CASTRO: A New Compressible Astrophysical Solver. II. Gray Radiation   Hydrodynamics
  We describe the development of a flux-limited gray radiation solver for the compressible astrophysics code, CASTRO. CASTRO uses an Eulerian grid with block-structured adaptive mesh refinement based on a nested hierarchy of logically-rectangular variable-sized grids with simultaneous refinement in both space and time. The gray radiation solver is based on a mixed-frame formulation of radiation hydrodynamics. In our approach, the system is split into two parts, one part that couples the radiation and fluid in a hyperbolic subsystem, and another parabolic part that evolves radiation diffusion and source-sink terms. The hyperbolic subsystem is solved explicitly with a high-order Godunov scheme, whereas the parabolic part is solved implicitly with a first-order backward Euler method. 
W. Zhang (LBNL), L. Howell (LLNL), A. Almgren (LBNL), A. Burrows   (Princeton), and J. Bell (LBNL)
astro-ph.IM astro-ph.HE astro-ph.SR physics.comp-ph