BOUNDARY-LAYER AND PRESSURE MEASUREMENTS ON A CYLINDER WITH UNSTEADY CIRCULATION CONTROL

Unsteady boundary-layer and surface pressure measurements were made on a circular cylinder with time-varying blowing applied from a narrow s panwise slot. The effects of mean blowing level, blowing frequency, an d boundary-layer trip location were examined at a Reynolds number of 2 .2 x 10(5) based on cylinder diameter. Time-resolved pressures were re corded using pressure sensors located on the Coanda surface and around the circumference of the cylinder. Flush-mounted hot film probes were positioned both upstream and downstream of the slot to provide a qual itative measurement of the boundary-layer characteristics. The results have shown that the shear stress just downstream of the slot was alwa ys in-phase with the plenum pressure. However, increasing reduced freq uency generally resulted in increasingly larger phase lags between the application of blowing and the development of the flow over the remai nder of the Coanda surface. For both steady and unsteady blowing, the jet entrained the outer flow at the slot and remained attached to the Coanda surface, provided a fully attached laminar or turbulent boundar y layer was obtained just prior to reaching the slot.