Multiscale analysis of some shear layers in a fully developed turbulent channel flow

Abstract

Multiscale edge detection-wavelet analysis is applied to the velocity field emanating from direct numerical simulations of a fully developed turbulent channel flow. The direct numerical simulations are realized in large computational domains at four different Karman numbers up to 1100. The shear layers (SL) related to the streamwise and spanwise velocity fields involving streamwise and spanwise gradients are analyzed scale-by-scale, over the homogeneous planes. The SL involving the spanwise gradient, in particular the wall vorticity layers surrounding the quasi-streamwise vortices (QSV) are organized into long streamwise streaks, whose spanwise spacing and thickness are determined versus the wavelet-wavenumber. The shear layers related to the streamwise gradient are further analyzed by using the Rice decomposition of the wavelet coefficients into a local phase and a local amplitude. Large zones of constant phase with slowly varying local amplitude have been identified at different scales. It is found that the constant phase-locked regions coincide with the wakes of the buffer layer QSV. The arrival of the quasi-streamwise vortices cause phase jumps and large intermittency in the local amplitude. The analogy between these peculiarities and the imperfect chaos synchronization phenomena together with the consequences in term of wall turbulence control are discussed. These results confirm globally our previous investigation realized through a low Reynolds number channel flow DNS in a small computational box and clarify some points that could not then elucidated.