Aerodynamic Control of Low-Reynolds-Number Airfoil with Leading-Edge Protuberances

This paper presents an experimental investigation of the control of airfoil aerodynamics at a low Reynolds number of 5 x 10(4) within a wide range of attack angle alpha using a leading-edge-protuberance technique. The essence of the technique is to manipulate flow around the airfoil by replacing the straight leading edge of a baseline airfoil with a sinusoidal wavy airfoil. Whereas the lift and drag forces and the lift-to-drag ratio were measured using a three-component force balance, the flow was mainly measured using a particle-image velocimetry. The sinusoidal protuberances effectively suppressed airfoil stall, and the corresponding aerodynamic performance was impaired to some extent. Meanwhile, control significantly improved the airfoil aerodynamics in the poststall alpha region, for example, 16 < alpha < 70 deg, leading to a maximum 25.0 and 39.2% increase in lift coefficient and lift-to-drag ratio, respectively, and a maximum 20.0% decrease in drag coefficient. The protuberances may influence control performance in a similar way with low-profile vortex generators. The flow physics behind the observations were discussed in detail.