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This paper experimentally analyzes the simultaneous influence of heat releaseand coherent vortex structures on the transfer of kinetic energy across scalesaround the laminar flame thickness $\delta^0_\mathrm{L}$ in a turbulentpremixed swirl flame and a non-reacting swirl flow. High-resolution tomographicparticle image velocimetry and formaldehyde planar laser induced fluorescencemeasurements are used to obtain 3D velocity fields and estimates of theprogress variable and density fields. The kinetic energy transfer across afilter scale of $\Delta = 1.5 \delta^0_\mathrm{L}$ was then quantified usingphysical space analysis. Coherent flow structures were identified using theswirling strength and proper orthogonal decomposition was used to identify thedominant periodic flow structure. While non-reacting regions of the flow showmean down-scale energy transfer (forward-scatter), mean back-scatter isobserved internal to the flame. Importantly, the back-scatter magnitude in theflame increases in regions undergoing flame/vortex interaction. That is, themean back-scatter magnitude at locations simultaneously inside the flame and alarge-scale coherent vortex is higher than regions in the flame and not in avortex, with the mean back-scatter magnitude increasing with the swirlingstrength. This increased back-scatter may be due to locally higher heat releaserates in locations of flame/vortex interaction. Overall, the resultsdemonstrate the importance of kinetic energy back-scatter at scales around theflame thickness and the complicated relationship between back-scatter and localflame/flow structure; these results should be considered when modelingturbulence in flames.

Cross-scale turbulent kinetic energy transfer in the presence of coherent structures in premixed swirl combustion