Extension of the Full Cavitation Model for Cryogenic Fluids

Abstract

The initial cavitation model, originally reported in 2000, has been successfully implemented within several CFD codes (CFD-ACE+, Fluent, ...) and applied throughout a variety of industrial applications. The objective of this study was to extend this model into cryogenic fluids and demonstrate its capability to simulate cryogenic propellant fed turbo pumps associated with liquid rocket engines. In the modeling approach described here the energy equation was modified to include the phase change effects due to cavitation. This necessitated variable physical properties, including vapor pressure, liquid density, vapor density, thermal conductivity, specific heat, fluid viscosity, surface tension, and evaporation heat for the cryogenic fluids. These properties were extracted from NIST tables which were implemented into the CFD-ACE+ computer code. Customized solution algorithm treatments were necessary to ensure robust numerical convergence as a result of the large variations in vapor pressure with respect to temperature typically present in cryogenic fluid pumping and diffusion phenomena. The Hord’s experiment was chosen for the validation as a result of its complete and comprehensive measurement set availability in the open literature. The calculated pressure and temperature profiles along a hydro foil, at different flow conditions for both nitrogen and hydrogen fluids, were compared with experimental measurements. Without any modification to the empirical constants, originally calibrated with water, the predicted results matched remarkably well with the experimental data. This effort has established a new standard compared to previous predictions for liquid nitrogen. For liquid hydrogen flows a significant improvement in the temperature recovery region compared to previous predictions is described and provides for an excellent baseline effort to improve upon.