MOVING SURFACE BOUNDARY-LAYER CONTROL AS APPLIED TO 2-DIMENSIONAL AIRFOILS

The concept of moving surface boundary-layer control, as applied to a Joukowsky airfoil, is investigated through an experimental program complemented by a flow visualization study. The moving surface was provided by rotating cylinders located at the leading edge and upper surface of the airfoil. The results suggest that the leading-edge rotating cylinder effectively extends the lift curve without substantially affecting its slope, thus increasing the maximum lift and delaying stall. When used in conjunction with a second cylinder on the upper surface, further improvements in the maximum lift and stall angle are possible. The maximum coefficient of lift realized was around 2.73, approximately three times that of the base airfoil. The maximum delay in stall was around 48 deg. In general, the performance improves with an increase in the ratio of cylinder surface speed U(c) to the freesteam speed U. However, the additional benefit derived progressively diminishes with an increase in U(c)/U and becomes virtually negligible for U(c)/U > 4. There appears to be an optimum location for the cylinder at the upper side of the leading edge that gave quite promising results. Although the C(L,max) obtained was a little lower than the two-cylinder configuration (2.35 against 2.73), it offers a major advantage in terms of mechanical simplicity.