperial College London, London SW7 2AZ, UK carlo.cossu@imft.fr y.hwang@imperial.ac.uk.
Yongyun
Y
Hwang
attached eddies; coherent lift-up; self-sustaining processes; wall turbulence