Validation of Multiphase Interface Turbulence Modeling Technique for Cryogenic Fluid Management Applications

Modeling of turbulence transport at a gas-liquid interface has significant impact on phase change and heat transfer at the interface, which directly modulate pressure inside the cryogenic tank – an important quantity of interest for NASA’s deep space flight mission goals. A large range of length scales and time scales encountered in such problems – the interfacial physics has length scale of an order of tens to hundreds of micrometers and time scale of the order of milliseconds or less, but propellant tank length scale is an order of a meter with time scale for operations of interest spanning as long as days – make the modeling very challenging. An elegant interface turbulence modeling strategy was chosen to validate Loci-Stream-VOF – a Computation Fluid Dynamics (CFD) solver used by propulsion fluid dynamics branch at NASA Marshall Space Flight Center (MSFC) – for flight mission predictions. Following the evidence from experiments and direct numerical simulations (DNS), turbulence was damped near the gas-liquid interface in Reynolds Averaged Navier Stokes (RANS) modeling. The gas at orders of magnitude higher density than the liquid, exhibits reduced turbulence transport at the interface, i.e., “wall-like turbulence”. Depending on the flow regime the liquid side turbulence can either be damped (“wall-like”) or undamped or slightly enhanced turbulence (“freestream-like”). This approach was validated by three sets of flight-sized tests performed at NASA with liquid hydrogen, each with unique operations and flow features. Five axial jet driven pressure control tests and six self-pressurization tests conducted at NASA Glenn Research Center using K-site tank along with an unsubmerged autogenous pressurization test conducted at NASA MSFC with Engineering Design Unit (EDU) tank successfully validated this technique. Satisfactory validation using these parsimonious interface turbulence modeling approaches across operations demonstrates that the interfacial turbulence transport, and associated flow and thermal physics can be modeled with reasonable fidelity to predict at least some of the cryogenic tank operations in flight-sized tanks on large time scales in a practical manner.