Volume 77 (2011) Issue 779 Pages 1522-1532
In order to clarify the generation mechanism of aerodynamic sound in cavity flows, aerodynamic sound and flow fields were simultaneously measured with a microphone and a high-speed flow visualization system. The effects of acoustic resonance on the flow and acoustic field were investigated by changing the cavity depth and free stream velocity. An expansion wave was found to be generated when a vortex collided with the downstream edge. This mechanism was independent of the oscillation mode of the cavity tone. Based on this generation mechanism, a new formula for the prediction of the frequency of the cavity tone was proposed. Also the effects of the ratio of the cavity length to the incoming boundary layer thickness on the cavity tone were investigated. As a result, it was shown that the oscillation mode became higher as the boundary layer thickness became thinner in comparison with the cavity length.