Effects of back pressure perturbation on shock train oscillations in a rectangular duct

The nature of flow field inside the scramjet engine consists of shock-shock interaction and the shock boundary layer interaction. For a sustained combustion, a device called isolator plays a critical role in providing adequate pressure to the combustion chamber by a series of bifurcated shock waves called “shock train”. A small downstream pressure perturbation can cause upstream movement of this shock train and results in engine unstart condition. The propagation speed of downstream disturbance can influence the shock train oscillation. In the present study, computational fluid dynamics analysis is conducted to understand the oscillatory characteristic of shock train in a rectangular duct at M =1.75. The impact of downstream perturbation frequency (f b = 10 – 50 Hz) and the amplitude (A = 0.01 – 0.1) are simulated and discussed. The presence of low-frequency oscillation is observed without back pressure perturbation. The downstream pressure perturbation has a noticeable effect on the shock train excursion length i.e., the maximum upstream to downstream distance moved by shock train. The increase in perturbation frequency leads to decrease in disturbance propagation speed. Similarly, the propagation speed increases with the increase in the perturbation amplitude.