Abstract
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 poststall 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 , 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.
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