Dynamic characteristics of shock wave propagation in an expanded duct influenced by downstream throttling

In this article, the shock wave propagation in an expanded duct affected by downstream throttling at different positions is investigated. Fast-response transducers and schlieren visualization with a high-speed camera were employed to capture dynamic pressures on walls and shock interaction patterns, respectively. The results demonstrate that the characteristics of shock train motion can be strongly affected by throttling position. In the long model, where throttling device is mounted downstream away from nozzle exit, shock train moved upstream nearly linearly with the increasing in throttling, while in the short model, where throttling device is mounted at the nozzle exit, the shock train experienced downstream motion and upstream motion in turn during continuously increasing throttling. The evolution of shock interaction in the long model changed smoothly, while shock interaction in the short model is characterized by RR-to-MR transition and symmetry-to-asymmetry switching. Shock polar lines indicate that the local pressure ratios in both models show the same tendency which increases with throttling increasing. Therefore, the complex propagation of shock train in the short model still holds a monotonic change of local pressure ratio to respond to downstream disturbance.