Simulation and analysis on the motion characteristics of shock train under dynamic throttle

To investigate the shock train characteristics under the influence of dynamic backpressure, the dynamic throttle flows of a two-dimensional inlet/isolator configuration were simulated under Mach 6 free steam condition, where the throttle ratio increased from 0.20 to 0.32 and were kept constant. The effects of increasing time （varied from 1–10 ms） of the throttle ratio were analyzed. The results show that the amplitudes of the shock train downstream motion and the upstream motion are within 3 mm and about 18 mm, respectively, as the throttle ratio increases from 0.20 to 0.32 within 5 ms. The shock train motion lag behind the throttle process and the lag time decreases with the prolongation of the throttle variation time. When the increasing time of the throttle ratio was 6 ms and above, the shock train could move downstream to the middle of the cavity and the motion amplitude reached 31 mm, accompanied by flow oscillations. The upstream motion amplitude of the shock train was still about 18 mm and the shock train motion was approximately synchronized with the throttle process. The analysis showes that the lag of the shock train motion is related to the time intervals of back pressure increment and propagation, which is longer than the variation time of the throttle ratio under the condition of short increasing time. Under the long increasing time conditions, the flow oscillations are related to the increase of the mass flowrate in the subsonic section of the cavity, which dominates the shrinkage of the recirculating region in the cavity. This further causes the expansion of the supersonic flows near the cavity and generates choked flows near the throttle region. Therefore, flow oscillations are generated through the interactions between the separated shock wave flows of the choked flows and the cavity recirculating region. The lag of the shock train motion and its influence on flow performance should be considered in engineering design.