On the unsteady, wake induced lift on a slotted airfoil

Abstract

A theoretical model is examined to determine the influence of a slot in a thin airfoil on the unsteady lift caused by vortices shed into the wake. It is shown that at sufficiently low reduced frequencies based on the width of the slot, vorticity production at the edges of the slot can prevent penetration by the unsteady flow so that the airfoil behaves as if the slot were absent. There exists a range of frequencies, however, in which the magnitudes of both the lift and the accompanying radiated sound can be significantly reduced relative to their respective levels for the unslotted airfoil.