The dynamic evolution of a highly underexpanded transient supersonic jet at the exit of a pulse detonation engine is investigated via high-resolution time-resolved schlieren and numerical simulations. Experimental evidence is provided for the presence of a second triple shock configuration along with a shocklet between the reflected shock and the slipstream, which has no analog in a steady-state underexpanded jet. A pseudo-steady model is developed, which allows for the determination of the postshock flow condition for a transient propagating oblique shock. This model is applied to the numerical simulations to reveal the mechanism leading to the formation of the second triple point. Accordingly, the formation of the triple point is initiated by the transient motion of the reflected shock, which is induced by the convection of the vortex ring. While the vortex ring embedded shock move essentially as a translating strong oblique shock, the reflected shock is rotating towards its steady-state position. This results in a pressure discontinuity that must be resolved by the formation of a shocklet.

中文翻译：

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强入射冲击波引起的瞬态超音速尾随射流的动态演化

通过高分辨率的时间分辨波形和数值模拟，研究了脉冲爆震发动机出口处高度过度膨胀的瞬态超音速射流的动态演变。实验证据提供了第二种三重冲击配置以及反射冲击和滑流之间的冲击波，在稳态膨胀不足射流中没有类似物。建立了拟稳态模型，该模型可确定瞬态传播斜向冲击波的震后流动状况。该模型应用于数值模拟，以揭示导致第二个三重点形成的机理。因此，三点的形成是由涡流环对流引起的反射冲击的瞬态运动引起的。虽然涡流环嵌入的震动本质上是作为平移的强斜波震动而运动，但反射的震动正在朝其稳态位置旋转。这导致压力不连续性，必须通过形成冲击波来解决。