Kinetic modelling of rarefied gas flows with radiation

TL;DR

This paper introduces two kinetic models for high-temperature rarefied gas flows with radiation, capturing non-equilibrium dynamics and validated against simulations, with applications to various flow configurations including hypersonic flow.

Contribution

The paper presents two novel kinetic models for radiative rarefied gases, incorporating intermolecular potentials and relaxation approximations, and couples gas flow with radiation self-consistently.

Findings

Radiation significantly affects heat transfer on obstacles.

Models accurately predict non-equilibrium flow behaviors.

Radiation influence depends on photon Knudsen number and radiation strength.

Abstract

Two kinetic models are proposed for high-temperature rarefied (or non-equilibrium) gas flows with radiation. One of the models uses the Boltzmann collision operator to model the translational motion of gas molecules, which has the ability to capture the influence of intermolecular potentials, while the other adopts the relaxation time approximations, which has higher computational efficiency. In the kinetic modelling, not only the transport coefficients such as the shear/bulk viscosity and thermal conductivity but also their fundamental relaxation processes are recovered. Also, the non-equilibrium dynamics of gas flow and radiation are coupled in a self-consistent manner. The two proposed kinetic models are first validated by the direct simulation Monte Carlo method in several non-radiative rarefied gas flows, including the normal shock wave, Fourier flow, Couette flow, and the creep flow driven by the Maxwell demon. Then, the rarefied gas flows with strong radiation are investigated, not only in the above one-dimensional gas flows, but also in the two-dimensional radiative hypersonic flow passing cylinder. In addition to the Knudsen number of gas flow, the influence of the photon Knudsen number and relative radiation strength is scrutinised. It is found that the radiation can make a profound contribution to the total heat transfer on obstacle surface.