Linear Mechanism of Wave Emergence from Vortices in Smooth Shear Flows

Abstract

A new linear mechanism of wave abrupt emergence from vortices in smooth shear flows is found. The phenomenon is closely related to non-normality of linear dynamics of disturbances in shear flows and is best interpreted in the framework of a nonmodal approach---by tracing of linear dynamics of spatial Fourier harmonics of vortex in time. Found phenomenon, demonstrated in the Letter for the simplest example of unbounded, compressible, plane Couette flow, should be important for numerous engineering applications and should be realized in various terrestrial and astrophysical shear flows.