液体火箭贮箱增压排液过程三种气枕模型的数值对比

Numerical comparison of three ullage models for the tank pressurization process of liquid rocket during outflow

针对液氧贮箱氦气增压排液过程,分别建立了零维整体模型、一维分层模型及二维计算流体力学(CFD)模型对气枕物理场的变化规律进行数值研究.零维及一维模型采用经验公式求解气枕与壁面间的换热量,而二维CFD模型通过低雷诺数k-ε模型确定流体与固壁间的耦合换热作用.计算时氦气采用理想气体模型.利用三种模型分别预测了贮箱内气枕压力、气枕平均温度及温度分布规律.计算结果表明:三组结果分布合理,不同模型的结果之间能够互相印证;对于气枕及与气枕接触壁面沿轴向的温度分布,在气枕主体区一维模型与二维模型预测结果基本吻合,而在靠近消能器的气枕上端,两种模型预测值存在偏差;当增压气体入口速度较大时,气枕上端径向温度分层明显,需采用二维CFD模型才能展示气枕物理场分布.

In view of the process of helium pressurization in a liquid oxygen tank during outflow,the numerical methods of zero-dimensional integrated model,one-dimensional stratification model and two-dimensional computational fluid dynamics（CFD） model were adopted to study the variation law of ullage physical field,respectively.An empirical formula was set up to solve the heat transfer rate between ullage and tank wall in the zero-dimensional model and in the one-dimension model,while the low Reynolds number k-ε model was selected to calculate the coupled heat transfer rate between fluid and tank wall in the two-dimensional CFD model.The helium density was calculated by the ideal-gas model.The ullage pressure,ullage average temperature and temperature distribution were forecasted by these three models,respectively.The computational results show that the forecasted ullage pressure and ullage average temperature of three models show reasonable distribution,and the results of different models can be confirmed one another.In addition,the calculated axial temperature distribution in the ullage gas and in the ullage wall of the one-dimensional model is close to that of two-dimensional model in the main region,while the forecasted temperature distribution inside the ullage top nearby gas injector obviously deviates in different models.Moreover,the higher inlet velocity of the pressurized gas means more obvious radial temperature distribution inside tank top.Thus the two-dimensional CFD model should be selected to present the physical field distribution in the ullage when the inlet velocity is high.