Post-Stall Lift Enhancement of a Flat Plate Airfoil by Suction

Abstract

The effect of suction on airfoil surface at various locations downstream of the leadingedge of a thin flat-plate airfoil was studied in a wind tunnel at a low Reynolds number. At post-stall angles of attack, substantial lift enhancement and delay of stall can be achieved if a large separation bubble is generated by reattaching the massively separated flow near the trailing-edge. The effects of location and volumetric flow rate of suction were investigated by means of force and velocity measurements. There is an optimal location of suction around x s /c = 0.4, which generates the maximum lift coefficient for suction coefficients less than 3%. When suction is applied near the leading-edge, it may be easier to reattach the flow for small suction coefficients, but the resulting small separation bubble causes smaller lift increase. The size of the separation bubble is important, and small bubbles can even cause smaller lift enhancement than the separated flows due to the suction further downstream.