激波串与进气道肩部分离泡相互作用

Interactions Between Shock Train and Separation Bubble on Inlet Shoulder

关键词:  高超声速进气道  边界层抽吸  激波串  分离泡  耦合振荡

Key words:  Hypersonic inlet  Boundary layer suction  Shock train  Separation bubble  Coupled oscillation

摘要:

针对高超声速进气道激波串与肩部分离泡相互作用时的流动振荡问题，在来流马赫数为6的激波风洞中，采用高速纹影拍摄结合壁面动态压力测量，研究了有/无抽吸情况下激波串与肩部分离泡的相互作用过程。结果表明：当激波串前移至肩部附近时，有抽吸进气道也会产生大尺度的分离泡，进而有/无抽吸进气道内的激波串均会与肩部分离泡形成耦合振荡，并造成严重的脉动压力。在激波串的推动下，分离泡能够自由地越过肩部凸拐角，使得其自身的低频振荡特性能够显现。激波串内的压力波动会显著改变分离泡的形态，而分离泡形态的变化又会影响激波串内的压力，两者相互耦合从而维持这种低频振荡。无抽吸进气道具有相同的低频耦合振荡特性；而抽吸缝阻碍了上下游的信息传递，使得有抽吸进气道的分离泡低频振荡显著，而激波串振荡具有一定的宽频特性。经分离激波振荡范围和进气道入口速度无量纲后，有/无抽吸进气道低频耦合振荡的St均处于0.011~0.021，与经典分离泡的低频振荡特性相当。

Abstract:

Flow oscillations in a hypersonic inlet caused by interactions between the shock train and separation bubble on inlet shoulder were investigated in a shock tunnel with a freestream Mach number of 6. Synchronized high speed schlieren photography and dynamic pressure measurements were conducted in the inlets with and without a boundary-layer-suction device to better understand the interactions between the shock train and the separation bubble on the shoulder. The results show that the inlet even with the boundary-layer-suction device generates a large scale separation bubble on the shoulder as the shock train moves forward. As a result， coupled oscillations occur in both inlets with and without the boundary-layer-suction device， leading to severe fluctuating pressure. As driven by the shock train， the separation bubble can freely cross the convex corner of the shoulder to manifest its nature of low frequency oscillations. The pressure fluctuation in the shock train dramatically changes the shape of the separation bubble. In turn， the variation of the separation bubble affects the pressure in the shock train. Thus， the low frequency coupled oscillations can be maintained. The same low frequency oscillation characteristics were observed in the inlet without the boundary-layer-suction device. However， the shock train oscillations show a certain broadband features in the inlet with the boundary-layer-suction device， which are different from the low frequency oscillations of the separation bubble， because the suction slots impede the communion between upstream and downstream. When the low frequencies of the coupled oscillations in both inlets are nondimensionalized by the oscillation range of the separation shock and the velocity at the inlet entrance， the Strouhal numbers St range from 0.011 to 0.021， which are similar to the low frequency oscillations of a canonical separation bubble.