Validation of Multi-species Two-phase Turbulent Flow CFD Model for Cryogenic Tank Pressurization

Effective management of cryogenic propellants is a critical technology for NASA's deep space exploration goals. Consequently, predictive modeling of cryogenic fluid management (CFM) operations, such as propellant transfer (tank filling and draining), tank pressure control (pressurization and depressurization), and slosh induced ullage collapse is of key interest. A computational fluid dynamics (CFD) model capable of predicting key physics for one such CFM operations, cryogenic propellant tank pressurization with condensable and non-condensable pressurant, is developed in the Loci-Stream solver and validated. Simulation of CFM operations requires modeling of multiple physics and scales. The physics includes multiphase turbulent flow, species transport, gas-liquid and fluid-solid heat transfer, and interphase mass transfer and associated latent heat transfer. To achieve practical simulation wall times, Reynolds-average Navier Stokes (RANS) or hybrid RANS-LES (Large Eddy Simulation) models are used for turbulence modeling. Microscale interface dynamics of interphase turbulence transport and phase change are upscaled to mesoscales for practical engineering applications. An asymmetric gas-liquid interface turbulence damping approach is used based on direct numerical simulation (DNS), experimental evidence and previously validated RANS CFD model. The gas side of the interface is treated akin to a wall for interface turbulence modeling purpose, however no special turbulence treatment is enforced on the liquid side of the interface. A kinetic theory based phase change model predicts evaporation and condensation based on the temperatures and pressures of the gas and liquid near the interface, as well as the interface saturation condition. Validations using multiple autogenous and helium ground pressurizations of a cryogenic tank conducted at University of Bremen are presented to demonstrate the effectiveness of the modeling techniques.