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

Reactive flows in confined space involve complex flame–wall interaction. 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 turbulent 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 friction vorticity magnitude under the influence of the friction 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 behaviour. To characterise the flame alignment structure, especially in the near-wall region, a species alignment index is proposed. Difference in this index suggests a distinct flame alignment structure in different near-wall regions. Building upon these fundamental insights, a predictive model for the 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.