On the parameters governing fluidic control of separation and circulaton

Active Flow Control (AFC) was experimentally investigated on an elliptic airfoil to improve our understanding of the flow mechanisms and identify the parameters, governing fluidic control of separation and circulation. Constant blowing, suction and Zero Mass Flux Forcing (ZMFF) were applied. The design of the model enables varying slot-widths, their locations and even orientations without resorting to machining, in addition to other parameters, such as free stream velocity, mass flow through the slots, flow control amplitude and frequency. Wedges attached to the trailing edge of the ellipse modified the shape and sharpness of the trailing edge thus changing the Kutta condition. It was found that for the constant blowing the increment of the lift coefficient scales with the momentum coefficient (C_μ), provided that the slot width is small. For wider slots the empirical correlation is proposed. A deleterious effect of steady blowing on C_L was observed at low C _μ. An imposed Kutta condition, even when carried out by a small protuberance has a significant effect on the lift, generated by stronger blowing. Suction is much more effective than blowing at low levels of C _μ. Neither C_μ , nor volume flow coefficient, C _Q, provides universal relation for suction. ZMFF is most effective in reattaching separated flow but the traditional <C_μ> does not provide the universal scaling for ZMFF. Much higher level of input was required to attach separated flow than to keep the flow attached.