Suppression of Pressure Oscillations in High-Mach-Number, Turbulent, Cavity Flow

Abstract

Fluctuating wall pressure measurements have been made in a high-Reynolds-number, Mach 5, turbulent cavity flow. The cavity length to depth ratio was varied from 3 to 5 with a fixed width to depth ratio of 3. Slotted and vented upstream and downstream walls, slanted downstream walls (inclined in either the streamwise direction only or inclined streamwise and swept spanwise), and spoiler and vortex generator arrangements were used to explore their effectiveness at suppressing the pressure oscillations. In practice, wall geometry will be dictated by many constraints; thus, in the absence of a particular application, it is not meaningful to claim that one particular geometry is the most effective. However, consistent with work at lower Mach numbers, it is evident that certain slanted and swept downstream walls are quite effective, reducing the high mean pressure and rms pressure levels near the downstream wall/floor junction by 30-35% and 40%, respectively. At this high Mach number, the coupling between the shear layer dynamics and cavity acoustics is weak. As a consequence, the cavity mode frequencies, which are essentially independent of geometry changes, are in as good an agreement with closed-box frequency predictions as they are with the predictions of Rossiter's modified formula (Rossiter, J. E., Wind Tunnel Experiments on the Flow over Rectangular Cavities at Subsonic and Transonic Speeds, Aeronautical Research Council Reports and Memoranda, ARCR & M No. 3438, London, 1964).