发汗冷却中的压力-速度耦合
Pressure-Velocity Coupling in Transpiration Cooling
AI总结：
本文结合孔隙网络模拟、直接数值模拟与CNN耦合函数，研究发汗冷却中压力驱动渗流与高温湍流边界层的相互作用及其对冷却效率、TKE和压力脉动谱的影响。
摘要：
发汗冷却是一种在航空航天应用中日益受到关注的主动热防护系统，其中冷却剂通过多孔壁渗出并进入高温外部流动。本研究聚焦于高温湍流边界层与穿过多孔壁的压力驱动冷却剂流动之间的相互作用。研究通过孔隙网络模拟获得了用于表征多孔介质内流动特征的耦合函数，随后将这些函数与大冷却平板上湍流边界层的直接数值模拟相耦合。研究采用了两类不同的耦合函数：不考虑相邻孔隙之间流动相互作用的线性表达式，以及纳入空间相关性的浅层卷积神经网络（CNN）。所有耦合算例均表明，由于冷却剂注入开始所伴随的平均压力沿流向变化，吹除作用呈现显著变化。这一趋势也反映在冷却效率上；在CNN耦合算例中，由于纳入了相邻孔隙之间的横向流动，该趋势得到缓解。由于近壁湍流衰减与吹除比增加导致的剪切增强之间存在竞争效应，耦合还改变了各耦合算例中的湍动能（TKE）分布。最后，研究表明耦合会影响发汗区域内壁面压力脉动的功率谱密度：其会衰减最大尺度的湍流，同时使较小尺度相对不受影响。
英文摘要：
Transpiration cooling is an active thermal protection system of increasing interest in aerospace applications wherein a coolant is effused through a porous wall into a hot external flow. The present work focuses on the interaction between the high-temperature turbulent boundary layer and the pressure-driven coolant flow through the porous wall. Coupling functions were obtained from pore-network simulations to characterize the flow through the porous medium. These were then coupled to direct numerical simulations of a turbulent boundary layer over a massively-cooled flat plate. Two different types of coupling function were used: linear expressions, which do not account for flow interactions between neighbouring pores, and shallow convolutional neural networks (CNN) which incorporate spatial correlations. All coupled cases demonstrated a significant variation in blowing due to the streamwise variation in mean pressure associated with the onset of coolant injection. This trend was reflected in the cooling effectiveness, and was mitigated in the CNN-coupled cases due to the incorporation of lateral flow between neighbouring pores. The distribution of turbulent kinetic energy (TKE) in the coupled cases was also modified by the coupling due to the competing effects of near-wall turbulence attenuation and increased shear due to increasing blowing ratio. Finally, the coupling was shown to impact the power spectral density of the pressure fluctuations at the wall within the transpiration region, attenuating the largest scales of the turbulence whilst leaving the smaller scales relatively unaffected.
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