Search

Background: Fire whirls are often reported to occur in wildland fires and can induce serious difficulties in firefighting by abruptly modifying fire behaviour, exposing firefighters and even causing casualties. Aims: The aim of this study was to examine the formation of fire whirls on a windward slope. Methods: Straight and V-shaped heated wires and burners were used to emulate fire spread fronts of various fire intensities. Different slope angles and ambient wind speeds were considered, to observe the formation and behaviour of fire whirls. Key results: A fire whirl appeared over a straight-line fire in the presence of wind, and a couple of counter-rotating fire whirls appeared over the two flanks of a V-shaped line fire. Conclusions: Two interaction regimes were experimentally observed and theoretically explained for the interaction of two fire whirls. We found that an effective wind speed instead of the local wind speed in sloped terrains can quantify the critical condition for the formation of fire whirls over line fires of different burning intensities. Implication: A critical effective wind speed correlation that couples slope angle, burning intensity and radiative fraction of a line fire can predict fire whirl risk in wildland fire fighting. A fire front spreading on a windward slope typically has a V-shape that can induce fire whirls, posing a risk to firefighters. We considered ambient wind, slope angle and line fire characteristics to predict the fire whirl risk. [ABSTRACT FROM AUTHOR]

Wildfires are complex phenomena, both in time and space, in ecosystems. The ability to understand wildfire dynamics and to predict the behaviour of the propagating fire is essential and at the same time a challenging practice. A common approach to investigate and predict such phenomena is making the most of power of numerical models and simulators. Improved and more accurate methods for simulating fire dynamics are indispensable to managing suppression plans and controlled burns, decreasing the fuel load and having a better assessment of wildfire risk mitigation methodologies. This paper is focused on the investigation of existing simulator models applicable in predicting wildfire spread and wind fire interaction. The available software packages are outlined with their broad range of applications in fire dynamic modeling. Significance of each work and associated shortcomings are critically reviewed. Finally, advanced simulations and designs, accurate assumptions, and considerations for improving the numerical simulations, existing knowledge gaps in scientific research and suggestions to achieve more efficient developments in this area are revisited. [ABSTRACT FROM AUTHOR]

Large eddy simulation (LES) based computational fluid dynamics (CFD) simulators have obtained increasing attention in the wildland fire research community, as these tools allow the inclusion of important driving physics. However, due to the complexity of the models, individual aspects must be isolated and tested rigorously to ensure meaningful results. As wind is a driving force that can significantly dictate the behavior of a wildfire, the simulation of wind is studied in the context of a particular LES CFD model, the Wildland-urban interface Fire Dynamics Simulator (WFDS). As WFDS has yet to be tested extensively with regard to wind flow within and above forest canopies, a study of its ability to do so is carried out. First, three simulations are conducted using periodic boundary conditions. Two of these assume a spatially heterogeneous forest and one models wind downstream of a canopy edge. Second, two simulations are conducted with specified 'inflow' conditions using two inflow profiles: one static and one dynamic (driven by a precursor simulation). Using periodic boundary conditions, the model is found to generate profiles of mean velocity and turbulent statistics that are representative of experimental measurements. The dynamic inflow scenario is found to perform better than the static case. Key words: computational fluid dynamics, large eddy simulation, wildland fire, canopy, wind. Les simulateurs de dynamique des fluides numerique (CFD) bases sur la methode de simulation de grands ecoulements tourbillonnants (LES) sont l'objet d'une attention croissante de la part des chercheurs dans le domaine des feux de foret etant donne que ces outils permettent d'inclure des facteurs physiques determinants. Cependant, a cause de la complexite des modeles, des aspects particuliers doivent etre isoles et testes rigoureusement pour s'assurer d'obtenir des resultats significatifs. Etant donne que le vent est un element moteur important qui peut facilement determiner le comportement d'un feu de foret, la simulation du vent est etudiee dans le contexte d'un modele LES CFD particulier : le simulateur de la dynamique des incendies en milieu periurbain. Ce logiciel de simulation doit encore etre teste de facon exhaustive en ce qui concerne l'ecoulement du vent a l'interieur et au-dessus du couvert forestier; sa capacite a cet egard doit par consequent etre etudiee. Premierement, trois simulations sont effectuees en utilisant des conditions aux limites periodiques. Deux de ces simulations assument que la foret est spatialement heterogene et une autre modelise le vent en aval de la lisiere d'un couvert forestier. Deuxiemement, deux simulations sont effectuees dans des conditions d'ecoulement determinees. Des profils d'ecoulement statique et d'ecoulement dynamique (determine par une simulation prealable) sont utilises. Avec l'utilisation de conditions aux limites periodiques, le modele genere des profils de vitesse moyenne et des statistiques de turbulence representatifs des mesures experimentales. On obtient une meilleure performance avec le scenario d'ecoulement dynamique que statique. [Traduit par la Redaction] Mots-cles: dynamique des fluides numerique, simulation de grands ecoulements tourbillonnants, feu de foret, couvert forestier, vent., 1. Introduction Numerical simulation of wildland fire dynamics has shown great potential as a tool, particularly for researchers, as the large range of scales and conditions encountered in wildland fires [...]