Interactions Between Shock and Acoustic Waves in a Supersonic Inlet Diffuser

The interactions between shock and acoustic waves in a supersonic inlet diffuser are investigated numerically. The model treats the viscous flowfield in an axisymmetric, mixed-compression inlet operating under supercritical conditions. It is solved by means of a finite-volume approach using a four-stage Runge-Kutta scheme for temporal derivatives and the Harten-Yee upwind total-variation-diminishing scheme for spatial terms. Various distinct flow structures, including shock/boundary-layer and shock/shock interactions, are studied under the effects of externally imposed pressure oscillations at the diffuser exit over a wide range of forcing frequencies and amplitudes. As a result of the terminal shock oscillation induced by the impressed disturbances and the cyclic variation of the oblique/normal shock intersection, large vorticity fluctuations are produced in the radial direction. The characteristics of the shock/boundary-layer interactions (such as the size of the separation bubble, the terminal shock configuration, and the vorticity intensity) are also greatly influenced by the acoustic-driven shock oscillation. The overall response of the inlet aerodynamics to acoustic waves can be characterized by the mass-transfer and acoustic-admittance functions at the diffuser exit. Their magnitudes decrease with increasing frequency. A supersonic inlet acts as an effective acoustic damper, absorbing disturbances arising downstream. Severe flow distortion, however, may arise from shock oscillation and subsequently degrade the combustor performance.

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