Periodic Structures in Pool Fires

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Large vortical structures have been observed to form at the base of moderate sized fires and to propagate upwards as the fuel and air are mutually consumed. This research seeks to understand how and why these structures form, to quantify their effect on the entrainment of air and the burning rate of the fuel, and to identify the similarities and differences in the near-field fluid mechanics among pool fires, strongly buoyant nonreacting jets, and natural convection above heated horizontal surfaces. Simultaneous measurements are made of the fluctuating concentration and velocity at multiple locations inside a large, low speed helium jet flowing vertically into air to simulate a pool fire. The fluctuating temperature and velocity are measured also above burning alcohol pools up to nearly one meter in diameter. A three-dimensional, transient numerical model of the nonreacting system is being developed to interpret the experimental results. The results of this research will provide a quantitative basis for the prediction of pool fires. Because it will be based on the fundamental interpretation of results from medium-sized plumes experiments, such understanding will be applicable also to fires of larger dimensions, which are of frequent concern to the community (spills, fuel tanks, etc...).