激波与单液滴相互作用及其对修正质量、动量和热量传递模型的影响

The bulk interests in spray combustion are to study droplets breakup and gasification. However, we now face new challenges to well understand the physical processes and perform mathematical models in supersonic flows, since the mechanism of shock waves interacting with droplets is still unclear. It is significant to study the droplet dynamics considering the interaction of strong shock waves for the development of accurate numerical models as well as the optimization design and performance analysis of scramjet combustor. In the present project, we plan to record the interaction processes of shock waves with single droplets by using high-speed schlieren photography, and improve interface-capturing methods for compressible two-phase fluids with high density ratios. The fine numerical simulations of the droplet/shock wave interaction are performed to present the temporal and spatial evolution of two-phase interfaces. Based on the above results, we will then summarize the laws of droplets dynamics and interface geometry morphology under the action of shock waves, to establish a flow-regime chart for droplet breakup in supersonic flows, which correlates the flow Reynolds number, droplet Weber number, Ohnesorge number and shock wave Mach number. Thus, the rules of droplet/shock wave interaction and the mechanisms of droplet breakup impacted by shock waves will be presented. We will further launch detailed simulations on the high/low speed flows around a single droplet with and without evaporation to investigate the processes of the mass, momentum and heat transfer between the droplet and the surrounding supersonic high temperature fluids. Therefore, considering the compressibility effects resulted from the shock wave action, we will finally obtain the suitable mass, momentum and heat transport mathematical models applied for supersonic flows. The project aims to not only develop accurate numerical prediction methods, but also provide practical models and theory basis for the engineering application of supersonic two-phase flows.

液滴破碎与汽化是喷雾燃烧领域的经典问题，但其在超声速流动极端条件下面临新的挑战，即激波作用下的物理机理尚未清晰，相关模型不完备。研究强激波作用下液滴动力学规律，对于精准数值模型的发展，进而超燃冲压发动机的优化设计与性能分析具有重要意义。本项目将采用高速纹影技术拍摄激波对单液滴的冲击过程，发展大密度比气液两相守恒界面捕捉算法并实现激波与液滴相互作用时空演化过程的精细数值模拟；总结激波作用下液滴动力学和界面形态几何学规律，建立关联雷诺数、韦伯数、欧尼索数及激波马赫数的液滴破碎“流态图”，揭示激波与液滴相互作用规律以及强激波作用液滴的破碎机制；分析单液滴高、低速绕流流场的数值模拟结果，研究激波强可压缩性对液滴与高温高速气流间质量、动量和热量传递规律的影响，修正得到相对完善的超声速流动中液滴“三传”模型及其适用条件，从而为发展准确的数值预测手段及超声速两相流动的工程应用提供实用模型和理论依据。

液滴破碎与汽化是喷雾燃烧领域的经典问题，但其在超声速流动极端条件下面临新的挑战，即激波作用下的物理机理尚未清晰，相关模型不完备。研究强激波作用下液滴动力学规律，对于精准数值模型的发展，进而超燃冲压发动机的优化设计与性能分析具有重要意义。本项目采用高速纹影技术拍摄激波对单液滴的冲击过程，获得了不同激波马赫数条件下的液滴变形、破碎规律。搭建了激波与单液滴相互作用研究实验台，发展了大密度比气液两相守恒界面捕捉算法，建立了强可压两相流动中的高瞬变相变模型及强鲁棒算法，编制了程序和相应的软件。基于自研算法、模型，及其数值计算软件实现了激波与液滴相互作用时空演化过程的精细数值模拟，提取并分析了相互作用过程中复杂波系以及两相界面瞬变特征；总结激波作用下液滴动力学和界面形态几何学规律，揭示激波与液滴相互作用规律以及强激波作用液滴的破碎机制，分析了单液滴在激波作用下流体相变空化的物理特征，强可压缩性对液滴与高温高速气流间质量、动量和热量传递规律的影响，修正得到相对完善的超声速流动中液滴“三传”模型，从而为发展准确的数值预测手段及超声速两相流动的工程应用提供实用模型和理论依据。总之，本项目重要成果与创新包括：1）开发了一套含有相变过程的强可压缩两相界面流动过程的高精度数值模拟算法及软件，2）获得了激波与液滴相互作用过程中复杂波系时空演化结果及物理规律，解释了激波诱发液滴内部空化的物理机制，并系统完整的建立了界面约束的非定常激波解析理论，3）获得了作用液滴之后入射激波的演化规律，液滴受激波冲击后的动力与规律及其主控因素。上述成果对于强可压缩两相界面流动的工程调控具有重要理论价值。