The dynamics of separation control on a rapidly actuated flap

Unsteady aerodynamic loads on a NACA 0021 airfoil during rapid flap deflections were investigated. Typical dynamic stall effects like an overshoot in lift, drag, and pitching moment have been observed. Flap deflection angle and speed were varied while the angle of attack remained constant at α = 0°. To prevent stall and accompanying detrimental behavior, fluidic actuators generating discrete sweeping jets were integrated into the simple flap of the airfoil. Initial experiments at various angles of incidence but constant flap deflections proved that these actuators can prevent flow separation, increase lift, and decrease the drag of the airfoil. Dynamic tests revealed that sweeping jet actuators can also eliminate dynamic stall effects. A significant gain in lift and a substantial reduction in drag were achieved within a short period of time, even for high flap deflection angles of 30°.