Analysis of the relevance of the filtered radiative transfer equation terms for large eddy simulation of turbulence-radiation interaction

TL;DR

This paper investigates the importance of different terms in the filtered radiative transfer equation within large eddy simulations of turbulence-radiation interaction, highlighting when subgrid-scale modeling is necessary.

Contribution

It provides an analysis of the relevance of unclosed RTE terms in LES and evaluates the impact of neglecting subgrid-scale radiation fluctuations under various conditions.

Findings

Neglecting subgrid-scale radiation fluctuations is accurate for absorption terms.

Turbulence-radiation interaction effects grow with optical thickness and turbulence intensity.

Subgrid-scale modeling is needed for higher optical thickness and turbulence above 20%.

Abstract

An analysis of the turbulence-radiation interaction in the framework of large eddy simulation (LES) is presented. Direct numerical simulation (DNS) of statistical steady forced homogeneous isotropic turbulence is used to evaluate the relevance of the unclosed terms of the filtered radiative transfer equation (RTE) and to study the influence of parameters like the optical thickness and the turbulence intensity. LES without subgrid-scale models of the filtered RTE has also been investigated. Neglecting the subgrid-scale fluctuations of radiation has proved to be an accurate assumption in various cases, especially for the absorption terms of radiation. However, turbulence-radiation interaction effects increase significantly with the optical thickness based on the size of the filter or with the turbulence intensity, and consequently subgrid-scale modelling should be developed in cases where the optical thickness is not thin and the turbulence intensity higher than 20%.