Mechanism and prediction for occurrence of shock-train sharp forward movement

A numerical simulation was conducted using the commercial computational fluid dynamics software FLUENT to study the influence of inner flow structures on the motion characteristics of a separation oblique shock train caused by backpressure. Simulation results indicated there was a separation point of the boundary layer at the head of the shock train. The separated flow expanded in the isolator and led to movements of the shock train. With the shock train moving forward in the isolator, the leading edge of the shock train passed through the peaks and valleys of pressure along the forward path. As the pressure gradient at the separation point switched between positive and negative gradients, the state properties of the shock train movements transformed between a slow forward movement and a sudden sharp forward movement. The sudden sharp forward movement of the shock train always occurred when the separation point surmounted reflection points of the background wave system, which implies that the forward motion characteristics of shock train are related to the background flow structures. So, the occurrence of a sharp forward movement of the shock train can be predicted from the flow structures of a fully started state.