We report a newly identified aerodynamic cooling mechanism in the onset of hypersonic wall-bounded turbulence. We first experimentally investigated a flared cone with a smooth surface in a Ma 6 wind tunnel using fast-response pressure sensors, Rayleigh scattering flow visualization, and infrared thermography, which confirmed a cooled region (denoted as CS) downstream of a highly heated region (denoted as HS) on the model, as shown by Franko and Lele [J. Fluid Mech. 730, 491–532 (2013)] and Sivasubramanian and Fasel [J. Fluid Mech. 768, 175–218 (2015)]. We then performed calculations based on both linear stability theory and direct numerical simulations to understand this mechanism. We found that the phase difference ϕpθ between the periodic pressure and dilatation waves plays an important role in the interchange between thermal and mechanical energy in a hypersonic wall-bounded flow. Using porous steel to modify the model surface’s sound admittance, we experimentally show that it is possible to modify the cosine value of ϕpθ to be negative near the wall and thus reduce the temperature growth. These results can provide insight into the thermal protection design of future hypersonic vehicles.

中文翻译：

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高超声速湍流开始时的声波诱导冷却

我们报告了一种新发现的高超声速壁面湍流开始时的空气动力学冷却机制。我们首先使用快速响应压力传感器、瑞利散射流可视化和红外热成像对 Ma 6 风洞中具有光滑表面的喇叭形锥体进行了实验研究，这证实了高热区域下游的冷却区域（表示为 CS）。表示为 HS）在模型上，如 Franko 和 Lele [J. 流体机械 730, 491–532 (2013)] 和 Sivasubramanian 和 Fasel [J. 流体机械 768, 175–218 (2015)]。然后，我们根据线性稳定性理论和直接数值模拟进行计算，以了解这种机制。我们发现周期性压力波和膨胀波之间的相位差 ϕpθ 在高超声速壁面流动中的热能和机械能之间的交换中起着重要作用。使用多孔钢来修改模型表面的声导纳，我们通过实验表明可以将 ϕpθ 的余弦值修改为靠近壁面的负值，从而减少温度增长。这些结果可以深入了解未来高超音速飞行器的热保护设计。