Experimental Investigation of Bio-Inspired High Lift Effectors on a 2-D Airfoil

Abstract

Flaps mounted on the upper surface of an airfoil, called Lift Enhancing Effectors, have been shown to increase maximum lift and stall angle in wind tunnel tests. These effectors are fabricated from 0.35mm thick Mylar and are allowed to rotate freely about their leading edge. The tests were done in the NCSU Subsonic Wind Tunnel at a chord Reynolds number of 4 10 5 . The maximum lift coefficient was increased by up to 30% and stall was increased from 12o to at least 16o. Fabricating the effector out of stiff wood and fixing the deployment angle with respect to the airfoil surface caused the zero lift angle of attack to increase in proportion to the deployment angle. Drag tests on both the free-moving and fixed deployment effectors showed marked improvement in drag at high alpha. The fixed deployment angle effectors showed drag improvement at increasingly higher alpha as deployment angle was increased. Oil flow visualization was completed on the clean airfoil and the fixed deployment angle effectors. The surface flow pictured by these oil flow tests proved that the effector causes the separation point to move aft on the airfoil, as compared to the clean airfoil. This is thought to be the main mechanism by which the effectors improve both lift and drag. Finally CFD simulations were run and compared to the oil flow visualization. Results for separation point agree between oil flow and CFD, for most alphas. Lift tests indicate that increasing the deployment angle past 60o amounts to very little improvement in Cl. Drag tests show that the free-moving effector naturally produces a drag curve in between the curves for the 30o and 45o fixed effectors.