Numerical investigation on the forced oscillation of shock train in hypersonic inlet with translating cowl

To investigate the forced oscillations of shock train caused by sinusoidal backpressure perturbations with different amplitudes and frequencies in a hypersonic inlet equipped with translating cowl, numerical simulations have been conducted with the application of dynamic mesh method. The results reveal that under sinusoidal backpressure perturbations, the shock train oscillates and propagates upstream as the cowl moves downstream rather than crosses the shock-impact points abruptly with significant migration distance, compared to the result obtained under constant backpressure. Meanwhile, the amplitude of forced oscillation increases when the shock train leading edge oscillates around the adjacent shock-impact points. The larger amplitude of backpressure perturbation not only aggravates the forced oscillations but also increases the number of shock-impact points that the shock train crosses in one cycle, which leads to complicated changes in the shock train structures, even involving the separation mode transition. The frequency of forced oscillation equals to the one of backpressure perturbation invariably, but with certain phase lags due to the interference of background waves. Although the variable background waves do have the ability to affect the amplitude of forced oscillation, they are incapable of changing the frequency of forced oscillation.