Rarefaction Effects on the Outflow Boundary Conditions for External Subsonic Flows

Celenligil M. C.

26th International Symposium on Rarefied Gas Dynamics (RGD26), Kyoto, Japan, 20 June - 25 July 2008, vol.1084, pp.317-322 identifier

  • Publication Type: Conference Paper / Full Text
  • Volume: 1084
  • City: Kyoto
  • Country: Japan
  • Page Numbers: pp.317-322


In continuum-flow simulations, subsonic outflow boundary conditions are controlled solely by the Mach number. Such boundary conditions are not suitable for rarefied flows, and it is necessary to include the Knudsen number into them. In the present study, this is done for external flows, by introducing a simple model which adjusts the macroscopic boundary properties (from which the incoming molecules are calculated) according to the local rarefaction. A bridging formula is used between the continuum and free-molecule limits, and the results show considerable improvement in the rarefied-flow simulations.