This paper is concerned with the mechanism of supersonic cavity flow oscillations. Open cavities exposed to high speed flows may cause self-sustaining oscillations and emit strong acoustic waves. Many researchers agree that the shear layer instability wave impinges on the cavity trailing edge and generates the acoustic wave, while the acoustic wave impinging on the cavity leading edge disturbs the shear layer to initiate the next cycle oscillation. On their actual generation processes, however, there has been almost no information in the literature. Based on our numerical simulation results for the case of two-dimensional flow over a rectangular cavity of L/D = 1 at Mach number 1.8 we have here described these processes and carefully examined the generation of compression wave to find that it is generated as soon as the crest of the instability wave has passed over the trailing edge. This is in contrast to Tam and Block's theoretical model where it is assumed to be radiated when the shear layer deflection is negative maximum. We thus try to improve the theoretical model and further consider several important points such as the leading edge receptivity and the effect of L/D for future studies to improve our understanding of the supersonic cavity oscillation mechanism.

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