Acoustic control of flow over NACA 2415 aerofoil at low reynolds numbers

Abstract

Within the concept of this study, first low Reynolds number flow phenomena, including laminar separation bubble (LSB) and stall were explained. Then a literature review on the acoustic flow control was presented in three categories: flow control with constant frequency, flow control with constant amplitude, and flow control with variable frequency and amplitude. Aside from the review part, results of a comprehensive experimental study on the effects of acoustic flow control at low Reynolds numbers were presented. Within the scope of this experimental study, the effects of both parallel and perpendicular acoustic flow control were examined by means of pressure measurements, force measurements, hot-wire anemometry, flow visualization, and particle image velocimetry (PIV). In order to establish a baseline data, all of the measurements were first applied for the no control case. The effects of acoustic control were examined especially on the characteristics of LSB and stall. It was found that the acoustic excitation can be employed to decrease the height and length of LSB leading to increased lift coefficient and decreased drag coefficient. Also, acoustic flow control increased the angle of stall. It was also seen that the effective excitation frequency increases also, but the range of Zaman number (St/Re0.5) based on effective frequency still is approximately same with increasing Reynolds numbers. Finally, it was shown that the general aerodynamics performance of an aerofoil at low Reynolds numbers can easily be enhanced by employing acoustic flow control, and the parameters of the acoustic flow control can easily be adjusted in order to keep up with the changing conditions of flow.