针栓式喷注单元膜束撞击雾化混合过程数值模拟

为了全面认识针栓式喷注器喷雾场结构，基于自适应网格加密技术和分三相计算的PLIC VOF（Piecewise Linear Interface Calculation Volume of Fluid）方法对针栓式喷注单元膜束撞击雾化混合过程进行了仿真分析，通过对两路推进剂分别进行界面追踪，获得了膜束撞击雾化混合过程的详细结构特征，与高速摄影试验结果定性定量对比均吻合较好，验证了数值方法的准确性。以此为基础对膜束撞击的喷雾场结构、撞击变形过程、流场涡结构、雾化破碎典型特征及破碎后的雾化混合分布特征进行了识别分析，结果表明：膜束撞击形成了液束未穿透液膜和液束穿透液膜2种不同的喷雾扇结构。膜束撞击形成的喷雾扇呈"Ω"形，膜束同时发生弯曲变形和横截面变形。另外，膜束撞击同时受到正压和剪切应力作用，导致了一系列复杂涡流现象，使得相互作用增强，雾化混合均增强，这也是膜束撞击喷注构型优于膜膜撞击的本质原因。最后，还发现膜束撞击喷雾场液滴分布呈现分区结构特征，分别是液束控制主导的上雾化区、液膜控制主导的下雾化区及夹在中间的混合区，实际中应兼顾雾化特性和混合特性，选取中等动量比膜束撞击，这可为针栓式喷注器的理论研究和工程设计提供重要参考。

Numerical simulation of spray and mixing process of impingement between sheet and jet in pintle injector element

To fully understand the spray field structure of pintle injectors, this study simulate and analyze the spray and mixing process of impingement between a liquid sheet and a liquid jet in a pintle injector element, based on the adaptive mesh refinement technology and PLIC VOF (Piecewise Linear Interface Calculation Volume of Fluid) method in which three phases are separately calculated. The detailed structural characteristics are obtained in the impinging and atomizing mixing process by tracking the phase interfaces of the two propellants respectively. These characteristics are compared qualitatively and quantitatively with the results of the high-speed photography test, showing good agreement, and verifying the accuracy of the numerical method. Furthermore, the spray field structure, the impact deformation process, the vortex structure, the typical characteristics of spray and breakup, and the distribution characteristics of spray and mixing are identified and analyzed. Results show that two different spray fan structures are formed, namely, the jet not penetrating the liquid sheet and the jet penetrating the liquid sheet. The spray fan formed by the impingement is in the shape of "Ω", with the bending deformation and the cross-sectional deformation occurring simultaneously for both the liquid sheet and liquid jet. In addition, the impingement is simultaneously subjected to positive pressure and shear stress, resulting in a series of complex vortex phenomena, and consequently enhancing the interaction and the spray and mixing process. This is also the essential reason why the injection configuration of the impingement between a sheet and a jet is superior to that between two sheets. Finally, it is also discovered that the droplet distribution in the spray field is characterized by the regional structures, namely, the upper spray zone dominated by the liquid jet, the lower spray zone dominated by the liquid sheet, and the mixing zone sandwiched in between. The spray characteristics and mixing characteristics should be considered comprehensively in practice, and the middle momentum ratio should be selected to provide important reference for theoretical research and engineering design of pintle injectors.