Fire Whirls

Abstract

Fire whirls present a powerful intensification of combustion, long studied in the fire research community because of the dangers they present during large urban and wildland fires. However, their destructive power has hidden many features of their formation, growth, and propagation. Therefore, most of what is known about fire whirls comes from scale modeling experiments in the laboratory. Both the methods of formation, which are dominated by wind and geometry, and the inner structure of the whirl, including velocity and temperature fields, have been studied at this scale. Quasi-steady fire whirls directly over a fuel source form the bulk of current experimental knowledge, although many other cases exist in nature. The structure of fire whirls has yet to be reliably measured at large scales; however, scaling laws have been relatively successful in modeling the conditions for formation from small to large scales. This review surveys the state of knowledge concerning the fluid dynamics of fire whirls, including the conditions for their formation, their structure, and the mechanisms that control their unique state. We highlight recent discoveries and survey potential avenues for future research, including using the properties of fire whirls for efficient remediation and energy generation.

Influence of Eddy-Generation Mechanism on the Characteristic of On-Source Fire Whirl

“…In addition, by comparing the results presented in Table 2 with those in Table 1, it can be concluded that the radius determined based on the temperature is generally larger than that based on circulation, which again is in good agreement with the experimental observations [1]. Collectively, the preceding assessment of the axial, radial and tangential velocity demonstrates that, with the additional vorticity induced by the entrainment via the additional slit, the swirling motion within the domain is intensified, and the circulation of the dominant region is elongated.…”

“…Fire whirl is a unique swirling diffusion flame that often occurs in urban and wildland fires with disastrous effects [1]. The whirling combustion flow limits the radial flame dispersion and stretches the hot plume to rise upon an elevated vertical angular path, and as a result significantly increases the burning rate, flame height, and flame temperature and radiation flux to the surroundings [2].…”

The Carr Fire Vortex: A Case of Pyrotornadogenesis?

“…Specifically, the latent heating reinvigorates the updraft aloft (Freitas et al, 2007;Luderer et al, 2006Luderer et al, , 2009Trentmann et al, 2006) and thereby enhances vortex stretching in the underlying column (CR09). In contrast, nontornadic FGVs concentrate vorticity solely by fire processes (Forthofer & Goodrick, 2011, Tohidi et al, 2018hereafter T18). In both tornadic and nontornadic FGVs, the initial source of near-surface rotation can include tilting of boundary layer wind shear (Church et al, 1980), differential heating by the fire (CR09; T18), spatial variations fire processes (Kuwana et al, 2013;Zhou & Wu, 2007), mesoscale to synoptic processes (Seto & Clements, 2011;Umscheid et al, 2006), and flow-topography interactions (Countryman, 1971;Sharples et al, 2015).…”

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

“…In the literature, scaling analyses have often been used to identify parameters and quantities to describe the occurrence of fire whirls [9][10][11][12]. The recent extension of this analysis to blue whirls [7] showed that blue whirls exist in a regime distinct from traditional fire whirls.…”