Non-parametric wall model and methods of identifying boundary conditions for moments in gas flow equations

Abstract : In this paper, we use Molecular Dynamics (MD) simulation method to study gas-wall boundary conditions. Discrete scattering information of gas molecules at the wall surface are obtained from collision simulations. The collision data can be used to identify the accommodation coefficients for parametric wall models such as Maxwell, Cercignani-Lampis scattering kernels. Since these scattering kernels are based on a limited number of accommodation coefficients, we adopt non-parametric statistical methods to construct the kernel to overcome these issues. Different from parametric kernels, the non-parametric kernels require no parameter (i.e accommodation coefficients) and no predefined distribution. We also propose approaches to derive directly the Navier friction and Kapitza thermal resistance coefficients as well as other interface coefficients associated to moment equations from the non-parametric kernels. The methods are applied successfully to systems composed of CH 4 or CO 2 and graphite, which are of interest to the petroleum industry.