Validation of a Stratified Ullage Nodal Model Simulating Cryogenic Tank Pressurization

Cryogenic propulsion system design requires accurate prediction of pressurant mass required to achieve and maintain propellant tank pressure. An axially stratified ullage model developed using the Generalized Fluid System Simulation Program was validated by comparison of analysis results to experimental measurements of cryogenic tank pressurization. Analysis and test data are compared for a 1.52-meter diameter spherical aluminum tank filled with liquid hydrogen, pressurized with gaseous hydrogen or helium, and drained while maintaining constant pressure. The scope of this validation activity includes assessment of initial tank pressurization, re-pressurization hold, and pressurized liquid drain. Test results selected for analysis model validation consist of local, axial tank wall and ullage gas temperature profiles measured at the end of liquid drain. Additional test-derived results used for validation were obtained at the end of initial tank pressurization, the end of re-pressurization hold, and the end of pressurized liquid drain and consist of pressurant and ullage gas mass and energy, which were calculated from measured flow rate, temperature, and pressure. Operational parameters were varied to define sensitivity of results to tank wall thickness, pressurant injector geometry, pressurant inlet temperature, initial pressurization rate, re-pressurization hold duration, and pressurized drain rate.