Analyses of Cryogenic Propellant Tank Pressurization based upon Experiments and Numerical Simulations
The active-pressurization of cryogenic propellant tanks for the launcher application was analyzed in this study. Therefore, ground experiments, numerical simulations and analytical studies were performed with the following important results: In order to minimize the required pressurant gas mass, a higher pressurant gas temperature is advantageous or the application of helium as pressurant gas. Numerical simulations of the pressurant gas mass using Flow-3D show good agreement to the experimental results. The dominating heat transfer during pressurization appears from the injected pressurant gas to the axial tank walls and the predominant way of phase change during the active-pressurization phase depends on the type of the pressurant gas. After the end of the pressurization phase, a significant pressure drop occurs. A theoretical model is presented for the analytical determination of this pressure drop.
Experimental and Numerical Investigation of Stratification and Self pressurization in a High Pressure Liquid Nitrogen Storage Tank
ABSTRACT This paper discusses the evolution of stratification and self-pressurization in a cryogenic storage tank. The heat ingress due to the large temperature difference between ambient and cryogen leads to thermal stratification and self-pressurization. The prediction of the thermodynamic state of cryogen is required for the successful execution of any space mission. An experimental cryogenic test tank which is a combination of an evacuated vacuum jacket and multilayered insulation has been designed, fabricated and is used for stratification studies using liquid nitrogen as the model propellant. Stratification at two conditions were tested; ‘venting’ and ‘non-venting’. During venting condition, only saturated boiling occurs, and the degree of thermal stratification is very less. Whereas during non-venting condition, there is a significant amount of thermal stratification and the degree of thermal stratification increases with working pressure. For a deeper understanding of the phenomenon and better prediction of the state of cryogen, a numerical model had been developed and validated with the experimental result. A stratification parameter has been used to quantify the degree of stratification for both “venting” and “non-venting” conditions. The model developed can be used for accurate prediction of the state of cryogen.
Resonant three-dimensional nonlinear sloshing in a square-base basin
An asymptotic modal system is derived for modelling nonlinear sloshing in a rectangular tank with similar width and breadth. The system couples nonlinearly nine modal functions describing the time evolution of the natural modes. Two primary modes are assumed to be dominant. The system is equivalent to the model by Faltinsen et al. (2000) for the two-dimensional case. It is validated for resonant sloshing in a square-base basin. Emphasis is on finite fluid depth but the behaviour with decreasing depth to intermediate depths is also discussed. The tank is forced in surge/sway/roll/pitch with frequency close to the lowest degenerate natural frequency. The theoretical part concentrates on periodic solutions of the modal system (steady-state wave motions) for longitudinal (along the walls) and diagonal (in the vertical diagonal plane) excitations. Three types of solutions are established for each case: (i) ‘planar’/‘diagonal’ resonant standing waves for longitudinal/diagonal forcing, (ii) ‘swirling’ waves moving along tank walls clockwise or counterclockwise and (iii) ‘square’-like resonant standing wave coupling in-phase oscillations of both the lowest modes. The frequency domains for stable and unstable waves (i)–(iii), the contribution of higher modes and the influence of decreasing fluid depth are studied in detail. The zones where either unstable steady regimes exist or there are two or more stable periodic solutions with similar amplitudes are found. New experimental results are presented and show generally good agreement with theoretical data on effective domains of steady-state sloshing. Three-dimensional sloshing regimes demonstrate a significant contribution of higher modes in steady-state and transient flows.