Flow Reattachment Using Synthetic Jet Actuation on a Low-Reynolds-Number Airfoil

Wind-tunnel experiments are used to study the effect of momentum coefficient and excitation frequency on flow separation using synthetic jet actuation. Experiments are conducted on a NACA 0025 airfoil at a chord-based Reynolds number of 100,000 and angle of attack of 10deg. The actuator is located near the leading edge, downstream of the mean separation location. High-frequency excitation is able to reattach the flow and eliminate the large-scale vortex shedding in the wake, leading to a decrease in drag of approximately 45%. Low-frequency excitation is employed to target the instabilities associated with the separated shear layer and vortex shedding in the wake. Excitation of the wake instability also causes the flow to reattach; however, it leads to organization of the large-scale vortex shedding. By forcing the boundary layer at the frequency of the shear-layer instability, the threshold momentum required to reattach the flow is an order of magnitude smaller as compared with high-frequency excitation, and the large-scale vortex shedding is suppressed.