Active Control of Separation on a Low Reynolds Number Airfoil Using Synthetic Jet Actuation

Wind tunnel experiments were used to study the effect of excitation amplitude and frequency on flow separation using synthetic jet actuation. A synthetic jet actuator was located near the leading edge of a NACA0025 airfoil at a chord-based Reynolds number of 100,000 and angle-of-attack of 10 degrees. Under these flow conditions, the boundary layer separated from the suction surface and failed to reattach. Low-frequency excitation was used to target flow instabilities, while high-frequency excitation was performed at time scales an order of magnitude smaller. Low-frequency excitation at the separated shear layer frequency was found to be the most effective technique for flow reattachment and drag reduction. The results suggested that flow reattachment depended on exceeding a threshold momentum coefficient that varied with excitation frequency. Furthermore, a local minimum in drag independent of excitation frequency was achieved when the momentum coefficient corresponded to an average jet velocity that matched the freestream velocity.