Fire whirls: A Combustion Science Perspective

ABSTRACT

Fire whirls occur in urban and wildland fires, intensifying the local burning rate and generating long-distance firebrands. A striking feature of fire whirls is their increased flame heights, and this article provides a review of previous efforts to understand how the height of a fire whirl is determined. This paper mainly discusses four factors that influence fire-whirl height: burning rate, strong vorticity, turbulence reduction, and vortex breakdown. It is shown that each influence can be understood based on a simple constant-density mixture-fraction model. In the constant-density approximation, the flame shape can be analyzed in a prescribed flow field. This paper considers a one-celled Burgers vortex, a two-celled Sullivan vortex, and a strong-vorticity flow in which the axial velocity near the axis of rotation is faster than that in the peripheral region.

KEYWORDS:

• Fire whirl
• mixture-fraction theory
• burgers vortex
• Sullivan vortex
• vortex breakdown

Funding

This work was supported by the Japan Society for the Promotion of Science [JP19H01807, JP19K22023, JP19K03672]; the Japanese Ministry of Education, Culture, Sports, Science and Technology [World Premier International Research Center Initiative]; Kyushu University [FY2021 IMI Joint Usage Research Program].

Nomenclature

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Acknowledgments

The authors thank Kozo Sekimoto and Yuji Nakamura for technical discussion. We also thank Takumi Takahashi for providing photographs of open-field experiments. A part of this study was supported by JSPS KAKENHI Grant Numbers JP19H01807, JP19K22023, and JP19K03672, and by World Premier International Research Center Initiative (WPI), MEXT, Japan. Also, this work was partly supported by 2021 IMI Joint Research Program of Institute of Mathematics for Industry, Kyushu University (MEXT Joint Usage/Research Center).

Disclosure statement

No potential conflict of interest was reported by the author(s).