Abstract:
Measurements have been made of the time average and unsteady pressures acting on the roof and behind a series of rectangular cavities set in the roof of the 2 ft x 1 1/2 ft transonic tunnel. It was found that the unsteady pressures contain both random and periodic components. The random component predominates in the shallower cavities (length/depth ratio > 4) and is most intense near the rear wall. The periodic component predominates in the deeper cavities (length/depth ratio < 4) and may form standing wave patterns. It is suggested that the periodic component is due to an acoustic resonance within the cavity excited by a phenomenon similar to that causing edge-tones. It may be suppressed by fixing a small spoiler at the front of the cavity.
