Effects of mean flow skew on turbulent shear layers. Part I. Numerical investigation

Abstract

Skewed turbulent shear layers, formed by the interaction between two non-aligned turbulent boundary layers, are investigated using high-fidelity large eddy simulations in a temporally evolving framework. It is argued that a skewed shear layer of this form should be viewed, in the long-time limit, in a rotated reference frame as the superposition of a standard planar shear layer and an orthogonal jet-like component that decays in time. The skewed shear layer is found to have reduced vertical integral length scale, and the coherent pressure rollers characteristic of shear layers undergo transient realignment towards the direction orthogonal to mean shear, consistent with the long-time limiting planar shear layer. Numerical experiments using fictitious test cases indicate that these effects are primarily driven through misalignment in the mean flow, and that the two orthogonal flow components in the mean shear frame are only weakly coupled.