Experimental study on the forced oscillation of shock train in an isolator with background waves

Abstract

The forced oscillation of shock train in an isolator with background waves have been investigated in a direct-connect wind tunnel. High-frequency pressure measurements were used to obtain the pressure histories in experiment and high-speed Schlieren technique was used to capture the shock train motion. Two types of oscillations during forced oscillation were studied and presented in detail. The large separation zone induced by leading shock is always located on one wall during type I oscillation, and switches between two walls during type II oscillation. Type II oscillation is a new type of oscillation that has not been observed in the forced oscillation occurring in an isolator with uniform incoming flow until now. During type II oscillation, the oscillation range of shock train is much larger than during type I oscillation, which makes type II oscillation have a greater impact on the performance and operating boundary of scramjet. The effect of backpressure oscillation amplitude and frequency on the two types of forced oscillation were studied. It was found that the backpressure oscillation amplitude and frequency have a significant effect on type I oscillation, but have little effect on type II oscillation. When the backpressure oscillation amplitude increases or the oscillation frequency decreases, the oscillation range of type I oscillation increases. If the backpressure oscillation amplitude is low or the oscillation frequency is high, type II oscillation does not exist. However, once type II oscillation occurs, its oscillation range does not change with the changes of backpressure oscillation amplitude and frequency. Finally, the different mechanisms of two oscillations were discussed. Type I oscillation is caused by backpressure perturbation and type II oscillation is caused by background waves.