微重力下低温贮箱内气液两相流界面特征与增压规律研究

Long term on-orbit security storage of cryogenic propellant is necessary for deep space exploration. The characteristics of gas-liquid two-phase flow in microgravity are quite different from that on earth. Under the effect of space radiation heat flux, cryogenic fluids will experience the processes of temperature rise and liquid vaporization, and then bring about a continuous pressure rise. Understanding the interfacial configuration and pressurization behaviors of on-orbit cryogenic fluid is beneficial to the tank structure design as well as the selection of pressure control approaches, while the correlation researches in our country is still at its initial stage. In this research project, theoretical analysis, numerical simulation, and experimental approach will be applied to study the two-phase flow and pressurization behaviors for cryogenic tank in microgravity. The numerical approach will be employed to analyze the influence of microgravity on gas-liquid interfacial configuration, and the formation mechanism of two-phase flow will also be explored. A new phase change model, which can account for the vapor-liquid heat and mass transfer effects in microgravity, will be constructed. Moreover, several CFD models will be built to study the tank pressurization behaviors and boil-off rate at different on-orbit operating conditions and a list of approaches will be attempted to reduce the time consumption of CFD computations. In addition, a test platform will be established to study the thermal distribution and tank pressurization rate in several operating conditions, including self-pressurization, helium pressurization, and fluid mixture by ejector. Based on the above researches, a selection principle of pressure control approaches, which aims at different on-orbit storage target of cryogenic propellant, will be provided. The works of this project will narrow the gap between our country and advanced countries in the field of on-orbit cryogenic fluid management, and the results will provide a theoretical and technical guideline for domestic human lunar project and other deep space explorations.

深空探测要求低温推进剂能够实现长期在轨安全贮存。微重力下的气液两相流表现出不同于地面的特征。在空间热作用下，低温流体升温气化，导致贮箱压力持续升高。准确预测低温流体在轨时的界面形态与压力变化可以为贮箱结构设计与控压技术选用提供依据，而我国在该领域的研究尚处于起步阶段。本项目拟采用理论分析、数值模拟与地面实验相结合的手段就处于微重力下的低温贮箱内部两相流运动与增压规律开展研究。采用数值方法研究重力缺失对气液两相流界面分布的影响，探明两相流运动的形成机理；建立微重力气液热质传递模型；构建CFD模型预示贮箱压增过程，探究提高CFD计算经济性的途径；搭建实验平台研究贮箱自增压、氦气增压、喷射器混合工况下的温度场分布与压力变化规律；针对不同的贮存目标提出压力控制技术选用原则。本项目的研究可缩小我国在低温流体在轨安全管理领域与国际先进水平的差距，为我国载人登月及深空探测提供理论和技术支持。

低温推进剂具有高比冲、大推力、无毒无污染等优点，在航天地面发射与深空探测中扮演重要角色。低温液氢、液氧已被我国选为开展载人月球探测的首选燃料。低温推进剂的空间应用必须解决低温燃料空间蒸发损失及相关的流体管理技术难题。本项目以低温推进剂空间管理的相关热力学问题为对象，通过理论分析、计算仿真，地面实验相结合的手段就处于微重力下的低温贮箱内部两相流与增压规律开展研究。针对液氢池沸腾换热，构建了可预测其在整个沸腾区的换热模型，采用该模型，可实现液氢沸腾换热的精确求解。结果表明：液氢在ONB、CHF、MHF三个临界点的壁面过热度分别为0.1K、3K、4K；对应的热流分别为10 W/m2、105 W/m2 、103 W/m2。揭示了重力因素对核态沸腾、膜态沸腾换热强度的内在影响，并构建了相应的预测模型。采用该模型，在已知液氢地面常重力沸腾换热的基础上，可预测任一重力下的换热强度。构建了可预测低温贮箱纯质系统、多组分系统内气液热质传递的相变模型，实现了低温流体相变问题的数值求解。采用CFD技术仿真了低温贮箱在微重力下场分布规律，结果发现，微重力下气液相态分布呈现出不同于地面工况的特征。当重力降至10-3g时，可见明显的气液界面变形，当重力降至10-6g时，液相将气相完全包裹。构建了两种CFD模型研究低温贮箱在轨贮存期间的增压规律，基于VOF界面捕捉技术的CFD模型将流体综合考虑，能够将界面形态与场变化耦合求解，但计算经济性较差。基于集总参数气枕的模型仅针对液相区建模求解，涉及气枕压力、气枕与液相热质传递作用均通过UDF植入考虑，该方法计算经济性较高。针对热力学排气系统(TVS)的控压特性，以R123为实验工质搭建了地面原理性实验平台，并开展了实验研究，揭示了TVS的工作可行性与工作规律。本项目工作对于正在开展的航天低温具有一定的支撑，对于我国掌握低温推进剂的空间应用、开展下一阶段成熟度更高的研究提供参考。