针对高空航天飞机等再入飞行器表面缺陷或防热瓦缝隙导致的局部压力过高和气动加热问题，采用直接模拟Monte Carlo （DSMC）方法研究了飞行高度为80 km的稀薄流区高超声速凹腔绕流问题，考虑气固相互作用（GSI）模型对凹腔流场特征和表面压力、热流的影响。结果表明：稀薄流条件（80 km）下，GSI为完全漫反射时，在凹腔前缘分离的剪切层再次附着在后缘，在凹腔内部形成一个充满腔体的单涡结构；随着GSI从完全漫反射向镜面反射变化，气体与凹腔表面之间的切向动量交换减弱，即黏性剪切作用减弱，外部气流被卷入凹腔的程度减弱，导致涡结构不断减小直至消失，凹腔底部逐渐出现所谓的"死水区"。与完全漫反射相比，镜面反射或近镜面反射会导致凹腔上游侧面的峰值压力和峰值热流以及下游侧面的峰值压力剧烈增大，在飞行器设计中，应特别留意上述表面的压力载荷和热载荷。
To alleviate the high local pressure and heat loads caused by cavities or imperfections on hypersonic vehicle surfaces, we investigate rarefied hypersonic flows over cavities at an altitude of 80 km using the Direct Simulation Monte Carlo (DSMC), examining the effects of Gas-Surface Interaction (GSI) models on flow characteristics inside the cavity, surface pressure and heat flux over the cavity surfaces. Results show that, in the rarefied regime (80 km), one primary vortex is formed as a result of shear layer separation and reattachment. In addition, as the GSI changes from perfect diffuse reflections to pure specular reflections, the exchanges of momentum in the tangent direction between the incident gas molecules and the cavity surfaces weaken, i.e. the viscous shear effects are weakened, lessening the ability of the external gas to penetrate deeper into the cavity. Therefore, the vortex inside the cavity progressively diminishes till ultimately disappears, leaving behind a so-called "dead-water region" at the bottom of the cavity. In comparison with the perfect-diffuse case, pure or near specular reflection causes a significant increase in the peak pressure and heat flux on the front wall of the cavity, and the peak pressure on the aft wall. Therefore, much attention should be paid to the pressure and heat loads on the aforementioned surfaces in the aerodynamic design.
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