SEPARATION AND CIRCULATION CONTROL ON A THICK BLUNT ELLIPTICAL AIRFOIL

Abstract

Various methods of Active Flow Control (AFC) were 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. Steady blowing, steady suction and Zero Mass Flux Forcing (ZMFF) were applied to enhance the performance of the airfoil at all possible parts of the flight envelope. All three modes of actuation were two dimensional. The unique design of the model enabled one to vary the slot-widths, their locations and their orientations, without a change of hardware. Changes in the free stream velocity, amplitudes and frequencies of the periodic forcing, or mass flow associated with the steady suction or blowing were also investigated. Wedges attached to the trailing edge of the ellipse modified the shape and sharpness of the trailing edge thus determining the Kutta condition rather than letting it be freely established by the AFC. For steady blowing the increment of the lift coefficient scales with the momentum coefficient (C(μ)), provided that the slot is thin. The lift increment generated by the blowing is adversely affected by wider slots and a deleterious effect on C(L) was observed at low C(μ). The lift increment was independent of Reynolds numbers of the airfoil and the jet but it depended on the slot location and orientation. An imposed Kutta condition, even when carried out by a small protuberance had a significant effect on C(L). The drag was not necessarily reduced by the blowing and C(μ) was not its primary scaling parameter. 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 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.