EFFECTS OF PERIODIC EXCITATION ON TURBULENT-FLOW SEPARATION FROM A FLAP

The effects of periodic perturbations on delaying separation or promot ing reattachment of initially separated Bow were experimentally invest igated. The leading parameters affecting the Bow are the flap deflecti on, the input momentum, and its reduced frequency. The sensitivity of the Bow to the imposed oscillations depends on its initial state, and this leads to hysteresis with respect to changes in any of the aforeme ntioned parameters. For example, the most effective frequency required to attach the Bow to the surface is much lower than the one required to prevent its separation. The amplitude needed to force reattachment may be an order of magnitude larger than the amplitude required to pre vent separation at a given inclination of the flap. Nevertheless, peri odic forcing is much more effective than steady blowing for boundary-l ayer control.