by: Jason A. Sutula

In 1923, the Great Kantō Earthquake struck Japan with devastating force. Mountains moved, buildings crumbled, and people watched helplessly as one of the most powerful earthquakes on record stole their villages, towns, and loved ones. Adding insult to injury, the earthquake hit at midday as many people were preparing meals at the family hearth within their homes. Small fires erupted throughout the countryside and quickly spread into devastating wildfires. Firestorms and fire whirls were also recounted in tales told by the survivors. One fire whirl in particular claimed the lives of 38,000 people who had taken shelter in a building in downtown Toyko.

Fortunately, fire whirls are extremely rare. These swirling pillars of fire can be formed within naturally occurring wildfires or post-disaster fires. Certain conditions must exist for a fire whirl to develop. In particular, there must be an organized source of angular momentum to produce the swirling velocities necessary to create the whirl.

Emmons and Ying [1] were two of the earliest researchers who attempted to quantify the fire science behind the development of a fire whirl. Using a flaming pool of acetone, they spun a cylindrical screen around the resulting fire in order to produce a measurable vorticity. Two conclusions were reached. First, the radius of the fire whirl will shrink as it spins faster. Second, as the fire whirl spin increases, the temperature within the fire plume also increases.

Researchers at both the Department of Fire Protection Engineering at the University of Maryland and the Building Fire Research Laboratory at the National Institute of Standards and Technology have expanded on the foundation laid by Emmons and Ying. Battaglia, McGrattan, Rehm, and Baum [2] conducted a large-eddy numerical analysis and mapped out the flame-stretched structure of a fire whirl. Through computational fluid dynamics, they demonstrated that the rotation of the velocities surrounding the fire will structurally change the shape of the flames and bend them to its will.

In an effort not to be outdone, Assistant Professor Michael Gollner created his own fire whirl in his laboratory at the University of Maryland. The youtube video in this post was shot with a 300 frame per second high speed camera that captured a fire whirl created from a burning heptane pool situated within a specially designed compartment that added the necessary vorticity.

[1] Emmons, H.W. and Ying, S.J., Proc. 11th Int. Symp. on Combustion, Pittsburg, PA, Combustion Institute, pp 473-88, 1967.

[2] Battaglia, F., McGrattan, K., Rehm, R., and Baum, H., “Simulating Fire Whirls,” Combustion Theory Modelling, Vol. 4., pp. 123-138, 2000.

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Comments
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