Instability of a smooth shear layer through wave interactions

Abstract

Wave interaction theory can be used as a tool to understand and predict instability in a variety of homogeneous and stratified shear flows. It is, however, most often limited to piecewise-linear profiles of the shear layer background velocity, in which stable vorticity wave modes can be easily identified and their interaction quantified. This approach to understanding shear flow instability is extended herein to smooth shear layer profiles. We describe a method, by which the stable vorticity wave modes can be identified, and show that their interaction results in an excellent description of the stability properties of the smooth shear layer, thus demonstrating the presence of the wave interaction mechanism in smooth shear flows. We wish to acknowledge the support of the Helmholtz Association (PACES II) and the Alexander von Humboldt Foundation fellowship to A.G. We also thank Subhajit Kar for help and two anonymous reviewers for their insightful comments.