Active Control of Flow Separation from Supercritical Airfoil Leading-Edge Flap Shoulder

Abstract

Zero-net mass-flux periodic excitation was applied at the leading-edge flap shoulder of a simplified high-lift airfoil to delay flow separation. The term simplified infers that no slat or Fowler flaps are used. The NASA energy efficient transport supercritical airfoil was fitted with a 15% chord simply hinged leading-edge flap and a 25% chord simply hinged trailing-edge flap. Initially, the cruise configuration data from previous experiments were reproduced. The effects of leading- and trailing-edge flap deflections on the airfoil integral parameters were quantified. Detailed flow features were measured to identify optimal actuator placement. The measurements included steady and unsteady model and tunnel wall pressures, wake surveys, arrays of surface hot films, flow visualization, and particle image velocimetry. Eventually, high-frequency periodic excitation was applied to delay the occurrence of leading-edge flap shoulder stall and increased the maximum lift by 10‐15%. Low-frequency amplitude modulation was used to reduce the oscillatory momentum coefficient by roughly 50% with similar aerodynamic performance gains. It is demonstrated that the efficacy of the amplitude-modulated excitation is due to the generation of low-frequency motion, which is amplified by the separating shear layer.