Effects of an Oscillating Flap on the Main Airfoil Unsteady Lift in Grid Turbulence

A wing of NACA 0015 profile and Aspect Ratio 2.4 fitted with a Trailing Edge Flap was tested in a wind tunnel for both smooth and turbulent flow conditions at a Re number 108000. The unsteady lift on the wing was measured with and without the flap. Two types of flap excitation were tried: One was of the “open loop” type in which the flap was subjected to sinusoidal pitching oscillations while the wing was set to a constant angle of attack. In the second, “closed loop” mode, the excitation signal fed into the flap originated from the unsteady lift of the wing itself. The phase lag between those signals was changed and it was found that it played a significant role in the suppression of the main wing unsteady lift.