ZEUS-2D - A RADIATION MAGNETOHYDRODYNAMICS CODE FOR ASTROPHYSICAL FLOWS IN 2 SPACE DIMENSIONS .3. THE RADIATION HYDRODYNAMIC ALGORITHMS AND TESTS

In this, the third of a series of three papers, we conclude a detailed description of ZEUS-2D, a numerical code for the simulation of fluid dynamical flows in astrophysics including a self-consistent treatment of the effects of magnetic fields and radiation transfer. In this paper, we describe the radiation hydrodynamical (RHD) algorithms in ZEUS-2D. We develop a two-dimensional full transport algorithm to evolve the radiation moment equations. The moment equations are closed with the tensor variable Eddington factor whose components are computed from angular quadratures of the specific intensity which, in tum, is computed from a formal solution of the two-dimensional transfer equation using the method of short characteristics. This algorithm for multidimensional RHD differs significantly from more commonly used methods based on the diffusion approximation. The results of a collection of test problems we have developed for RHD algorithms are presented.