Internal accoustic excitation to enhance the airfoil performance at high reynolds number

The ability to force air flow to follow the contour of a given lifting surface, even under the adverse pressure flow gradient, plays a significant role in optimizing the performance of lifting surface. As the angle of attack (a) increases large portion of the lifting surface will not see the flow due to the separation occurring closer to the leading edge. This creates an unsteady wake which results in loss of lift and increase in drag. In order to minimize the boundary layer separation, additional energy must be given to a low momentum fluid in the very near-wall region. It has been found that acoustic-vibration energy, which introduces periodic energy input, delays flow separation. The approach presented herein employs acoustic and vibration excitation. Two designs were constructed and experimented upon using the 0.76 m open jet open circuit subsonic wind tunnel at the University of New South Wales, with results showing potential to reduce flow separation. In the present study, speakers were used as means of internal excitation to vibrate the NACA 0015 wing. Various frequencies were applied on the top surface of the wing by the internally attached speakers. When the flow was excited at a favourable frequency, the flow separation was suppressed, and delay in stall angle of attack (α_stall) was found to occur. Further, the relationship between the excitation frequencies (f_e), shedding frequencies (f_s) and the Strouhal numbers (Sr) was found.