预测非平衡稀薄流动中壁面剪切和传热的模型理论及其应用

Detailed design of the thermal protection system has been increasingly emphasized in development of the new generation near-space hypersonic cruise vehicles. Generally, sharp leading edges are used to reduce the pressure drag acting on these vehicles. While the total drag is surely greatly decreased, the viscous friction drag, in contrast, has been significantly increased, and the aeroheating environment becomes very severe. Most of the previous studies are interested only in the total drag and the aeroheating performance near the stagnation point. In order to precisely predict the flight stability and the total heat input, it is very necessary currently to concern distributions of the skin friction and the heat flux along the vehicle’s body. In classical theories, the skin friction and the heat flux are interrelated by the Reynolds analogy, but in the nonequilibrium rarefied flows, it is still unclear how distributions of the skin friction and the heat flux vary, and whether or not an analogy relation between them still exists. In our previous work, the applicant has studied the rarefied gas effects and nonequilibrium real gas effects on the stagnation point aeroheating performance of sharpened noses, and found an approach to establish analytical theories in this research field. As an extension and promotion, this project will employ the theoretical modeling and the direct simulation Monte Carlo method to study the rarefied gas effects and nonequilibrium real gas effects on surface shear and heat transfer over the typical aerodynamic shapes. The contents of this project have both important academic significance and great application value.

新型近空间高超声速巡航飞行器的研制日益重视对气动热防护体系进行精细化设计。这类飞行器采用尖头薄翼的外形以减小压差阻力，但总阻力降低的同时，摩擦阻力却上升了，同时气动热环境随之恶化。以往研究多关注总阻力和驻点气动加热情况，但要精确预测飞行稳定性和气动加热总量，还需要研究整个机身的摩阻和热流分布情况。经典理论中，摩阻和热流二者是通过Reynolds比拟关系相互关联的，但在非平衡稀薄流动中，摩阻、热流分布的规律是什么样的？二者之间是否还有比拟关系？尚无明确答案。项目申请人在之前项目中已经研究了近空间飞行器前缘驻点及其下游气动加热问题中的稀薄气体效应和非平衡真实气体效应，找到一条在该领域内建立解析理论的道路。本项目是前期研究的推广深化，拟采用模型理论分析手段结合直接模拟蒙特卡洛方法，研究典型气动外形壁面剪切和传热分布受稀薄气体效应和非平衡真实气体效应的影响。该研究同时具有重要的学术意义和应用价值。

新型近空间高超声速巡航飞行器的研制日益重视针对气动热防护的精细化设计。这类飞行器采用尖头薄翼的外形以减小压差阻力，但总阻力降低的同时，摩擦阻力却上升了，同时气动热环境随之恶化。从物理机制上说，驻点附近以强压缩流动为主，机身附近流动及传热则具有强剪切主导或强压缩与强剪切耦合作用的特征，且热化学非平衡效应比较显著。本项目采用模型理论分析手段，结合直接模拟蒙特卡洛方法，研究了非平衡真实气体效应对典型气动外形气动力/热特征的影响。研究发现，在高超声速平板流动、Couette流动和钝体驻点下游等典型强剪切流动中，都可以根据各物理化学过程的时间特征尺度，定义具有真实物理意义的非平衡流动判据，并基于这些无量纲判据构建气动力/热的理论预测公式。这些非平衡判据的定义形式和有效性表明，在考虑热化学非平衡效应影响时，各具体强剪切流动模型之间有一定相似性，因而可以在统一的框架下分析讨论。另外也发现，强剪切和强压缩边界层传热机制具有相似性，项目负责人前期在强压缩流动研究中已建立一些广义模型理论，可基于该相似性推广应用于强剪切流动与传热问题的研究。本项目给出了典型非平衡流动中气动加热的快速评估和简化计算方法，具有重要的学术意义和潜在的应用价值。依托该项目发表的文章已被多次引用和积极评价，部分研究成果也在工程单位得到应用。该项目研究也为我们后续关于强剪切-强压缩耦合作用的研究开启了新思路。