Analysis of near wall flame and wall heat flux modeling in turbulent premixed combustion

TL;DR

This paper investigates flame-wall interactions in turbulent premixed combustion through DNS, proposing a new predictive wall heat flux model validated against simulations, with insights into flame structure and curvature effects near walls.

Contribution

It introduces a novel species alignment index and a predictive wall heat flux model based on fundamental DNS insights into near-wall flame behavior.

Findings

Larger flame curvatures correlate with lower vorticity magnitude.

Alignment of the progress variable gradient with the most compressive eigenvector is consistent near walls.

The proposed heat flux model shows good agreement with DNS data.

Abstract

Reactive flows in confined spaces involve complex flame-wall interaction (FWI). This work aims to gain more insights into the physics of the premixed near-wall flame and the wall heat flux as an important engineering relevant quantity. Two different flame configurations have been studied, including the normal flushing flame and inclined sweeping flame. By introducing the skin friction vector defined second-order tensor, direct numerical simulation (DNS) results of these two configurations show consistently that larger flame curvatures are associated with small vorticity magnitude under the influence of the vortex pair structure. Correlation of both the flame normal and tangential strain rates with the flame curvature has also been quantified. Alignment of the progress variable gradient with the most compressive eigenvector on the wall is similar to the boundary free behavior. To characterize the flame ordered structure, especially in the near-wall region, a species alignment index is proposed. The big difference in this index for flames in different regions suggests distinct flame structures. Building upon these fundamental insights, a predictive model for wall heat flux is proposed. For the purpose of applicability, realistic turbulent combustion situations need to be taken into account, for instance, flames with finite thickness, complex chemical kinetics, non-negligible near-wall reactions, and variable flame orientation relative to the wall. The model is first tested in an one-dimensional laminar flame and then validated against DNS datasets, justifying the model performance with satisfying agreement.