Active control of separation from the flap of a supercritical airfoil

Zero-net-mass-flux periodic excitation was applied at several regions on a simplified high-lift system to delay the occurrence of flow separation. The NASA Energy Efficient Transport supercritical airfoil was equipped with a 15% chord simply hinged leading-edge flap and a 25% chord simply hinged trailing-edge flap. Detailed flow features were measured in an attempt to identify optimal actuator placement. The current paper describes the application of active separation control at several locations on the deflected trailing-edge flap. High- and low-frequency amplitude modulation of the high-frequency excitation were used for control. It was noted that the same performance gains were obtained with amplitude modulation and required only 30% of the momentum input required by pure sine excitation. Extreme sensitivity was found to the excitation location where the flap is highly curved. This sensitivity was reduced when using low-frequency amplitude modulation due to the long wavelengths generated by the excitation. It was found that for large flap deflections the majority of the lift increasing alteration of the surface pressures results from an upstream effect. Preliminary results of combining the excitations from leading- and trailing-edge devices are also presented.