液氮贮箱自增压实验与数值仿真

Experiment and Numerical Simulation of Liquid Nitrogen Tank Self-Pressurization

为研究低温推进剂在常温下的自增压过程,设计了以液氮为模拟介质可视化低温玻璃贮箱自增压实验系统,研究了自增压过程压力和温度的变化规律及体积充填率对压力和温度变化的影响。实验结果表明:气枕区和液体区存在显著的轴向温度分层,液体区温度的上升速率低于压力引起饱和温度的上升速率。压力上升分为有典型意义的三段:初始段、过渡段和稳定段,稳定段的压力上升速率随体积充填率增加而增加。液体区的对流运动在自增压过程受到抑制,气液界面逐渐进入准静止状态。并以实验测得温度作为边界条件,采用流体体积(VOF)模型对整个自增压过程进行了175 s的数值仿真。仿真得到的压力曲线变化规律与实验结果基本一致,稳定段的压力上升速率是实验值的1.58倍。本文得到的自增压物理参数变化规律,为低温推进剂的贮存和贮箱的热防护设计提供参考。

To study the process of the cryogenic propellants during self-pressurization at room temperature, a visual experimental system is designed, which uses the liquid nitrogen as the simulation medium. The change rules of the pressure and temperature as well as the influences of the volume filling rate on the pressure and temperature are analyzed. The experimental results show that the temperature stratification is significant in the gas and liquid regions along the axial direction, and the temperature rising rate in the liquid region is lower than the saturation temperature rising rate which is caused by the gas pressure. The pressure rising curve can be divided into three typical sections： the initial section, the transition section and the stabilization section, and the pressure rising rate in the stabilization section increases with the volume filling rate. While in the liquid region, the convection is suppressed during the self-pressurization, and the vapor- liquid interface is gradually moving into the quasi stationary state. The temperature boundary conditions for the simulation are acquired from the experiment, and the physical process of 175 s during the self-pressurization is simulated by using the volume of fluid （VOF） model. The variation of the pressure curve simulated is essentially in agreement with the experimental resuhs, and the pressure rising rate in the stabilization section is about 1.58 times of the experiment. This paper gives the rule of the tank self-pressurization by the experiment and simulation, which can provide a reference for the cryogenic propellants storage and thermal protection design of tanks.