Airfoil flow separation control with plasma synthetic jets at moderate Reynolds number

An array of 26 plasma synthetic jet actuators (PSJA) is flush-mounted on a NACA-0015 airfoil model to control the leadingedge flow separation at moderate Reynolds number (Re c = 1.7 x 10 5). The stall angle of this airfoil is postponed from 15.5. to approximately 22., and the peak lift coefficient is increased by 21%. PSJAs exhibit distinctive separation control mechanisms depending on the relative location between actuation and separation and reduced frequency of actuation (F *). At an angle of attack of = 15.5., the non-actuated flow separates approximately 4% chord length downstream of the jet orifices. Plasma synthetic jets (PSJs) applied at F * = 0.5 can displace the separation point downstream to mid-chord position, as a result of the energizing of the incoming boundary layer through mixing enhancement. As a comparison, with actuation frequency of F * = 0.25, the separation point at = 15.5. remains near the leading edge and the zero-velocity line is periodically swept towards the suction surface by the convecting spanwise vortices generated from PSJ actuation, leading to a reduction of timeaveraged backflow area. For the case of separation control at = 22., the separation point resides always upstream of the actuation position, regardless of actuation frequency. The peak lift coefficient is attained at F * = 1, and the decreasing lift at high actuation frequency (F * = 2) is ascribed to the severe interaction between adjacent spanwise vortices at short spacing. [GRAPHICS] .