Unified Methodology for Simulation of Continuum and Rarefied Flows

We propose to develop a stand-alone computational module for seamlessly extending the validity of continuum CFD codes into transitional and rarefied flow regimes. The module will be designed for implementation in to existing legacy codes for use in characterization of high altitude plume flows. The approach is based on a novel, regularized set of Navier-Stokes equations (RNS) that is extended to account for kinetic effects (intermediate Knudsen number, fluctuations) in the continuum approximation. RNS has several important features not found in classical NS equations that are of direct relevance high altitude plume flows: (a) Natural accounting of both continuum and rarefied gas flow regimes; and (b) Kolmogorov-scale field fluctuations resulting from a mathematical model that accounts for turbulent diffusion in a natural manner that allows direct simulation of phenomena such as laminar-turbulence transition and wall slip effects. Phase I will focus on development of a stand-alone, computational module prototype incorporating the RNS approach. The module will be connected to a characteristics-based high order compressible flow code with particle transport capabilities and will be exercised and evaluated against experimental data for a model problem that contains elements of both continuum and rarefied flows. Phase II will couple the module to flow and radiation codes used by MDA.