A Module for Radiation Hydrodynamic Calculations with ZEUS‐2D Using Flux‐limited Diffusion

A module for the ZEUS-2D code is described which may be used to solve theequations of radiation hydrodynamics to order unity in v/c, in the flux-limiteddiffusion (FLD) approximation. In this approximation, the tensor Eddingtonfactor f which closes the radiation moment equations is chosen to be anempirical function of radiation energy density. This is easier to implement andfaster than full-transport techniques, in which f is computed by solving thetransfer equation. However, FLD is less accurate when the flux has a componentperpendicular to the gradient in radiation energy density, and in opticallythin regions when the radiation field depends strongly on angle. The materialcomponent of the fluid is here assumed to be in local thermodynamicequilibrium. The energy equations are operator-split, with transport terms,radiation diffusion term, and other source terms evolved separately. Transportterms are applied using the same consistent transport algorithm as in ZEUS-2D.The radiation diffusion term is updated using an alternating-direction implicitmethod with convergence checking. Remaining source terms are advanced togetherimplicitly using numerical root-finding. However when absorption opacity iszero, accuracy is improved by treating compression and expansion source termsusing time-centered differencing. Results are discussed for test problemsincluding radiation-damped linear waves, radiation fronts propagating inoptically-thin media, subcritical and supercritical radiating shocks, and anoptically-thick shock in which radiation dominates downstream pressure.Comment: Accepted by ApJS; 30 pages, 11 figure