Yan-Fei Jiang, James M. Stone, Shane W. Davis
We describe a numerical algorithm to integrate the equations of radiation
magnetohydrodynamics in multidimensions using Godunov methods. This algorithm
solves the radiation moment equations in the mixed frame, without invoking any
diffusion-like approximations. The moment equations are closed using a variable
Eddington tensor whose components are calculated from a formal solution of the
transfer equation at a large number of angles using the method of short
characteristics. We use a comprehensive test suite to verify the algorithm,
including convergence tests of radiation-modified linear acoustic and
magnetosonic waves, the structure of radiation modified shocks, and
two-dimensional tests of photon bubble instability and the ablation of dense
clouds by an intense radiation field. These tests cover a very wide range of
regimes, including both optically thick and thin flows, and ratios of the
radiation to gas pressure of at least 10^{-4} to 10^{4}. Across most of the
parameter space, we find the method is accurate. However, the tests also reveal
there are regimes where the method needs improvement, for example when both the
radiation pressure and absorption opacity are very large. We suggest
modifications to the algorithm that will improve accuracy in this case. We
discuss the advantages of this method over those based on flux-limited
diffusion. In particular, we find the method is not only substantially more
accurate, but often no more expensive than the diffusion approximation for our
intended applications.
View original:
http://arxiv.org/abs/1201.2223
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