Kinetic model and numerical method for multispecies radiation hydrodynamic system with multiscale nonequilibrium transport

This paper presents a comprehensive numerical framework for simulating radiation-plasma systems. The radiative transfer process spans multiple flow regimes due to varying fluid opacity across different regions, necessitating a robust numerical approach. We employ the multiscale unified gas-kinetic scheme (UGKS), which accurately captures photon transport phenomena from free streaming to diffusive wave propagation. The UGKS is also applied to the fluid model to address the significant mass disparity between electrons and ions, and their associated transport characteristics in both equilibrium continuum and non-equilibrium rarefied regimes. Our model explicitly incorporates momentum and energy exchanges between radiation and fluid fields in the coupled system, enabling detailed analysis of the complex interactions between electromagnetic and hydrodynamic phenomena. The developed algorithm successfully reproduces both optically thin and optically thick radiation limits while capturing the complex multiscale nonequilibrium dynamics of the coupled system. This unified treatment eliminates the need for separate numerical schemes in different regimes, providing a consistent and computationally effcient approach for the entire domain. The effectiveness and versatility of this approach are demonstrated through extensive numerical validation across a wide range of physical parameters and flow conditions.