Description: Control and management of cryogenic propellant tank pressures in low gravity is an important technical challenge to overcome for future long duration space missions. Advanced techniques such as thermodynamic vent systems (TVS) are currently being designed for low-gravity space systems, and advanced computational tools are required to analyze the complex multi-phase physics involved. The proposed effort extends computational fluid dynamics capabilities to consider the behavior and effects of turbulence on heat/mass transfer at the tank gas/liquid interface and dispersed-phase droplet vaporization. Model extensions to fundamental kinetics-based mass transfer models are investigated for application to cryogenic systems. The methodology will be tested with the CRUNCH CFD code which incorporates real-fluid equations-of-state for cryogenic fluid mixtures with rigorous fluid property definitions, and an advanced dispersed phase spray model that permits non-equilibrium mass, drag, and heat transfer with the surrounding continuum fluid. The models improvements will be readily transferable to alternate codes and support unsteady RANS simulations in an Eulerian-based gas/liquid framework. This technology will support cryogenic system analysis for long duration space exploration activities.

Benefits: The end-product will be high-fidelity, computational models that would be used in advanced Computational Fluid Dynamics software to support design/analysis of cryogenic propellant management methods in both upper-stage and space exploration systems. This innovation addresses core needs of NASA�s longer term vision for the mission to Mars and other space exploration activities that are of long duration. The more advanced and efficient cryogenic propellant management techniques being developed such as thermal vent systems (TVS) are governed by non-equilibrium droplet physics and phase change and require the higher fidelity models being developed in this effort.

The commercial market for cryogenic simulation software includes industries dealing with liquefied gases who would be interested in more efficient and cost effective methods for long term storage and transportation of cryogenic liquids; with the immense interest in hydrogen as a green fuel we foresee increased opportunities. It is also relevant to the petroleum industry where liquefied natural gas use is increasing and safety issues with tankers and LNG terminals are important. The broader technology of multi-phase, spray modeling has wide applications as a fundamental technology for a wide array of industries including the chemical process industry, ink-jet printers, and fluidized bed among others. Commercial space ventures ranging from space transportation systems (COTS) for the international space station (ISS), to low-cost satellite launch systems are getting an infusion of venture capital and would provide a market for accurate simulation tools for low gravity propellant storage management.