On the instability of Stokes layers at high Reynolds numbers

Abstract

The inviscid instability of Stokes layers is investigated. The Stokes layer is shown to support inviscid Floquet modes at sufficiently high values of the disturbance wavenumbers. Other non-Floquet modes are investigated and are shown to be the likely cause for instability in Stokes layers. These modes intersect with a viscous continuous spectrum of disturbances and it is this interaction which enables free-stream disturbances to penetrate into the boundary layer and amplify exponentially. The relevance of the inviscid theory to previous viscous instability calculations for Stokes layers is discussed.