Gas-Kinetic Simulation of Separated Flows

This SBIR project proposes to develop a gas-kinetic CFD solver for separated flow simulation. Compared with the traditional macroscopic CFD approach, a gas-kinetic CFD approach is more suitable for turbulent separated flow simulation. This is because a gas-kinetic model with the turbulence relaxation time can represent rich and complex physics when projected onto hydrodynamic variables and the turbulence relaxation time naturally includes both the regular viscous effects and higher-order modifications. Unlike the traditional macroscopic CFD approach, the gas-kinetic CFD approach calculates the hydrodynamics fluxes across the surface near the walls based on the non-equilibrium particle distribution function without invoking any approximation to gradient information. This implementation of the wall boundary conditions has been found as the key for success of the gas-kinetic CFD approach for turbulent flow simulation. In Phase I, we will first systematically investigate the benefits of including the higher-order terms of the Chapman-Enskog expansion beyond the Navier-Stokes level for turbulent separated flow simulations. This will lay a solid foundation for fully development of an innovative gas-kinetic CFD solver for improved separated flow simulation in Phase II.