Effect of Wind on Fire Whirl Over a Line Fire
TL;DR: In this article, the authors present an experimental study on the fire whirls over a line fire with cross wind, focusing on the occurrence frequency of fire whirs, and propose a scaling law for the critical wind speed inducing fire whirs based on the experimental data in this work and literature.
Abstract: Fire whirls are often reported to occur in wildland and urban fires due to the effect of ambient wind. This paper presents an experimental study on the fire whirls over a line fire with cross wind, focusing on the occurrence frequency of fire whirls. The experimental observations indicated that the fire whirls induced by a line fire may spread beyond the line fire region with the effect of wind. For the effect of cross wind, it is indicated that the cross wind basically increases the occurrence frequency, while the velocity components parallel or perpendicular to the line fire have competitive effects. A scaling law is presented for the critical wind speed inducing fire whirls based on the experimental data in this work and literature. A method is proposed to estimate the magnitude of the fire whirl height under the critical wind speed.
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01 Jan 2021
TL;DR: In this paper, the authors present an overall pattern of the essential factors that lead an initial small-scale spreading flame to a large-scale wildfire beyond control, including the complicated transformation of fuel preheating mechanisms, varied large-size flame fronts and unique spread modes induced in specific fire environments.
Abstract: A fact often overlooked is that large-scale wildfires, although occurring infrequently, are responsible for the overwhelming majority of fire-related suppression costs, economic losses, and natural resources damages. Fortunately, the increasingly severe problems of large-scale wildfires worldwide have been receiving ever-growing academic attention. The high-intensity burning behaviors in wildfires stem from the significant interaction of combustion with heat transfer and atmospheric flow under complicated fuel, meteorology, and topography conditions. Therefore, mitigating measures against large-scale wildfire disasters have grown into a challenging research focus for combustion scientists. Research over the past century has resulted in incrementally enhanced insights into the mechanisms of combustion dynamics underlying the various erratic behaviors in large-scale wildfires, with theories and models of fire accelerations developed and validated. These advances are expected to improve the efficacy of large-scale wildfire predictions significantly. Nevertheless, the physical interpretation of the acceleration of large-scale wildfires is far from adequate and complete. This paper intends not to make a comprehensive review of the entire wildfire research field, but to depict an overall pattern of the essential factors that lead an initial small-scale spreading flame to a large-scale wildfire beyond control. It is outlined that the complicated transformation of fuel preheating mechanisms determines the growth of surface fire spread, while varied large-size flame fronts and unique spread modes induced in specific fire environments play an essential role in fire spread acceleration. Additionally, multiple fires burning and merging often act as crucial steps for accelerating surface fire spread, generating large-size flames, and triggering unique spread modes. These major potential factors strike the energy balance of a low-intensity wildfire and push it to a high-intensity state. Several issues regarding intensely burning behaviors in large-scale wildfires are selected for in-depth discussions, for which an overview of the progress and challenges in research is presented. It is concluded that the fundamental exploration targeted at developing application tools capable of dealing with large-scale wildfires remains at its early stages. Opportunities for innovation are abundant, yet systematic and long-term research programs are required.
34 citations
TL;DR: In this paper, the authors describe the historical and most current instances of wind and fire coupled modelling, referred to as simple models, in situ measurements, wind tunnel experiments or numerical studies with CFD.
Abstract: Wind and fire phenomena can together be a devastating force, whether in the case of a building fire, release of smoke in an urban area or forest fire near an urban habitat. Most of the fire phenomena are influenced by the wind, usually for the worse. If we want to understand fires, we have to understand wind as well, and model it appropriately. This modelling is described by the discipline of Computational Wind Engineering, from which we are able to transfer invaluable knowledge to coupled wind-fire analyses. This two-part review is dedicated to such a transfer. In Part I, the authors describe the historical and most current instances of wind and fire coupled modelling, referred to as simple models, in situ measurements, wind tunnel experiments or numerical studies with CFD. The review is subdivided into six categories, namely flame behaviour in wind conditions, indoor flows, natural smoke ventilators, tunnel ventilation, wildfires and firebrand transport, and urban dispersion of smoke. Besides flame behaviour, all remaining topics are covered, to the best of the authors’ knowledge, with multiple references to valuable experimental and numerical studies. In Part II of the review, the authors describe the best practices of Computational Wind Engineering, that may be transferred to fire-oriented numerical studies. This part provides good practice guidelines, reference studies and a proposal for the optimisation of the simulation procedure for coupled wind and fire models.
25 citations
06 Aug 2021
TL;DR: In this paper, a review of the available experimental techniques and numerical simulations used in analyzing fire whirls has been presented in detail, including empirical arrangements including empirical set ups and employed fuels.
Abstract: Fire whirls are a particular case of flame behaviour characterized by a rotating column of fire driven by intense convective heating of air close to the ground. They typically result in a substantial increase in burning rate, temperature, and flame height. Fire whirls can occur in any intense flame environment, including urban areas, particularly within combustible structures, and in wildland or forest fires. Recently, investigations on the creation of fire whirls have attracted much attention. However, most analyses are focused on fire whirl structure, formation, and controlling their unique state. In effect, revisiting the available experimental techniques and numerical simulations used in analyzing fire whirls has received less attention. In this paper, experimental arrangements including empirical set ups and employed fuels are presented in detail. Subsequently, major research progress focused on experimental studies and their laboratory setup is fully discussed, followed by the available numerical simulations, including combustion and turbulence models. Applied methodologies and chosen software in the recent numerical studies are also reviewed exclusively. Finally, the latest findings are featured, and prospective pathways are advised.
