Experimental Investigation of Flow Separation Control over Airfoil by Upper Surface Flap with a Gap

Abstract

This paper focused on the effects of the flap with a tiny gap on the flow separation over the NPU-WA-180 airfoil. The effects of the geometric parameters of the flaps, such as the flap gap height, angle, and position, were investigated. The study showed that the flap can significantly improve the stall features of airfoil in a limited phase of angle of attack (AoA), and increase lift and reduce drag at a high AoA. It can increase the lift coefficient and drag coefficient in the case of high AoAs, and the angle range of the lift augmentation and drag reduction can reach more than 9°. Furthermore, an excessively large gap is not conducive to the improvement of the airfoil stall performance. The flap angle plays a key role in the airfoil stall characteristic. As the flap angle decreases, the angle range of improving airfoil stall characteristics becomes larger, the pitching moment increment becomes smaller. However, the maximum lift increment and the effect of the drag reduction will decrease. And the effects of the position of the flap on the airfoil performance were also studied. Considering the maximum lift coefficient and drag coefficients in large AoA, the Type1 installed at the 0.7c position has the best effect; from the perspective of delayed stall, the Type1 installed at the 0.6c position has the best delay effect. These results can provide the data and theoretical support for the flap application in engineering.