The analysis of laboratory fire experiments led to the development of a
reaction-diffusion model for the spread of fire across a fuel bed in windless
and slopeless conditions. A method for the determination of coefficients in
this model based on the dynamic features of a spreading fire is given. The
numerical study of the mathematical problem proposed allows us to predict the
rate of spread, the fire front perimeter and the temperature distribution for
line-ignition and point-ignition fires. These results are compared with
success to experimental data. Furthermore, the model allows us to estimate the
acceleration of spread for a point-ignition fire in its initial stage and in
the steady-state phase.
Une analyse menée sur des expériences de laboratoires nous a
permis de proposer un modèle de réaction-diffussion pour la
propagation du feu sans vent et sans pente au travers d’une
litière. Une méthode d’identification des coefficients du
modèle, à partir des caractéristiques dynamiques de la
propagation du feu, est donnée. L’étude numérique
du problème mathématique nous permet de prédire la
vitesse de propagation, le périmètre du front de feu et la
température dans le domaine d’étude pour des allumages en
ligne et pour des allumages ponctuels. Ces résultats sont
comparés avec succés à des données
expérimentales. De plus, nous sommes aussi en mesure de décrire
l’accélération du front de feu dans les premiers instants
suivant un allumage ponctuel.
Although the modelling of the spreading of a forest fire has made considerable progress recently, there remains a lack of reliable field measurements of thermodynamic quantities. We propose in this paper a method and a set of measuring structures built in order to improve the knowledge on the fundamental physical mechanisms that control the propagation of wildland fires. These experimental apparatus are designed to determine: the fire front shape, its rate of spread, the amount of energy impinging ahead of it, the vertical distribution of the temperature within the fire plume as well as the wind velocity and direction. The methodology proposed was applied to a fire spreading across the Corsican scrub on a test site.The recorded data allowed us to reconstruct the fire behaviour and provide its main properties. Wind and vegetation effects on fire behaviour were particularly addressed.
This work presents a new modelling approach to the elaboration of a simple model of surface fire spread. This model runs faster than real-time and will be integrated in management tools. Until now, models used in such tools have been based on an empirical relationship. These tools may be efficient for conditions that are comparable to those of test-fires but the absence of a physical description makes them inapplicable to other situations. This paper proposes a physical 3D model of surface fire able to predict fire behaviour faster than real-time. This model is tested on experiments carried out across fuel beds under slope and wind conditions.
Simulating the interaction between fire and atmosphere is critical to the estimation of the rate of spread of the fire. Wildfire's convection (i.e., entire plume) can modify the local meteorology throughout the atmospheric boundary layer and consequently affect the fire propagation speed and behaviour. In this study, we use for the first time the Méso-NH meso-scale numerical model coupled to the point functional ForeFire simplified physical front-tracking wildfire model to investigate the differences introduced by the atmospheric feedback in propagation speed and behaviour. Both numerical models have been developed as research tools for operational models and are currently used to forecast localized extreme events. These models have been selected because they can be run coupled and support decisions in wildfire management in France and Europe. The main originalities of this combination reside in the fact that Méso-NH is run in a Large Eddy Simulation (LES) configuration and that the rate of spread model used in ForeFire provides a physical formulation to take into account the effect of wind and slope. Simulations of typical experimental configurations show that the numerical atmospheric model is able to reproduce plausible convective effects of the heat produced by the fire. Numerical results are comparable to estimated values for fire-induced winds and present behaviour similar to other existing numerical approaches.
A two-dimensional non-stationary model of a fire spreading across a bed of fuel is proposed incorporating the effects of wind and slope. The contributions of both radiative and convective preheating ahead of the fire-front are included. The radiation impinging on the top of the fuel-bed is determined, assuming the flame is a radiant surface. Convective heat transfer in the fuel layer is considered using a simplified description of the flow through the bed of fuel. Dedicated laboratory-scale experiments have been carried out across beds of pine needles for horizontal fire spread in still air, in order to validate the model. Experiments conducted under wind and slope conditions are also considered. Model predictions are then compared to these experimental measurements.
This paper is devoted to the improvement of semi-physical fire spread models. In order to improve them, a theoretical approach based on the multiphase concept was carried out. The multiphase approach which considers the finest physical phenomena involved in fire behaviour was reduced by making several assumptions. This work led us to a simplified set of equations, Among these. a single equation for the thermal balance was obtained by using the thermal equilibrium hypothesis. This approach has been applied to the improvement of our semi-physical model in order to take into account increasing wind influence. The predictions of the improved model were then compared to experimental data obtained for fire spread conducted across pine needle fuel beds. To this end, different slope values and varying wind velocities were considered. The experimental tendency for the variation of the rate of spread was predicted, Indeed. it increases with increasing wind velocity for a given slope as well as for a given wind with increasing slope.
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