Active Control of Flow Separation on a Laminar Airfoil

Detailed investigation of the NACA 643−618 is obtained at a Reynolds number of 6.4×104 and an angle of attack sweep of −1≤α≤20 deg via particle image velocimetry and hot-film anemometry. The baseline flow is characterized by four distinct regimes, depending on angle of attack, with each exhibiting unique flow behavior. Active flow control via steady normal blowing is employed at four representative angles; blowing ratio (BR) is optimized by maximizing the lift coefficient with minimal power requirement. Suggestions are made with regard to the flow mechanisms whereby control is effective at each angle. A figure of merit is employed to quantify the efficiency of the actuation. The optimal BRs obtained at Reynolds number equal to 6.4×104 are kept constant to observe the scalability of the control with respect to Reynolds number, ranging over nearly two orders of magnitude. It is observed that this approach is nonideal and that the BR should be optimized with Reynolds number as well. The optimization procedure is repeated for two angles of attack at a Reynolds number of 4×106. Lift enhancement is maintained while reducing the power requirement, thereby increasing the efficiency of the flow control.