  This paper aims at the simulation of multiple scale physics in the system of
radiation hydrodynamics. The system couples the fluid dynamic evolution
equations with the radiative heat transfer. The coupled system is solved by the
gas-kinetic scheme (GKS) for the compressible viscous and heat conducting flow
and the unified gas-kinetic scheme (UGKS) for the non-equilibrium radiative
transfer, together with the momentum and energy exchange between these two
phases. For the radiative transfer, due to the possible large variation of
fluid opacity in different regions, the transport of photons in the flow system
is simulated by the multiscale UGKS, which is capable of naturally capturing
the transport process from the free streaming to the diffusive
propagation.Since both GKS and UGKS are finite volume methods,all unknowns are
defined inside each control volume and are discretized consistently for the
hydrodynamic and radiative variables. For the coupled system, the scheme has
the asymptotical preserving (AP) property, such as recovering the equilibrium
diffusion limit for the radiation hydrodynamic equations in the optically thick
region, where the cell size is not limited by photon's mean free path. A few
test cases, such as radiative shock wave problems, are used to validate the
current approach.
