Sound production by shock leakage in supersonic jet screech

Direct experimental evidence is presented for the shock leakage phenomenon occurring in an axisymmetric jet screeching in the A1 mode. Ultra-high-speed schlieren images are presented, filtered to only show upstream-travelling fluctuations. These visualizations are presented in parallel with an implementation of the geometrical acoustics model for shock leakage, developed by Shariff and Manning,¹ applied to phase reconstructed velocity data. The model shows remarkable agreement with the schlieren visualizations, predicting leakage to occur at the third and fourth shock cells, and the timing of the leakage to be such that constructive interference is produced in the upstream direction, as per the original theoretical model of Powell.