Active control of fluctuating pressure induced by blade-vortex interaction

It is well known that interactions between the leading edge of a blade and incoming vortical structures produce a sharp rise in fluctuating pressure nearby, contributing significantly to the noise production in various types of rotorcrafts. To suppress this fluctuating pressure and subsequently induced noise, as the first step, active control of interactions between an airfoil and incoming cylinder-generated vortices, which mimics the practical phenomenon, was experimentally investigated. The essence of the control is to create a local perturbation, using piezo-ceramic actuators, on the surface near the leading edge of the airfoil, thus modifying the airfoil-vortex interactions. Both open- and closed-loop methods were used, where the surface perturbation was controlled by an external sinusoidal wave and a feedback pressure signal from a pressure transducer installed at the leading edge, respectively. It was observed that the closed-loop control was superior to the open-loop one; the closed- and open-loop controls achieve a maximum reduction in the pressure fluctuation at the dominant vortex frequency by 32% and 11%, respectively. The detailed physics behind the observations was discussed.