发汗冷却液-气相变动态过程机理研究

Hypersonic vehicles experience huge aerodynamic heat when travelling at high speed, resulting extremely high heat flux onto the leading edge that exceeds the performance of current systems and up-to-date material limits. Under the requirement of developing innovative and effective thermal protection system to protect the vehicle’s interior, this project will carry out research on the theoretical model, numerical approach and experimental techniques for the transient process of transpiration cooling with liquid-vapor phase change. In this project, the mathematical model for the transient process of transpiration cooling with phase change under time-varying external heat and force loads is established via an interface-capturing method, and self-compiled algorithm is coherently embedded into commercial software to achieve the accurate simulation and computation. Mechanism and dynamic characteristic experiments are then designed and conducted to verify the mathematical model and numerical approach, to study the fluid flow/ heat transfer/ phase change characteristics of liquid coolant within porous matrix, and to analyze the comprehensive performance and efficiency of transpiration cooling structure. The proposed project is aimed at revealing the dynamic transition of liquid coolant phase change in the porous matrix and the time-varying property of fluid-solid conjugated heat transfer, and finally yielding an optimization scheme of the transpiration cooling structure by which the precise injection of liquid coolant according the spatial and temporal distributions of external thermal and force load could be realized. The research output of the proposed project will be of great significance to the improvement of mechanism investigation on the liquid-vapor phase change transition in microstructure, and lay the foundation for the engineering application of transpiration cooling technique as the thermal protection system on the hypersonic vehicles.

针对承受极高热载荷的新型高超声速飞行器尖化前缘对先进高效主动热防护系统的需求，本项目将开展具有工质相变（液-气）的发汗冷却瞬态问题的理论模型、数值方法及实验技术研究。通过相变界面追踪的方法建立时变气动热/力载荷下相变发汗冷却瞬态过程的数学模型，采用源代码编译与商业计算软件相结合的方式实现数值模拟，并进行液态冷却工质在多孔骨架内的流动/传热/相变机理实验和前缘结构发汗冷却特性实验，对瞬态形式的数学模型和数值方法验证并分析结构综合冷却效果，以期揭示多孔结构内液态工质相态演变规律和随时间变化的流-固耦合传热机制，提出冷却工质高精度（定位/定量/定时）注射的发汗冷却结构的优化方案。项目研究成果将对微结构内液-气相态演变机制的阐明和完善有重要意义，为液体相变发汗冷却技术在高超声速飞行器热防护系统上的工程化应用奠定基础。

发汗冷却作为一种效率极高的新型主动冷却技术，有望突破临近空间飞行器高热部位的热防护瓶颈，然而其所涉及的多孔结构内液体相变过程热力耦合特性非常复杂，给结构设计和主动控制带来难题。本项目围绕具有液-气相变的发汗冷却的瞬态问题开展了一系列基础理论和实验研究，主要包括：1）对公开研究中的多种数学模型和边界条件的准确性和普适性进行了鉴别，对剧烈液-气相变导致的流固耦合传热非平衡现象进行了定量分析；2）建立了瞬态形式的半混合模型，自编程序对多种时变热载荷下发汗冷却瞬时响应进行了预测，分析并比较了两种冷却剂注入方式（定压和定量）下发汗冷却系统的稳定性，发现了特有的瞬态传热恶化和气堵现象；3）开展了液态水在多孔骨架内相变传热实验研究，发现了系统热响应延迟效应和在特定条件下的非稳定波动新现象，提出了两个解决途径——对液态水改性和固化，创新性研发了丙二醇改性水溶液和固态水凝胶发汗冷却，提出的新冷却机制和概念存在广阔的研究和应用前景；4）通过源代码编译嵌入商业计算软件，实现了外部气动环境-复杂发汗冷却结构的耦合建模和数值模拟，揭示了液态冷却工质从储存腔到飞行器表面的相态演变和输运特性，评估了外部气动环境对结构综合冷却性能的影响，发现并量化表征了液态工质吸热相变引起的非线性渗流力学特性；5）根据外界热/力载荷的时空分布设计了一系列发汗冷却优化方案，如解决前缘驻点冷却不足的气膜-发汗双层壁结构和凹腔-发汗复合结构、及针对激波干扰局部高热区的梯度孔隙率和冷却剂分腔设计，明确了液体相变发汗冷却作为极高热流密度下轻质热防护结构的工程应用价值和可行性。项目迄今发表论文19篇，其中SCI论文10篇、EI论文7篇；授权发明专利1项；培养毕业博士生1人、硕士生2人。