A hybrid continuum-particle solver for unsteady rarefied gas flows

• A hybrid continuum-particle solver for unsteady flows has been developed.
• Arbitrary geometries may be modeled and the domain decomposition is dynamic.
• Two different parallelization strategies have been applied.
• Validation has been performed for the problems of shock tube and orifice flow.
• Satisfactory agreement found with previous solutions at a tractable CPU cost.

The implementation of a hybrid simulation algorithm based on the compressible Navier–Stokes equations and the Direct Simulation Monte Carlo (DSMC) method is discussed, with emphasis on problems of transient nature. The coupling of the two methods at their common interface is achieved by the generation of particles according to the local Maxwellian distribution and the imposition of macroscopic quantities for the continuum solver. Dynamic characteristics of the continuum-particle decomposition scheme lead to a flexible and fully configurable determination of the two regions. The parallelization scheme and the ability to consider arbitrary geometries allow the consideration of the method for non-trivial, practical applications. The validation of the code is performed for two benchmark problems, namely those of shock tube flow and unsteady flow through an orifice.