Effect of planform aspect ratio on flow oscillations in rectangular cavities

An experimental investigation was undertaken to examine the effect of cavit y lateral width on the flow oscillations that occur in an open cavity place d within a turbulent subsonic boundary layer. A rectangular cavity with a l ength to depth ratio L/D = 1 and planform aspect ration L/W = 0.115 was pla ced within a thick turbulent boundary layer with a corresponding Re-theta = 10.5 x 10(3). Pressure time histories were acquired at six separate cavity widths (or L/W values) using microphone-type pressure transducers. The spe ctral character of these signals was analyzed and the pressure levels and d ominant 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 flui d dynamic resonance was observed at L/W = 0.137 and fluid-acoustic resonanc e 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].