10 citations
TL;DR: In this article, the authors studied fire whirls formed behind an L-shaped wall in a crossflow and found that there was a narrow range of crossflow velocity that led to the formation of an intense and stable fire whir.
9 citations
TL;DR: In this paper, the authors used high-speed video recording tools during the experiments, as well as the system of multiphase media diagnostics based on panoramic optical flow visualization techniques.
Abstract: Paper presents the experimental results about fire extinction in the model fire sites of forest combustible materials. We use the high-speed video recording tools during the experiments, as well as the system of multiphase media diagnostics based on panoramic optical flow visualization techniques. The presented experiments prove that it is possible to extinguish the forest combustible material (FCM) by small amount of water. The study considers several ways to stop FCM thermal decomposition: by individual large water droplets (1–3 mm), by an aerosol flow (the droplet size is from 0.05 mm to 0.12 mm), or through water film formation on the FCM surface. Typical durations of the FCM thermal decomposition and time of fire suppression are determined for various conditions of interaction with water. The experimental results identify which amount of water is enough to extinguish the FCM by different ways of water transfer to the reacting surface layer. Furthermore, it is estimated how the component composition and the properties of the tested FCM mixtures effects onto the characteristics of the investigated processes. The residual fraction of the FCM was evaluated by comparison of initial and final (after extinguishing) mass of the sample.
8 citations
Cites background from "Effect of Wind on Fire Whirl Over a..."
...The references [12] make it clear that wind effect is an independent and very complicated problem at the investigations of issues of the extinguishing processes optimization....
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References
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TL;DR: In this paper, the authors measured the flame length, velocity, temperature, and mass flux for line fires in a very similar manner to axisymmetric systems and found that the air entrainment coefficient for non-reacting, buoyant plume region in the Boussinesq approximation and assuming Gaussian distributions for horizontal velocity and temperature is 0.13.
113 citations
TL;DR: In this article, three types of scale-models, with scaling ratios of 1 235, 1 2500, and 1 4837, corresponding to three actual fire whirls (prototypes) were designed in the laboratory.
112 citations
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TL;DR: In this article, a scaling law that predicts the critical lateral wind velocity was developed and validated by various data including scale-model experiments by other researchers and real urban fire whirls, and a dimensional analysis was conducted to understand the effect of flow circulation on the increase in flame height.
95 citations
01 Jan 2007
TL;DR: In this article, an experimental and methodological investigation on the behaviors of square fire arrays which are composed of 3.5 to 7.7 n-heptane fires initiated from fuel pans of 5 cm in diameter and 2 cm in height is presented.
Abstract: This paper gives an experimental and methodological investigation on the behaviors of square fire arrays which are composed of 3 × 3 to 7 × 7 n-heptane fires initiated from fuel pans of 5 cm in diameter and 2 cm in height. It is intended to develop a burn-out time (BOT) data analysis method to analyze the interaction effects (which may induce fire merging and fire whirls) among the multiple fires. In 26 fire tests the fire point spacing D varied from 20 to 50 cm for each array size and in several cases shear flow was added from one side of the array. By considering the flame height L a reasonable critical condition for initiation of fire merging was implied to be D/L = 0.29 − 0.34, which is independent of the fire array size and fire point spacing. By burn-out time data the Interaction index I (m) and Interaction link index A (m, n) were defined to characterize the fire interactions. The assumptions essential to solve the equation system of I (m) = ∑n A (n, m) were examined in detail, whereby the equation system was solved. The analysis showed that the burn-out time data analysis realizes a quantitatively reasonable comparison of the fire interaction effects, thus indicating that it is reasonable to regard the burn-out time as a measure for the average burning rate for each specific fire point. An apparent criterion of BOT(m)/BOTR = 0.5 was summarized to identify whether any fire point m will be completely involved in fire merging (where BOTR is the burn-out time of the free burning reference fire point). It was implied that the interaction effect imposed on any fire is mainly ascribed to its adjacent four fires. The effects of shear flow to fire burning and occurrences of fire whirls were also discussed.
88 citations
TL;DR: In this paper, the effects of slope (0°, 10°, 20°, 30°) and fuel bed width (1, 2, 3 m) on fire behavior variables such as rate of spread, fuel consumption, flame residence time, temperatures and flame geometry are also reported.
Abstract: A set of 109 laboratory fires in Pinus halepensis fuel beds (1 kg m–2) was used to test the effects of slope (0°, 10°, 20°, 30°) and fuel bed width (1, 2, 3 m) on fire behaviour variables such as rate of spread, fuel consumption, flame residence time, temperatures and flame geometry. The qualitative behaviour of the fires is also reported. The 20° and 30° upslope fires are pointed in shape and fire whirls moving along the fire flanks in the direction of the fire head are systematically observed in 30° upslope fires. Flame residence time increases with increasing slope angle, and both slope angle and fuel bed width affect rate of spread. The slope effects observed in 10° and 20° slope angles and in the narrowest fuel beds (1 and 2 m) are similar to those predicted by operational models. However, the observed slope effect at the 30° slope angle is underestimated by these models, in particular in 3 m-wide fuel beds. Flame temperatures correlate closely with dimensionless height and flame lengths correlate closely with fire line intensity. Mechanisms that could explain the different effects observed are suggested and discussed.
81 citations