Switching criteria for hybrid rarefied gas flow solvers

D.A. Lockerby, J.M. Reese, H. Struchtrup

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Switching criteria for hybrid hydrodynamic/molecular gas flow solvers are developed, and are demonstrated to be more appropriate than conventional criteria for identifying thermodynamic non-equilibrium. For switching from a molecular/kinetic solver to a hydrodynamic (continuum-fluid) solver, the criterion is based on the difference between the hydrodynamic near-equilibrium fluxes (i.e. the Navier-Stokes stress and Fourier heat flux) and the actual values of stress and heat flux as computed from the molecular solver. For switching from hydrodynamics to molecular/kinetic, a similar criterion is used but the values of stress and heat flux are approximated through higher order constitutive relations; in this case, we use the R13 equations. The efficacy of our proposed switching criteria is tested within an illustrative hybrid kinetic/Navier-Stokes solver. For the test cases investigated, the results from the hybrid procedure compare very well with the full kinetic solution, and are obtained at a fraction of the computational cost.
Original languageEnglish
Pages (from-to)1581-1598
Number of pages18
JournalProceedings A: Mathematical, Physical and Engineering Sciences
Issue number2105
Publication statusPublished - 8 May 2009


  • switching criteria
  • hybrid rarefied gas flow solvers
  • gas flow
  • local Knudsen number
  • breakdown parameter
  • hybrid code

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