An optimized discrete unified gas kinetic scheme for radiative heat transfer

Radiative heat transfer in strongly inhomogeneous media is challenging because free transport, absorption, emission, and scattering interact across disparate spatial, angular and temporal scales. In this paper, A node-based optimized discrete unified gas kinetic scheme (DUGKS) for the transient radiative transfer equation in discrete-ordinates form is proposed. Within a finite volume discretization, transport and scattering processes are coupled through nodal half-time-step flux reconstruction rather than original interface center flux reconstruction, while an explicit time-marching procedure is retained. The method is validated using 8 cases involving parallel-plane medium subjected to diffuse radiation, two-layer media exposed to a collimated pulse, infinite slab with a Gaussian-shaped radiative source term, plane-parallel slab with an inclusion layer subjected to diffuse radiation, vacuum-gapped media subjected to diffuse radiation, vacuum-gapped media exposed to a collimated pulse, square enclosure with a homogeneous anisotropic scattering inclusion, and square enclosure with diffuse gray walls. The optimized DUGKS captures radiation-front propagation, localized steep gradients, interfacial transitions, transient reflectance and transmittance, with good agreement against analytical and reference solutions. The reported CPU times are approximately 51% lower than those of the original DUGKS. These results indicate that the method provides an effective numerical framework for radiative heat transfer.