Active Flow Control for High Lift Airfoils: Dynamic Flap Actuation

Abstract

An extensive series of small-scale wind tunnel tests was conducted at the Illinois Institute of Technology as part of the Boeing/DARPA/AFRL/NASA-sponsored ADVINT program. Various methods of Active Flow Control (AFC) were applied to a high-lift airfoil with a highly-deflected simple flap. The major goal of the program is to significantly increase aerodynamic performance during takeoff and landing by utilizing an affordable, easily maintainable simplified flap system that relies on AFC to control separation at high flap deflections, and enables the development of next generation extreme short takeoff and landing (XSTOL) transport aircraft. A small but important subset of these tests, presented here, investigated unsteady flap effects on the performance of the AFC system. The model was modified to allow dynamic deflection of the simple flap at controlled rates. The primary objective of this test series was to investigate the effectiveness of AFC applied to the simple flap as it deflects from a high-drag to a high-lift deflection angle as part of a conceptual takeoff maneuver for future XSTOL aircraft. By studying the behavior of the pressure coefficient at key locations on the airfoil under these unsteady flow conditions, it was found that the lift enhancement due to the effective control of flow separation and globalcirculation enhancement for the static-flap case, is also realized when the same control is applied to a dynamically deflecting flap, and that the AFC performance is generally independent of flap deflection rate. However at high deflection angles, when the flap transitions to a flow regime where the AFC system can no longer maintain separation control, any local flow effects of the AFC that develop on the static flap may be lost during the dynamic flap deployment.