Shock train structure in variable pressure condition

In this present study, a numerical computation is performed to investigate the effect of oscillation of nozzle pressure ratio (NPR) on shock train structure in a diverging duct. An overexpanded flow condition is considered where the shock-boundary-layer interaction produces a series of shock called 'shock train'. The result clearly shows that the internal shock train structure is dependent on the change of pressure ratio. Distinct shock train starting positions are observed with successive increasing and decreasing of pressure ratio even when at the same NPR during the oscillation. The location of reattachment point steps further downstream for upper wall relative to the lower wall, which expedite the asymmetric shock train formation. Irreversible behavior in the shock train length, shock train starting position and separation distance both in upper and lower wall are observed during this oscillation and all of them show hysteresis behavior.