Effect of Planform Aspect Ratio on Flow Oscillations in Rectangular Cavities

Abstract

An experimental investigation was undertaken to examine the effect of cavity lateral width on the flow oscillations that occur in an open cavity placed within a turbulent subsonic boundary layer. A rectangular cavity with a length to depth ratio L/D=1 and planform aspect ratio L/W=0.115 was placed within a thick turbulent boundary layer with a corresponding Reθ=10.5×103. Pressure time histories were acquired at six separate cavity widths (or L/W values) using microphone-type pressure transducers. The spectral character of these signals was analyzed and the pressure levels and dominant frequencies determined. This study indicates that large changes in the pressure level occur as L/W varies from 0.115 to 0.682. A state of fluid dynamic resonance was observed at L/W=0.137 and fluid–acoustic resonance at L/W=0.682, the smallest cavity width. Relative sound pressure level calculations indicate that the energy within the cavity compared with that of the boundary layer, was observed to increase by approximately 40 percent at L/W=0.137. [S0098-2202(00)00601-5]