Receptivity to Harmonic Excitation Following Nonimpulsive Start for Boundary-Layer Flows

Abstract

It has been shown in recent times that transition to turbulence occurs following two- and three-dimensional routes primarily by what is called the spatiotemporal wave front, for the canonical problem of a zero-pressure gradient boundary layer excited harmonically at the wall following an impulsive start. This paper shows that this onset process of disturbance growth continues also for a varying range of nonimpulsive wall excitation onset that is switched on smoothly. This is important because this will dispel any idea that a spatiotemporal wave front is totally due to impulsive start of wall excitation. This paper distinguishes between high- and low-frequency excitation cases to follow qualitatively different transition routes.