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Flame self-interactions in an open turbulent jet spray flame

A three-dimensional direct numerical simulation database of an open turbulent jet spray flame representing a laboratory-scale burner configuration has been analyzed to investigate flame self-interactions (FSIs) in the presence of flow induced shear, to the best of the authors' knowledge, for the first time. The FSI occurrences [i.e., unburned gas mixture pockets (UBGPs), tunnel formations (TFs), tunnel closures (TCs), and burned gas mixture pockets (BGPs)] have been identified across the flame at different axial locations. It has been found that the interplays between turbulence, droplet evaporation, and chemistry have a significant influence on the topological nature of the flame surface. Close to the jet exit, the FSI events are found to occur toward the burned gas side of the flame, but moving further away from the jet exit, there are significant occurrences of FSI events within the flame where increasingly fuel-rich, low Damkohler number conditions occur. In this study, the FSI events have been found to be predominantly TFs and TCs, which is consistent with previous analyses of turbulent premixed flames and combustion of droplet-laden mixtures. However, non-negligible occurrences of UBGPs and BGPs are also observed in this case. The results obtained from this analysis have important implications from a modeling perspective where flame topologies have a significant influence on the nature of the flame surface, which will, in turn, affect the flame-surface based modeling approaches. Accordingly, the findings of the current analysis may need to be accounted for during the development of flame surface-based closures in the context of turbulent spray flames.