Trailing-edge separation control on an aerofoil in low-speed flow

Low-speed wind-tunnel experiments have been performed with a laminar aerofoil. Loudspeakers mounted inside the wing generate an oscillating cross-flow through a spanwise slot in the upper surface of the aerofoil. The interaction of the oscillating flow with the flow over the aerofoil generates spanwise vortices. They enhance mixing and thereby add momentum to the region near the wall, so that boundary layer separation can be delayed, or a separated flow can be forced to reattach. The experimental results show that the maximum angle of attack of the aerofoil can be increased and lift forces can be enhanced by 10%.