A strange instability with growth normal to a boundary layer

Abstract

We present recent results concerning the linearized inviscid stability and propagation characteristics of disturbances to the boundary-layer flow due to an infinite rotating disk in otherwise still fluid. Such disturbances are expected to decay exponentially outside the boundary layer, but we have found a situation where exponential growth can occur in the wall-normal direction. It is shown, by considering the solution to the initial-value problem, that this behaviour can be predicted by using modes with exponentially divergent eigenfunctions. © 2006 Springer.