Unified solver for rarefied and continuum flows with adaptive mesh and algorithm refinement

This paper describes a Unified Flow Solver (UFS) for rarefied and continuum gas flows. The UFS separates the rarefied and continuum flow domains and selects appropriate solvers to combine the efficiency of continuum models with the accuracy of kinetic models. The direct numerical solution of the Boltzmann transport equation is used in rarefied regions, while kinetic schemes of continuum fluid dynamics are used elsewhere. Using similar computational techniques for the kinetic and continuum solvers, and employing intelligent domain decomposition algorithms attain the efficiency and numerical stability of the UFS. Solutions of test problems are presented to illustrate the capabilities of the UFS for high and low speed flows. It is shown that the UFS can dynamically adapt the computational mesh and automatically introduce and remove kinetic patches to provide significant savings by limiting molecular scale solutions only to the regions where they are needed.