A Small-Scale Study of Fire Whirls and Investigation of the Effects of Near-Ground Height on the Behavior of Fire Whirls

Authors: M. Arabghahestani, A. Darwish Ahmad, N. K. Akafuah

Abstract:

In this work, small-scale experiments of fire whirl were conducted to study the spinning fire phenomenon and to gain comprehensive understandings of fire tornadoes and the factors that affect their behavior. High speed imaging was used to track the flames at both temporal and spatial scales. This allowed us to better understand the role of the near-ground height in creating a boundary layer flow profile that, in turn contributes to formation of vortices around the fire, and consequent fire whirls. Based on the results obtained from these observations, we were able to spot the differences in the fuel burning rate of the fire itself as a function of a newly defined specific non-dimensional near-ground height. Based on our observations, there is a cutoff non-dimensional height, beyond which a normal fire can be turned into a fire whirl. Additionally, the results showed that the fire burning rate decreases by moving the fire to a height higher than the ground level. These effects were justified by the interactions between vortices formed by, the back pressure and the boundary layer velocity profile, and the vortices generated by the fire itself.

Keywords: Boundary layer profile, fire whirls, near-ground height, vortex interactions.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.3455587

References:

[1] T. Terada, Reports on whirls generated on September 1, 1923, Report of the Earthquake Prevention Committee No. 1001925, pp. 275.
[2] F.A.J.P.i.E. Williams, C. Science, Urban and wildland fire phenomenology, 8 (1982) 317-354.
[3] S. Soma, K.J.C. Saito, Flame, Reconstruction of fire whirls using scale models, 86 (1991) 269-284.
[4] C.H.J.W. Ebert, The meteorological factor in the Hamburg fire storm, 16 (1963) 70-75.
[5] H.B. Clements, Liftoff of Fire Brands, Final Report FS-SE-2106-2-4, U. S. Forest Service, Southeast Forest Experiment Station, Division of Fire, Recreation, Range and Wildlife Habitat Research, Macon, GA, (1970).
[6] S. Lee, F. Otto, Gross vortex activities in a simple simulated urban fire Symposium (International) on Combustion, Elsevier, 1975, pp. 157-162.
[7] C.M.J.R.P.R.-R.-B. Countryman, CA: Pacific Southwest Forest, F.S. Range Experiment Station, US Department of Agriculture, p, Mass fires and fire behavior, 19 (1964).
[8] H.E.J.B.o.t.A.M.S. Graham, Fire whirlwinds, (1955) 99-103.
[9] R.I. Emori, K.J.F.T. Saito, Model experiment of hazardous forest fire whirl, 18 (1982) 319-327.
[10] Y. Hayashi, K. Kuwana, R.J.F.S.S. Dobashi, Influence of vortex structure on fire whirl behavior, 10 (2011) 671-679.
[11] K. Kuwana, S. Morishita, R. Dobashi, K.H. Chuah, K.J.P.o.t.C.I. Saito, The burning rate’s effect on the flame length of weak fire whirls, 33 (2011) 2425-2432.
[12] J. Lei, N.J.F.S.J. Liu, Flame precession of fire whirls: a further experimental study, 79 (2016) 1-9.
[13] K. Zhou, N. Liu, J.S. Lozano, Y. Shan, B. Yao, K.J.P.o.t.C.I. Satoh, Effect of flow circulation on combustion dynamics of fire whirl, 34 (2013) 2617-2624.
[14] J. Lei, N. Liu, L. Zhang, H. Chen, L. Shu, P. Chen, Z. Deng, J. Zhu, K. Satoh, J.L.J.P.o.t.C.I. de Ris, Experimental research on combustion dynamics of medium-scale fire whirl, 33 (2011) 2407-2415.
[15] J. Lei, N. Liu, L. Zhang, Z. Deng, N.K. Akafuah, T. Li, K. Saito, K.J.C. Satoh, Flame, Burning rates of liquid fuels in fire whirls, 159 (2012) 2104-2114.
[16] J. Lei, N. Liu, J.S. Lozano, L. Zhang, Z. Deng, K.J.P.o.t.C.I. Satoh, Experimental research on flame revolution and precession of fire whirls, 34 (2013) 2607-2615.
[17] K.H. Chuah, K. Kuwana, K.J.C. Saito, Flame, Modeling a fire whirl generated over a 5-cm-diameter methanol pool fire, 156 (2009) 1828-1833.
[18] K.H. Chuah, K. Kuwana, K. Saito, F.A.J.P.o.t.C.I. Williams, Inclined fire whirls, 33 (2011) 2417-2424.
[19] G.M. Byram, R.E.J.F.S. Martin, The modeling of fire whirlwinds, 16 (1970) 386-399.
[20] H. Yu, S. Guo, M. Peng, Q. Li, J. Ruan, W. Wan, C.J.P.E. Chen, Study on the influence of air-inlet width on fire whirls combustion characteristic, 62 (2013) 813-820.
[21] P.J.F.S.S. Thomas, The size of flames from natural fires, 497 (1962) -1--1.
[22] J.M. Forthofer, S.L.J.J.o.C. Goodrick, Review of vortices in wildland fire, 2011 (2011).