The effects of an oscillating flap and an acoustic resonance on vortex shedding

Vortex shedding from the blunt trailing edge of a flat plate spanning a wind tunnel under two kinds of periodic excitation is described. The conditions under which these two forms of excitation, an oscillating flap and an acoustic resonance, cause the vortex shedding to be in phase along the span are compared. Particular attention is paid to cases when the natural shedding frequency and either the flap frequency or the centre frequency of the acoustic resonance, respectively, are not quite coincident.