Extending CFD Modeling to Near-Continuum Flows Using Enhanced Thermophysical Modeling

The constitutive relations found in traditional Navier-Stokes-based computational fluid dynamics solvers are known to be limited in altitude. The presence of nonequilibrium phenomena beyond what these methods are able to predict becomes more prevalent at higher altitudes, or increasing Knudsen number. The bulk viscosity, normally assumed to be zero in most computational fluid dynamics applications, is examined as a means of increasing the range of applicability of computational fluid dynamics. The bulk viscosity model used was from recent calculations available in the literature, from a new anisotropic potential energy surface, and is restricted to temperatures below 2000 K. The normal shock problem was solved for Mach numbers up to ten, using the bulk viscosity model. The bulk viscosity provided improvement in the agreement with observations of normal shock thickness for Mach numbers up to ten. Two axisymmetric, experimentally observed flows were solved with and without the bulk viscosity, and compared to DSMC solutions of a previous work. Improvement of surface heat transfer agreement with observation was found for a hollow-cylinder are axisymmetric body. Improvement of separation point prediction was found for an axisymmetric double cone