Multilevel Method with Low-Order Equations of Mixed Types and Two Grids in Photon Energy for Thermal Radiative Transfer

TL;DR

This paper introduces a novel multilevel iterative method with two photon energy grids for efficiently solving coupled radiative transfer and material energy equations in high-energy physics applications.

Contribution

It presents a new nonlinear multilevel approach using low-order equations and dual energy grids, enhancing solution efficiency for complex radiative transfer problems.

Findings

Demonstrates convergence in Fleck-Cummings test with many energy groups

Uses fully implicit Euler for stable time integration

Effectively couples RTE with MEB equations in simulations

Abstract

Thermal radiative transfer (TRT) is an essential piece of physics in inertial confinement fusion, high-energy density physics, astrophysics etc. The physical models of this type of problem are defined by strongly coupled differential equations describing multiphysics phenomena. This paper presents a new nonlinear multilevel iterative method with two photon energy grids for solving the multigroup radiative transfer equation (RTE) coupled with the material energy balance equation (MEB). The multilevel system of equations of the method is formulated by means of a nonlinear projection approach. The RTE is projected over elements of phase space to derive the low-order equations of different types. The hierarchy of equations consists of (1) multigroup weighted flux equations which can be interpreted as the multigroup RTE averaged over subintervals of angular range and (2) the effective grey (one-group) equations which are spectrum averaged low-order quasidiffusion (aka variable Eddington factor) equations. The system of RTE, low-order and MEB equations is approximated by the fully implicit Euler time-integration method in which absorption coefficient and emission term are evaluated at the current time step. Numerical results are presented to demonstrate convergence of a multilevel iteration algorithm in the Fleck-Cummings test problem with Marshak wave solved with large number of photon energy groups.