Research on Interfacial Flow and Thermal Stratification of Cryogenic Liquid Nitrogen in Variable Gravity

In order to study the effects of residual gravitational acceleration g on the flow, phase distribution, temperature distribution, and pressure distribution of liquid nitrogen tank during self-pressurization, the self-pressurization process of liquid nitrogen tank under different g was numerically simulated by the Volume-of-Fluid (VOF) method. The results show that under the condition of large g, the fluid pressure in the tank increases gradually along the direction of residual gravity, and the temperature of the ullage in the tank increases with the continuous heat leakage of the tank wall, and the gas temperature near the wall is the highest, and the gas temperature near the liquid is the lowest, while the temperature in the liquid bulk zone of the tank changes little with time. With the decrease of g, the liquid in the tank is more likely to climb along the wall of the tank with better infiltration, and the temperature difference of the fluid in the tank is gradually reduced. In the case of small g, after the fluid flow in the tank is stable, the ullage will be wrapped in the middle of the tank, forming a spherical bubble. The difference of the fluid temperature in the tank gradually increases and then decreases with time. In zero gravity environment, the presence or absence of heat leakage (q_w = 0.5 W⋅m^–2) on the tank wall has no significant influence on the fluid movement and phase distribution in the tank, and within the initial time interval $\Delta t_{\mathrm{f}} $ (0 ≤ $\Delta t_{\mathrm{f}} $ ≤ 40 s), the influence of the presence or absence of q_w on the temperature distribution of the fluid in the tank also is not significant except near the wall of the tank. Numerical simulation results are expected to provide references to further study the on-orbit pressure control technique of cryogenic liquid tanks and space cryogenic fluid management.