Hysteresis behavior of shock train driven by continuous incoming Mach number variation in an isolator with background waves

Shock train hysteresis was investigated through wind tunnel experiments and numerical simulations of the internal flow in a supersonic isolator under background waves generated by a 14° wedge. An adjustable Laval nozzle was developed so that the throat area could be continuously changed and the incoming Mach number was varied between 1.8 and 2.4. Under the continuous decrease of the incoming Mach number, the impingement points of the background waves are observed to move uniformly upstream and the pressure of the relaxing boundary layer that is not swept by the impingement point decreases linearly. The pressure in the region that is swept by the impingement point first undergoes an adverse pressure gradient that results from the presence of the background wave, and then undergoes the favorable pressure gradient in the relaxing boundary layer. Hysteresis occurs when the shock train moves near the impingement point of the background wave, which is an inherent property of a bistable system. The triggering factor of the bistable system is that the adverse pressure gradient region that results from the background wave/boundary layer interaction cannot resist the pressure rise generated by the shock train leading edge, and the shock train can only stabilize upstream or downstream of the impingement point of the background wave. The maintenance factor of the bistable system is that the two positions of the shock train upstream and downstream of the impingement point of the background wave can match the same backpressure.