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Separation Control on a Dynamic Trailing-Edge Flap
Research on control surfaces (flap, slat, entire airfoil) in motion has been done before and it was found, that a dynamic stall vortex develops which results in a higher lift as long as the control surface is moving. At the same time however, the drag significantly increases and a large nose down pitching moment occurs.
These effects of course occur as well when deflecting a flap, but stop immediately after the process of deflecting the flap is over and thus the motion stopped. The increase in lift is desirable (if it was steady) but the increase in drag and the pitching moment need to be prevented.
To investigate the dynamic stall, the post-stall separation and accompanying effects, a NACA0021 airfoil with a 30% simple flap was mounted in an open loop tunnel located in the aerolab at the UofA.
Fluidic actuators generating discrete sweeping jets were integrated in the flap shoulder. These devices have been proven to successfully prevent separation, increase lift and substantially reduce drag. Measuring the pressure over the surface of the airfoil and in the wake allowed to analyze and compare the flow behavior during a rapid flap deflection with and without active flow control. The experiments showed that a sufficient momentum input (cm) accomplished a prevention of the dynamic stall and thus the increase in drag and the quick pitching moment while at the same time the lift was increased significantly and stayed steady after the flap deflection. Even for high flap deflection angles of d=30° separation could be prevented using sweeping jet actuators.