Treatment of long-range interactions arising in the Enskog-Vlasov description of dense fluids

Abstract

The kinetic theory of rarefied gases and numerical schemes based on the Boltzmann equation have evolved to the cornerstone of non-equilibrium gas dynamics. However, their counterparts in the dense regime remain rather exotic for practical non-continuum scenarios. This problem is partly due to the fact that long-range interactions arising from the attractive tail of molecular potentials, lead to a computationally demanding Vlasov integral. This study focuses on numerical remedies for efficient stochastic particle simulations based on the Enskog-Vlasov kinetic equation. In particular, we devise a Poisson-type elliptic equation that governs the underlying long-range interactions. The idea comes through fitting a Green function to the molecular potential, and hence deriving an elliptic equation for the associated fundamental solution. Through this transformation of the Vlasov integral, efficient Poisson-type solvers can be readily employed in order to compute the mean field forces. Besides the technical aspects of different numerical schemes for the treatment of the Vlasov integral, simulation results for the evaporation of a liquid slab into the vacuum are presented. It is shown that the proposed formulation leads to accurate predictions with a reasonable computational cost.