Thermal lattice Boltzmann simulations for multi-species fluid equilibration

Summary form only given. One of the goals of divertor physics is to model the interaction between neutrals and the plasma by a coupled UEDGE/Navier-Stokes system of solvers. An inverse statistical approach is to replace these highly nonlinear macroscopic equations by two coupled linear lattice BGK kinetic equations-which, in the Chapman-Enskog limit, will recover the original nonlinear two-fluid system. While the dimensionality has been increased from (x,t) to the kinetic phase space, the thermal lattice Boltzmann (TLBM) approach seeks to minimize (and discretize) the required degrees of freedom that must be preserved in /spl xi/-space. For example, on a 2D hexagonal lattice one can recover the nonlinear conservation equation of mass, momentum and energy with just 13 bits of /spl xi/-space information for each spatial grid point. Thus while the storage requirements for TLBM is increased by a factor of 3 over conventional CFD, there are substantial computational gains by moving to this linear kinetic representation: (a) Lagrangian free-streaming kinetic codes will apply to local operations, and (b) the avoidance of the nonlinear Riemann problem of CFD. The immediate parallelization and vectorization of TLBM codes makes them ideal for multi-PE platforms like T3E. There are also physics reasons for pursuing this kinetic imbedding. In the tokamak divertor one encounters time varying regimes in which the neutral collisionalities range from the highly collisional (and hence fluid regime) to the weakly collisional (well treated by Monte Carlo methods). The coupling of fluid-kinetic actions is a numerically stiff problem. However, by replacing the fluid representation by TLBM, one will be coupling two kinetic codes with non-disparate length and time scales. Here we shall present some 2D thermal simulations of interacting double shear layers in two species systems with mass ratios of 10 and density ratios of 3.