液氢缩比贮箱蒸发特性数值模拟及实验验证

Numerical simulation and experimental validation of evaporation characteristics of scaled liquid hydrogen tank

地面缩比贮箱用来模拟箭载液氢贮箱热物理过程及运行特性,包括筒段和壳段,壳段用于支撑筒段。筒段和部分壳段使用泡沫绝热,壳段结构部分裸露在环境中,成为液氢贮箱的主要漏热源。基于计算流体力学方法数值研究了液氢缩比贮箱蒸发特性,构建了基于VOF两相流模型以及Level-set界面跟踪方法的贮箱两相氢流动和相变传热传质数学框架,其中气液界面传质率基于Lee模型计算。框架中的系数、边界条件等作如下考虑:Lee模型中的液化/蒸发系数通过与实验数据对比获得;通过理论分析低温面有/无泡沫保温层的结冰特性,对暴露在环境的泡沫和铝壳表面施加对流换热或常热流边界条件;当贮箱压力达到约2个大气压(0.2 MPa)时,安全阀打开放气保持内部压力不变,基于自定义函数方法模拟阀门开闭实现控制贮箱压力的目的。与实验测量的液位下降速率和气相温度非稳态变化对比表明,构建的数值模型能够较好地模拟液氢贮箱自增压过程的复杂流动、相变传热传质特性。为模拟真实箭载液氢贮箱停放阶段的热物理过程打下基础。

The ground-scale reduction tank is used to simulate the thermophysical process and operating characteristics of the arrow-loaded hydrogen tank, including the barrel section and the shell section which is used to support the barrel section. The barrel section and part of the shell section are insulated by foam, and the shell section structure is exposed in the environment, which becomes the main heat leakage source of the liquid hydrogen tank. Based on the computational fluid dynamics method, the evaporation characteristics of the liquid hydrogen scaled tank were numerically studied. The mathematical framework of two-phase hydrogen flow and phase change heat and mass transfer was constructed based on VOF two-phase flow model and Level-set interface tracking method. The mass transfer rate of the liquid interface is calculated based on the Lee model. The liquefaction / evaporation coefficient in the Lee model was obtained by comparison with the experimental results. By theoretical analysis of the icing characteristics of the low temperature surface with or without foam insulation, convective heat transfer or constant heat flux boundary conditions were applied to the exposed foam and aluminum shell surfaces respectively. When the tank pressure reached about 2 atm (0.2 MPa, absolute), the safety valve was opened and deflated to keep the internal pressure constant. This paper simulates the valve opening and closing based on the custom function method to achieve the purpose of controlling the tank pressure. Compared with the experimentally measured liquid level decline rate and unsteady gas phase temperature change, the constructed numerical model can well simulate the complex flow and phase change heat and mass transfer characteristics of the self-pressurization process in the liquid hydrogen tank, which contributed to the foundation for simulating the thermophysical process during the launch process of the real rocket-loaded liquid hydrogen tank.