A fully asymptotic preserving decomposed multi-group method for the frequency-dependent radiative transfer equations.

The opacity of FRTE depends on not only the material temperature but also the frequency, whose values may vary several orders of magnitude for different frequencies. The gray radiation diffusion and frequency-dependent diffusion equations are two simplified models that can approximate the solution to FRTE in the thick opacity regime. The frequency discretization for the two limit models highly affects the numerical accuracy. However, classical frequency discretization for FRTE considers only the absorbing coefficient. In this paper, we propose a new decomposed multi-group method for frequency discretization that is not only AP in both gray radiation diffusion and frequency-dependent diffusion limits, but also the frequency discretization of the limiting models can be tuned. Based on the decomposed multi-group method, a full AP scheme in frequency, time, and space is proposed. Several numerical examples are used to verify the performance of the proposed scheme. • The frequency discretization can be consistent with the required multi-group diffusion model. • Accuracy is guaranteed in both optically thin and thick regimes with large spatial meshes. • The required temporary step is independent of the light speed. • Nonlinearity appears only in the system with macroscopic quantities. • The microscopic quantities can be updated linearly. [ABSTRACT FROM AUTHOR]