Unified Kinetic Approach for Simulations of Gas Flows in Rarefied and Continuum Regimes

Flow fields characterized by the simultaneous presence of continuum and rarefied regimes arise in many important applications, including re-entry of aerospace vehicles and micro-fluidics. This project aims to develop a commercial Unified Flow Solver (UFS) that automatically switches between and couples the continuum-fluid-dynamics and kinetic solvers needed for these two regimes. The UFS will maximize computational efficiency, and ensure numerical accuracy, stability, and robustness by employing intelligent domain decomposition algorithms and solution-adaptive mesh refinement. The Direct Numerical Solver (DNS) of the Boltzmann Transport Equation (BTE) developed and demonstrated in Phase I will be used in regions of moderate and high local Knudsen number, while a Navier-Stokes Solver will be used elsewhere. DNS offers unique advantages compared to DSMC methods for building hybrid codes. Kinetic schemes of gas dynamics will also be used to facilitate automatic domain decomposition for coupling the BTE and Navier-Stokes solvers. In the Knudsen layers, the grid size will be smaller than the characteristic mean free path while in the continuum domains it will be much larger than the mean free path. The advantages of the UFS methodology will be demonstrated for several actual aerospace, material processing, and micro-fluidics problems.