An investigation of non-equilibrium heat transport in a gas system under external force field

TL;DR

This paper introduces a unified gas-kinetic scheme (UGKS) for modeling non-equilibrium heat transport in gases under external forces, effectively capturing multiscale physics from particle transport to hydrodynamics.

Contribution

The development of a well-balanced UGKS that adapts across scales to accurately simulate non-equilibrium gas flows under external forces is the paper's main novelty.

Findings

UGKS can recover multiscale flow physics from particle to continuum regimes.

Theoretical analysis shows external forces significantly influence non-equilibrium heat transport.

The scheme effectively models the complex behavior of gases in external force fields.

Abstract

The gas dynamics under external force field is essentially associated with multiple scale nature due to the large variations of density and local Knudsen number. Single scale fluid dynamic equations, such as the Boltzmann and Navier-Stokes equations, are valid in their respective modeling scales, and it is challenging for the modeling and computation of a multiple scale problem across different regimes and capture the corresponding non-equilibrium flow physics. Based on the direct modeling of conservation laws in the discretized space, a well-balanced unified gas-kinetic scheme (UGKS) for multiscale flow transport under external force field has been developed and is used in the current study of non-equilibrium gaseous flow under external force field. With the variation of modeling scale, i.e., the cell size and time step, the UGKS is able to recover cross-scale flow physics from particle transport to hydrodynamic wave propagation. Theoretical analysis based on the kinetic model equation is presented to conceptually illustrate the effects of external force on the non-equilibrium heat transport.