Dynamic coupling of kinetic and continuum solvers for micro gas flow computations

A hybrid method, dynamic coupling the direct numerical solution of the Bhatnagar-Gross-Krook (BGK) kinetic equation and hydrodynamic Navier-Stokes equations is presented. The decomposition of the physical domain into kinetic and hydrodynamic sub-domains is based on the local Knudsen number and macroparameters gradients. The size of these domains will change during the evolution depending on the current value of the criteria. The solution is advanced in time simultaneously in both kinetic and hydrodynamic domains the coupling is achieved by matching half fluxes at the interface of the kinetic and Navier-Stokes domains, thus taking care of the conservation of momentum, energy and mass through the interface. Solver efficiency is increased via MPI (Message Passing Interface) parallelization. The accuracy and properties of the proposed method is assessed via successful computation of the flow through a slit, at pressure ratio of 0.5 and for wide range of Knudsen number.