Analysis of Cavity Flow and The Effects of a Rod in Crossflow

• Main Author: Loewen, Richard David
• Published: Trace: Tennessee Research and Creative Exchange 2008
• Subjects: Aerospace Engineering
• Online Access: http://trace.tennessee.edu/utk_gradthes/463

Subsonic cavity flow tests of an L/D = 3.5 cavity, with three different diameter rods in crossflow, 1/8", 3/16", and 1/4", were conducted using the High Speed Wind Tunnel in the University of Tennessee Space Institute’s Gas Dynamic Laboratory. The average Mach number flow over the duration of the four phase testing sequence was 0.52, with a unit Reynolds number of 13.8 x 106. With the use of a dynamic pressure transducer and a laser PIV system, Spectral and Flow Visualization data was collected with aim of investigating the effect of the rods in crossflow on cavity flow. However, for reasons beyond the control of this investigation, a converging-diverging supersonic nozzle was used in place of a subsonic nozzle. As a result, the separated, or near separated, flow on the diverging side of the nozzle created a region of low kinetic energy flow approximately 5 mm above the floor of the tunnel test section. Despite the presence of this undesirable feature, the Baseline cavity, without a rod in crossflow, was found to resonate at 1413 Hz and produced an average peak amplitude tone of 148.7 dB SPL. The effect of placing different diameter rods in the crossflow was to reduce the amount, and intensity, of shear layer interactions, by helping to loft the flow over the trailing edge of the cavity. The best results were achieved with a 1/4" diameter rod, which, on average, provided 15.1 dB SPL of acoustic suppression. It was concluded that the suppression observed in this particular experiment was the result of blockage and lofting effects, which helped the shear layer to span the length of the cavity and reduce the intensity of the shear layer interactions at the trailing edge.