Volumetric Velocimetry of Complex Geometry Effects on Transonic Flow over Cavities

Volumetric measurements of the flow within four cavities were made by scanning stereoscopic particle image velocimetry at a freestream Mach number of 0.8. The cavities have a length-to-depth ratio L/D = 7, and a width-to-length ratio b/L = 0.5. Three complex cavity geometries are used to model features representative of real aircraft bays and compare them to a simple rectangular cavity. The rectangular configuration exhibits signs of a transitional cavity regime, with resonant tones that compare well with predicted Rossiter values. The addition of a leading-edge ramp lofts the cavity mixing layer and accelerates the cavity freestream, resulting in reduced Rossiter amplitudes and increased frequencies. Side-wall spillage vortices are present in the rectangular cavity but are not found after the addition of side ramps that lessen the pressure gradient forming them. A center scoop causes a spanwise variation of velocity characteristics within the flowfield. Finally, a jagged leading edge attached to the scooped case results in reduced velocity fluctuations with an increased Rossiter mode-2 amplitude.