A non-equilibrium surface reservoir approach for hybrid DSMC/Navier-Stokes particle generation

An approach for the generation of particles at a hybrid Navier-Stokes/DSMC interface is presented for simple gases and gas mixtures with internal degrees of freedom. DSMC particles generated at a hybrid boundary are assigned thermal velocities using a non-equilibrium surface reservoir approach, in which the fluxes of mass, momentum and energy determined from the Navier-Stokes solution are used to prescribe the appropriate velocity distribution function used in the DSMC particle generation. The non-equilibrium surface reservoir approach is first outlined for a simple (single-species, monatomic) gas, and is then extended to gas mixtures with internal degrees of freedom, in which additional diffusion and internal heat flux terms are included in the Generalized Chapman-Enskog formulation of the perturbation. The significance of the diffusion, shear stress and heat flux breakdown parameters used to compute the perturbation are examined at a hybrid interface within non-equilibrium boundary layer flow, as well as within the breakdown region near a normal shock, in a five-species air gas mixture. The validity of the Chapman-Enskog perturbation at each of these hybrid interfaces is assessed by comparison with the Generalized Chapman-Enskog perturbations. Although a hybrid flowfield solution is not presented, this work provides a rigorous approach for non-equilibrium particle generation involving general hybrid particle/continuum studies of hypersonic flows.