Wind tunnel experiments on unsteady cavity flow at high subsonic speeds

Abstract

Wind tunnel experiments have been done on the unsteady flow over a cavity system at high subsonic speeds. The investigation is part of an experimental program on the interaction between sound waves and two-dimensional transonic flows. The purpose of the present experiments is to examine whether the sound field radiated by the cavity system would be suitable for such interaction studies. The tests were performed on a two-dimensional cavity system consisting of a rectangular gap connected with a resonance chamber. The measurements have been performed in a Mach number range from 0.4 to 0.85. The investigation involved schlieren- and shadowgraph observations as well as meaaurements of the frequency and intensity of the radiated field. Periodically fluctuating flows can be characterised by their feed back mechaniam. In the present tests the pressure related to the resonance chamber oscillations is the feed back force. This results in a relatively simple and clean cavity flow. The cavity behaves - at some distance - like an acoustic monopole and emits intense acoustic radiation. The radiated sound field in general meets requirements concerning two-dimensionality and variability of frequency and intensity.