Experimental investigation on flame patterns of buoyant diffusion flame in a large range of imposed circulations

Effects of circulation and buoyancy on the transition from a fire whirl to a blue whirl

“…This analysis showed that the BW was close to the extinction limit defined previously [4]. The BW formation limits, defined on the basis ofQ and , as well as the relationship between nondimensional heat-release rate (Q * D ) and nondimensional circulation ( * D ), were both sensitive to the gap size between the half-cylinders.…”

“…This extended map showed that the combinations ofQ and that led to blue-whirl formation were within the extinction limit defined in Ref. [4]. The formation of blue whirls in this region also requires experimental apparatus to satisfy surface-boundary conditions [8] that were absent in previous work.…”

“…Both the structure and the dynamic behavior of fire whirls are dominated by the effects of buoyancy, which arises from heat release, and by circulation, determined by the level of ambient swirl. In laboratory-scale experimental investigations, the combination of the heat-release rate (Q) and circulation ( ) can be controlled to determine the shapes of fire whirls, which have been classified into a number of regimes [4].…”

“…Lei et al [4] showed the influence ofQ and on the shape of fire whirls formed in an Emmonstype [2] fire-whirl apparatus where swirl is generated by a spinning mesh around a central flame. TheirQ-map showed the strong influence of on the overall shape of fire whirls, especially on the flame shape at the base.…”

“…Using fixed length scales (such as apparatus or burner diameter) in scaling analyses [4,23] results in quantities that denote general large-scale effects, for instance, the predictions of flame height of FWs for known values of andQ. The use of characteristic length scales derived from flame geometry represent effects of the local flow field.…”