Dynamical Significance of Turbulent Wall Layer Streaks

Abstract

The role of low speed streaks in the dynamical processes leading to the generation of Reynolds stress is investigated using ensembles of computed particle paths obtained from a direct numerical simulation of turbulent channel flow. Simultaneous visualization of appropriate Eulerian fields and trajectories of fluid particles which are most indicative of Reynolds stress production are given. These graphically illustrate the occurrence of ejection events at a series of discrete locations along low speed streaks. A strong association between streamwise vortices and the ejecting fluid is found. In particular, visualization of the ejecting fluid shows the presence of vortices which drive fluid from the sides up and over the low speed regions. As part of this process fluid from within the streaks appears to be entrained outward from the wall. Some of the implications of these results for turbulence modeling will be described.