Lift Enhancement of a Flat-Plate Airfoil by Steady Suction

The effect of suction on an airfoil surface at various locations downstream of the leading-edge 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 field measurements. There is an optimal location of suction around xs /c = 0.4, which generates the maximum lift coefficient for suction coefficients less than 3%. When suction is applied closer to the leading-edge, it may be possible to reattach the flow for smaller suction coefficients, but the resulting small separation bubble causes smaller lift increase. Large separation bubbles are needed for the maximum time-averaged lift enhancement, however they exhibit shear layer flapping, intermittent reattachment, and larger lift fluctuations.