The effects of coflow air swirl on the structure of strongly-pulsed, turbulent jet diffusion flames were examined experimentally. The dynamics of the large-scale flame structures, including the flame dimensions, the degree of flame structure interaction, and the turbulent flame puff celerity were determined from high-speed imaging of the luminous flame. The flames with swirl were found to have a visual flame length up to 34% shorter than non-swirling flames, depending on the fuel injection condition, the coflow flow rate, and the swirl intensity. The flame dimensions were impacted more by swirl for the cases of longer injection time and higher coflow flow rate. The flame puff separation generally decreased when swirl was imposed. The decreased flame length and flame puff separation are consistent with a greater momentum exchange between the flame and the surrounding coflow, leading to an increased rate of air entrainment. For most injection conditions, the flame puff celerity, both with and without swirl, increases as jet-off time decreases; the celerity decreases with downstream locations. The increased flame puff celerity is presumably due to the competition of each flame puff with its neighbors for the available coflow air. Swirl was seen to further decrease the flame puff celerity; this observed decrease in flame celerity also being consistent with an increased rate of air entrainment into the flame.
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