极端条件两相界面流与反应流机理、模型与算法研究进展

清华大学喷雾燃烧与推进实验室长期专注于极高速、强可压和高瞬变等极端条件下的两相流和反应流前沿科学问题，并致力于应用基础研究成果解决航空航天动力与推进系统的关键技术难题。综述了实验室近些年在极端条件下两相流动和含化学反应流动物理机理、数理模型与数值算法等方面的研究进展。首先，介绍了实验室发展的耦合高瞬变相变过程的强可压缩气液两相界面流的数理模型和高精度数值方法，以及针对激波受气液（曲）界面约束情况下，描述非定常激波透射/反射（如波角、波强等物理量关系）的激波动力学分析方法。其次，基于上述模型、算法与分析方法，实验室研究了激波液滴相互作用、高速液滴撞击壁面等一系列问题，解析了上述高瞬变过程中复杂波系与界面的时空演化过程。以被激波或壁面冲击的液滴内流体空化初生为例，揭示了曲界面汇聚膨胀波诱导流体空化的机理，推导了预测空化初生位置的理论公式。最后，介绍了面向发动机燃烧室内的强可压缩两相喷雾反应流动，实验室开发了基于Euler-Lagrange框架的高性能数值仿真软件TURFsim，并成功用于真实复杂几何结构的航空发动机燃烧室和超声速燃烧室的数值模拟。以典型的超声速混合层流动数值模拟为例，总结了斜激波增强混合层混合特性的规律及其物理机理，获得了极限条件火核生成及火焰的传播模式与机理，详细分析了液雾弥散与蒸发、小激波和局部爆震波的时空演化特性，提出使用"第三Damk?hler数Da_Ⅲ"定量表征燃烧模式，应用该无量纲参数成功进行了局部准等容燃烧过程的辨识与演化分析。上述研究结果对于航空航天发动机燃烧室复杂物理过程的理解及工程设计具有重要价值。 

Recent Research Progress on the Mechanism,Modelling, and Algorithm of Two-phase Interfacial Flow and Reacting Flow under Extreme Conditions

The Spray Combustion and Propulsion (SCP) Laboratory, which is affiliated with Tsinghua University, is dedicated to the cutting-edge research of two-phase flow and chemically reactive flow under ultra-speed, strongly compressible, and high transient conditions, and the SCP Laboratory applies fundamental research conclusions to solve key technique issues in aerospace power and propulsion area. Recent research progress of SCP Laboratory on fluid mechanism, modelling, and algorithm of two-phase interfacial flow and chemically reactive flow under extreme conditions was summarized. At first, the analytical model and high-precision numerical method of the strongly compressible two-phase interfacial flow with a high transient phase transition process were introduced. Then the unsteady shock wave propagation theory for the relationship of wave angle, wave intensity, and other physical quantities during the shock wave transmission and reflection processes with constraints of the two-phase planar/curved interface was introduced. Based on above model and method, a series of basic flow problems such as shock wave/droplet, high speed droplet/wall collision were studied, and the spatiotemporal evolutions of complex wave and interface system in high transient process were analysed. Taking the cavitation in the shocked droplet as an example, the mechanism of cavitation induced by convergent expansion waves at the curved interface was revealed and the theoretical formula was put forward to predict location of the cavitation core. Furthermore, the strongly compressible two-phase spray reactive flow in combustion chambers was introduced. The SCP Laboratory develops high performance numerical simulation software TURFsim, which is based on the Euler-Lagrange framework, and this software has been successfully applied in the simulation of aeroengine and supersonic combustion chamber with complex geometry. Taking a typical supersonic mixing layer simulation as an example, the physical mechanism of the oblique shock wave enhanced mixing was summarized. The propagation mode and mechanism of fire nuclei and flame propagation under extreme conditions were put forward. The spatiotemporal evolutions of sprays, wavelets, and local detonation waves were demonstrated. A quantitative combustion characterization method with the third Damk?hler number Da_Ⅲ was proposed and this nondimensional parameter was applied on the identification and evolution analysis of local quasi-isochoric combustion process. The above research results play an important role on the understanding of complex physical processes and engineering design of aerospace engines.