Multi-scale Simulations of Gas Flows with Unified Flow Solver

The Boltzmann kinetic equation links micro- and macroscale descriptions of gases. This paper describes multi-scale simulations of gas flows using a Unified Flow Solver (UFS) based on the Boltzmann equation. A direct Boltzmann solver is used for microscopic simulations of the rarefied parts of the flows, whereas kinetic CFD solvers are used for the continuum parts of the flows. The UFS employs an adaptive mesh and algorithm refinement procedure for automatic decomposition of computational domain into kinetic and continuum parts. The paper presents examples of flow problems for different Knudsen and Mach numbers and describes future directions for the development of UFS technology.