CFD validation of k-site tank self-pressurization under varying fill levels and heat fluxes with different turbulence models

Abstract

Accurate prediction of cryogenic tank self-pressurization is critical for NASA’s short- and long-duration missions, where heat leakage into storage systems occurs through insulation, structural supports, and penetrations. To address this need, a two-phase CFD model was developed to simulate the self-pressurization of a cryogenic storage tank partially filled with liquid hydrogen. The model employed the Volume-Of-Fluid (VOF) approach to capture two-phase flow behavior, incorporating interfacial heat, mass and momentum transfer between the liquid and vapor phases. Validation was carried out against self-pressurization experiments performed using the K-site flightweight hydrogen storage tank at NASA Glenn Research Center. Initial validation focused on a 49 % liquid fill level followed by extension to additional fill levels of 29 % and 83 %, studied in the experiment. Laminar and turbulent simulations were performed, along with conjugate heat transfer, to evaluate pressurization dynamics across different operating conditions. Numerical results for tank pressures and fluid temperature are compared with experimental data under external tank heat fluxes of 3.5 and 2.0 W/m². The effects of turbulence modeling, liquid fill level, and localized heat leaks through instrumentation penetrations are analyzed and discussed in detail.