Active Flow Control Applied to High-Lift Airfoils Utilizing Simple Flaps

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. In these tests, Zero Mass Flux (ZMF) Active Flow Control (AFC) was applied to a high-lift airfoil with a highly-deflected simple flap. Three different leading edge geometries were evaluated, and the simple flap performance was compared to the performance of various slotted flap configurations. The wind tunnel model was tested in both 2-D and 3-D configurations. It was found that on this airfoil, flow separation near the leading edge occurred at low angles of attack with droop and cruise leading edges. This resulted in flow conditions upstream of the AFC location at the flap shoulder that were not amenable to effective control. The addition of a slat leading edge improved the upstream flow conditions and resulted in significant performance enhancement with AFC. The AFC applied at the flap shoulder effectively increased the circulation around the airfoil without fully reattaching the flap. The improvement in lift with AFC was found to be proportional to the ratio of peak ZMF jet velocity to the free stream velocity. It was determined that values of this ratio ≥ 2 were sufficient to meet the performance goals of the ADVINT program. It was also found that replacing the simple flap with a slotted flap provided even greater performance. Finally, it was found that 3-D effects did not diminish the effectiveness of the AFC, and near the tip, the AFC effects were even enhanced.