Numerical investigation of the operating process of the liquid hydrogen tank under gaseous hydrogen pressurization

In order to accurately predict the whole operating process of a liquid hydrogen tank under gaseous hydrogen pressurization, a 2-D axial symmetry Volume-of-Fluid (VOF) based numerical simulation method is established. Phase change and turbulence models are included in the numerical simulation. The variations of physical parameters such as the ullage mass, temperature and pressure, are carefully analyzed. The different effects are given based on simulations with and without phase change, and the comparison between feedback pressurization and open pressurization is also given. Compared with the NASA's experiment under the feedback pressurization, the simulation results show that the deviation of pressurant gas masses consumption is 11.0% during the whole operating process. The deviation of the total ullage mass is -0.8%, 1.4% and 7.6% for the ramp period, the hold period and the expulsion period, respectively. The deviation of phase change mass is 7.5% and -21.5% for the ramp period and the expulsion period, respectively. The simulation results also reach an agreement with the experiment on the energy absorption proportions and demonstrate that most of the energy addition from the external environment and the pressurizing gas is absorbed by the tank wall. The liquid gains the least energy during the expulsion period. Temperature stratification appears along the axial direction in the surface liquid region and the ullage region, and the bulk liquid is in a subcooled state. The location of phase change mainly appears near the vapor-liquid interface, where the net condensation appears during the ramp period and the hold period, while the net vaporization appears during the expulsion period. The phase change increases the amplitude of temperature oscillation. The open pressurization has an ullage pressure peak and an average ullage temperature peak, which lead to large impacts on the tank structure, but the control of the inlet mass flow rate is easy to implement. The feedback pressurization could maintain a steady ullage pressure, but more pressurant gas masses are consumed, and the control of inlet mass flow rate becomes more complicated. The simulation results can be used as references for design optimization of the pressurization systems of cryogenic liquid launch vehicles in order to save pressurant gas masses and decrease the ullage pressure peak which could reduce the tank wall thickness and enhance the carrying capacity of liquid launch vehicles. (C) 2019 Elsevier Masson SAS. All rights reserved.