Shear layer resonance over open cavities

Abstract

Self-sustained shear layer oscillations over open cavities beneath a laminar boundary layer were studied experimentally. The cavities were rectangular in cross-section. The research concentrated upon determining the effects of rotating the leading edge of the cavity relative to the flow direction. The leading edge was rotated from an initial position normal to the flow direction to angles up to 30 degrees from the normal. Measurements were performed in an open return wind tunnel with freestream velocities ranging from 20 to 44 m/s. The cavity depth was fixed at 6.35 mm and the streamwise length was varied from 6.55 to 13 mm. Constant temperature hotwue anemometers together with a dynamic signal analyzer were used to analyze the signals from the shear layer. For a particular cavity size, resonance frequency increased with increasing freestream velocity, while for a fixed freestream velocity as the cavity length was increased, the resonance frequency decreased. As the cavity was rotated, the resonance frequency gradually decreased. Due to inconsistent pattern no general relationship could be developed from the cross-correlation measurements.