Flutter suppression of thin airfoils using active acoustic excitations

Abstract

A theoretical analysis of the flutter suppression of oscillating thin airfoils using active acoustic excitations in incompressible flow is presented. Closed-form unsteady aerodynamic loads induced by a simple harmonic acoustic excitation on a typical section model are derived. The acoustic wave generator used in the present flutter suppression analysis is activated by a state feedback control law that particularly takes into account the relative phases between the sensed states and the acoustic excitations. The flutter boundaries of the typical section, with and without the acoustic excitations, are evaluated using both the V-g and root-locus methods. The results show that, although the acoustic wave is a weak flow perturbation per se, the induced aerodynamic loads can be large enough to be employed as the flutter control forces. The circulatory part that makes the flow satisfy the Kutta condition at the trailing edge contributes the most to the magnitude and phase of the acoustically induced airloads, in particular when the acoustic excitation position is placed close to the trailing edge. Parametric study reveals that both the phase of the feedback gain constant and the acoustic excitation position are critical for the present new flutter suppression technique.