Abstract: Force measurements combined with flow visualization are used to investigate the control of two dimensional leading-edge separation by means of flap oscillation. It is found that the results of control are related to the model natural flow patterns. When the natural flow pattern is a closed separation bubble, the excitation causes a lift loss. A reduction of reattachment length and a reduction of the drag of the model can be achieved by proper frequency excitation.The most effective Strouhal number range based on the reattachment length and the main stream velocity for drag reduction is 3-5. When the natural flow pattern is full separation, proper frequency excitation changes the flow field into a closed separation bubble and a lift increment is achieved. The most effective Strouhal number range based on the chord of the model and main stream velocity for lift increment is 0.70-2.5.

Key words: separation flow, control, experimental aerodynamics