Application of piezoelectric actuators at subsonic speeds

An experimental study has been conducted to investigate the effects of using a series of piezoelectric actuators at two chordwise positions (25 and 50% chord length) on a NACA 0015 aerofoil at subsonic speeds. The lift and drag forces were measured using a three-component force balance. A detailed boundary-layer survey was carried out using hot-wire anemometry. The actuators operating at 25 % chord length are more effective, resulting in an increase of the lift-to-drag ratios at higher frequencies. Boundary-layer surveys indicated that, with the actuators operating at 25% chord length, the boundary-layer thickness is drastically reduced downstream of their location, whereas the flow remains mostly undisturbed in the upstream direction. The actuators can fix laminar to turbulent transition and eliminate the laminar separation bubble at lower Reynolds numbers.