Physics-based coupled fire–atmosphere models are based on approximations to the governing equations of fluid dynamics, combustion, and the thermal degradation of solid fuel. They require significantly more computational resources than the most commonly used fire spread models, which are semi-empirical or empirical. However, there are a number of fire behaviour problems, of increasing relevance, that are outside the scope of empirical and semi-empirical models. Examples are wildland–urban interface fires, assessing how well fuel treatments work to reduce the intensity of wildland fires, and investigating the mechanisms and conditions underlying blow-up fires and fire spread through heterogeneous fuels. These problems are not amenable to repeatable full-scale field studies. Suitably validated coupled atmosphere–fire models are one way to address these problems. This paper describes the development of a three-dimensional, fully transient, physics-based computer simulation approach for modelling fire spread through surface fuels. Grassland fires were simulated and compared to findings from Australian experiments. Predictions of the head fire spread rate for a range of ambient wind speeds and ignition line-fire lengths compared favourably to experiments. In addition, two specific experimental cases were simulated in order to evaluate how well the model predicts the development of the entire fire perimeter.

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A physics-based approach to modelling grassland fires

In recent years, advances in computational power and spatial data analysis (GIS, remote sensing, etc) have led to an increase in attempts to model the spread and behaviour of wildland fires across the landscape. This series of review papers endeavours to critically and comprehensively review all types of surface fire spread models developed since 1990. This paper reviews models of a physical or quasi-physical nature. These models are based on the fundamental chemistry and/or physics of combustion and fire spread. Other papers in the series review models of an empirical or quasi-empirical nature, and mathematical analogues and simulation models. Many models are extensions or refinements of models developed before 1990. Where this is the case, these models are also discussed but much less comprehensively.

A review of wildland fire spread modelling, 1990-present, 1: Physical and quasi-physical models

Mathematical models and calculation systems for the study of wildland fire behaviour

In recent years, advances in computational power have led to an increase in attempts to model the behaviour of wildland fires and to simulate their spread across the landscape. The present series of articles endeavours to comprehensively survey and precis all types of surface fire spread models developed during the period 1990–2007, providing a useful starting point for those readers interested in recent modelling activities. The current paper surveys models of a physical or quasi-physical nature. These models are based on the fundamental chemistry and physics, or physics alone, of combustion and fire spread. Other papers in the series review models of an empirical or quasi-empirical nature, and mathematical analogues and simulation models. Many models are extensions or refinements of models developed before 1990. Where this is the case, these models are also discussed but in much less detail.

Wildland surface fire spread modelling, 1990-2007. 1: Physical and quasi-physical models

Modeling the propagation of a wildfire through a Mediterranean shrub using a multiphase formulation

A multiphase formulation for fire propagation in heterogeneous combustible media

The propagation of wind-aided line fires through fuel beds is simulated by using a multiphase approach. In this approach, a gas phase flows through N solid phases which constitute an idealized reproduction of the heterogeneous combustible medium. A set of time-dependent equations is obtained for each phase and the coupling between the gas phase and the solid phases is rendered through exchange terms of mass, momentum, and energy. Turbulence is approached by using a RNG k−e statistical model constructed from the Favre averaging method. The radiative transfer equation extended to multiphase media is solved using the discrete ordinates method (DOM). Soot formation is taken into account for the evaluation of the absorption coefficient of the soot/fuel particles/combustion products mixture using the gray gas assumption. First-order kinetics is incorporated to describe water vaporization, pyrolysis, and char combustion processes. The solution is performed numerically by a finite-volume method including a high-order upwind convective scheme and a flux limiter strategy along with a projection method for the pressure–velocity coupling. This model has been applied to describe the unsteady behavior of wind-aided fires spreading through a litter of dead pine needles and the induced hydrodynamics. The numerical results obtained from our model are presented and compared to measurements and predictions from other laboratory-based models.

Firespread through fuel beds: Modeling of wind-aided fires and induced hydrodynamics

The effects of cross wind on the behaviour of a turbulent diffusion flame have been studied numerically. The multicomponent turbulent reacting flow is approached using a two-equation (κ - ϵ) statistical model constructed from the Favre averaging method. To improve the representation of turbulent fields in fully developed and weak turbulent regions, RNG (Renormalization Group) κ - ϵ turbulence modelling is adopted. Infinitely fast reaction is assumed and the combustion rate is fully determined by the turbulent mixing rate of fuel and oxygen using the Eddy Dissipation Concept (EDC). Energy lost by radiation is taken into account and soot formation is computed for the evaluation of the absorption coefficient of the soot-gas mixture using the gray gas assumption. Calculations have been performed both with and without wind. The numerical results show that the flow is characterized by oscillations which affect significantly the flame behaviour. The development of shear buoyancy-driven instabilities (Kelvin-Helm...

Numerical Simulation of Turbulent Diffusion Flame in Cross Flow

The use of grey assumption to describe the attenuation of thermal radiation in fire/water spray interactions is investigated. The gas phase is assumed to be radiatively non-participating. Radiative fluxes obtained using mean Planck radiative properties are compared with those integrated over all the wavelengths. On a spectral basis, the radiative transfer equation (RTE) is obtained using the Mie absorption and scattering efficiencies, and the Henyey-Greenstein phase function is used to approximate the exact Mie phase function. RTE is solved using the finite-volume method. Results show the capability of the grey model to provide correct results for an optical thickness less than 2. For optically thicker media, an improved model is proposed. It consists in dividing the radiative intensity into three or more spectral bands and using individual mean Planck quantities for each band. Deviations from the reference spectral model results are estimated as well as the gain in computational time for a wide range of ...

On the use of gray assumption for modeling thermal radiation through water sprays

This paper describes a multiphase approach to determining the rate of propagation of a line fire through a randomly packed fuel bed of thermally thin cellulose particles and the induced hydrodynamics inside and above the litter. A set of time-dependent balance equations is solved for each phase (a gas phase andN solid phases) and the coupling between the gas phase and the solid phases is rendered through exchange terms of mass due to thermal degradation of the fuel material (heating, drying, pyrolysis, and char combustion), momentum, and energy. The radiative transfer equation for the fuel bed is deduced from the P1-approximation, and radiation from the flame to the fuel bed is accounted for using the empirical model of Markstein. The kinetics is incorporated to describe pyrolysis and combustion processes. Solution is performed numerically by a finite-volume method. The development of a line fire from the moment of initiation to quasisteady propagation is predicted and discussed. Results obtained by this multiphase model are compared to measurements made on laboratory fires using dead pine needles as fuel. The predicted rates of fire spread for some configurations, including slope effects, agree well with measured values.

J. C. Loraud

Papers

A multiphase formulation for fire propagation in heterogeneous combustible media

Firespread through fuel beds: Modeling of wind-aided fires and induced hydrodynamics

Numerical Simulation of Turbulent Diffusion Flame in Cross Flow

On the use of gray assumption for modeling thermal radiation through water sprays

Wildfire propagation: A two-dimensional multiphase approach