The nonlinear radiative transfer model coupling the radiative transfer equation (RTE) and material energy balance equation has been widely studied in many problems such as inertial confinement fusion. Due to factors such as material properties, the optical thickness may vary across several orders of magnitude, resulting in strongly multiscale transport characteristics that pose significant challenges for numerical simulations. In this work, an asymptotic preserving (AP) scheme based on the discrete unified gas kinetic scheme (DUGKS) framework is proposed. The microscopic RTE is solved by a simplified DUGKS, where the cell interface intensity is simply constructed from the averaging along the characteristic line, and the macroscopic material energy balance equation is solved by a finite volume method consistent with the DUGKS. The time-marching of the present method exhibits the implicit characteristic, and the mesh size is not strictly constrained by the photon mean free path. As a result, the present method has the AP property. Theoretical analysis is conducted to prove the AP property, and several single- and multi-scale tests are carried out to confirm the accuracy and robustness of the present method.

Nonlinear radiative transfer system, Asymptotic preserving, Discrete unified gas kinetic scheme