Mechanism of Self-Sustenance and Regeneration of Quasi-Streamwise Vortices of Near-Wall Turbulence

Abstract

Quasi-streamwise vortices observed in near-wall turbulence arranged in a typical zigzag pattern in the streamwise direction are investigated by analyzing the flow field of data bases obtained by both high-resolution LES and numerical integration of the parabolized Navier-Stokes equation for channel flow, focusing attention on the mechanism of self-sustenance and regeneration. It has been revealed that quasi-streamwise vortices are inherently self-sustaining. Namely, they achieve their streamwise vorticity by stretching the spanwise vortices of mean flow by means of self induced velocity fields. The analysis of the regeneration mechanism also shows that the quasi-streamwise vortices have inherent potential to regenerate themselves using their own velocity fields. The approximate quasi-three-dimensional simulation based on the parabolized Navier-Stokes equation confirms the conclusions of the analysis of the LES data base.