Formation of multiple fire whirls

Multiple fire whirls were formed from a controlled propane gas line fire placed between two parallel moving screens which impart a controlled shear to the ambient air. It was found that the line fire, breaks up into approximately equally spaced fire whirls after the attainment of certain critical conditions. Employing instability theory, a critical dimensionless parameter was obtained for the determination of the point of fire whirl formation, and governing dimensionless parameters were obtained to enable the spacing data of established whirls to be presented in a universal plot. By employing the whirl spacing data, a correlation was obtained for the variation in whirl height. The analysis yielded: o 1. The vorticity required for fire whirl development increases with buoyancy. 2. The characteristic spacing of the fire whirls increases with vorticity but decreases with increased buoyancy. 3. The behavior of the visible whirl height depended upon the vortex strength of and the fuel available to an individuel whirl: A) Small fuel supply: Whirl height is determined by the effectiveness of the fuel-air mixing, which is governed by the whirl vortex strength. The whirl height then increases with available vorticity, but decreases with increased fuel supply due to reduced circulation associated with a reduction in the characteristic spacing. B) Large fuel supply: The whirl height is governed by the quantity of fuel available to it. The whirl height, then, increases with both increased vorticity and with increased fuel supply.