My collaborator Francis Filbet and myself just submitted a new paper, entitled A Hierarchy of Hybrid Numerical Methods for Multi-Scale Kinetic Equations.
In this paper, we construct a hierarchy of hybrid numerical methods for multi-scale kinetic equations based on moment realizability matrices, a concept introduced by Levermore, Morokoff and Nadiga. Following such a criterion, one can consider hybrid scheme where the hydrodynamic part is given either by the compressible Euler or Navier-Stokes equations, or even with more general models, such as the Burnett or super-Burnett systems.
We present applications of this method to the Boltmann equation for rarefied gases, in one dimension of space and three dimensions of velocity, for both Euler and Navier-Stokes fluid description. We prove numerically that our hierarchy of hybrid fluid-kinetic solvers can provide different numerical methods able to achieve the accuracy of a pure kinetic one, with efficiency sometimes almost comparable with the one of a fluid model.