Effect of acoustic excitation on stalled flows over an airfoil

The effect of acoustic excitation on poststalled flows over an airfoil, i.e., flows that are fully separated from near the leading edge, is investigated. The excitation results in a tendency toward reattachment, which is accompanied by an increased lift and reduced drag, although the flow may still remain fully separated. With increasing excitation amplitude, the effect becomes more pronounced but shifts to a Strouhal number that is much lower than that expected from linear, inviscid instability of the separated shear layer