We have been working on the problem of supersonic cavity flows, which are characterized by violent self-sustaining flow oscillations generating strong vortical motions, with a hope that such vortical motions can be used as a powerful means for supersonic mixing/combustion enhancement, a key technology for developing scramjet engines. In our previous study, we examined the generation and propagation processes of compression waves to clarify the feedback mechanism sustaining the oscillation. In the present study, focusing on the effect of the cavity length to depth ratio L/D on the oscillation frequency, we first examine the receptivity process by which the vortical disturbance dominating the cavity oscillation is generated by compression waves in the cavity leading edge region. We next derive and propose a new formula for the oscillation frequency, which expresses the resonance condition between the key phenomena such as generation, propagation and receptivity processes of compression waves governing the feedback mechanism.

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