Experiment Demonstrating Reduction of Dynamic Stall by a Back-flow Flap

A back-flow flap attached to the suction side of an airfoil is investigated in both passively and actively actuated modes for the control of dynamic stall. Experiments in a low-speed wind tunnel at 50 m/s were used to characterise the reduction in dynamic stall using pressure measurements on the midline of an airfoil. The pitching moment peak is reduced by an average of 25% for all deep stall test cases for active actuation of the flap, while for passive actuation the pitching moment peak is reduced by 19%. In each case the maximum lift remained the same, while the peak drag increased by an average of 2.5% for the active flap, and by 0.9% for the passive flap. With the flap closed at low angles of attack, the reference values of the airfoil are retained.