Unsteady surface pressure and near-wake hot-wire measurements of a circulation control airfoil.

Abstract

The large lift coefficient changes attainable with Circulation Control Airfoils through small changes in boundary layer blowing suggest rotary wing cyclic control can be obtained through modulation of the blowing. Static pressure distributions were obtained to assess the unsteady behavior of a Circulation Control Rotor in a two-dimensional flow. A constant-radius hotwire wake traversing mechanism was constructed to augment the pressure data and to study the flow phenomena occurring in the region of Coanda jet separation. Through correlation of turbulence intensity data with the pressure data, it was discovered that the point of Coanda jet separation could be located using the hotwire. The objective of these tests was accordingly expanded to include correlation of the location of separation with flow parameter variation. Although steady flow, steady blowing tests results were favorable, the unsteady blowing test was restricted in scope because of an inability of the injection air compressor to provide an adequate flow, and because the real-time acquisition system was not completed in time for these tests. From mean value and RMS data obtained during oscillatory blowing, no increase in average lift augmentation above that produced in equivalent steady blowing was discernible.