Rarefied regime

Mon regime ne marche pas

In this paper, we propose a BGK model which is consistent with any arbitrary constitutive laws, and which is designed to make high temperature gas flow simulations in the rarefied regime. A Chapman-Enskog analysis gives the corresponding transport coefficients. Our approach is illustrated by a numerical comparison with a compressible Navier-Stokes solver with rotational and vibrational non equilibrium. The BGK approach gives a deterministic solver with a computational cost which is close to that of a simple monoatomic gas.

Keywords : rarefied gas dynamics BGK model polyatomic gas real gas effect second principle.

A BGK model for high temperature rarefied gas flows

Have you forgotten your login? Direction des applications militaires. Hide details. Abstract : High temperature gases, for instance in hypersonic reentry flows, show complex phenomena like excitation of rotational and vibrational energy modes, and even chemical reactions. For flows in the continuous regime, simulation codes use analytic or tabulated constitutive laws for pressure and temperature.

This thesis focuses on analytical, numerical and experimental investigations on moderate rarefied gas flows through microchannels, for which the local equilibrium assumption is no longer valid. A specific experimental setup has been developed for measuring gas microflowrates under controlled temperature and pressure conditions. The experimental flowrate data of monatomic gases Ar and He and their mixtures through rectangular microchannels are compared in the slip flow regime with data from continuum models associated with second-order boundary conditions, and in the transition regime with data from the linearized Boltzmann equation.

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The collision term of the Boltzmann equation is given by the BGK model for monatomic gases and by the McCormack model for gas mixtures. It is clearly pointed out that the validity of the continuum approach is limited to average Knudsen numbers less than 0.

On the other hand, the kinetic models show an excellent agreement with the experimental data for monatomic gases in the whole considered Knudsen range, assuming diffuse reflection at the wall. However, for the mixtures in higher rarefied regimes, deviations occur; further investigations will be required for more definitive conclusions.