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Investigation of spotting and intrinsic fire dynamics using a coupled atmosphere-fire modelling framework
Large plume-driven wildfires are among the most destructive and unpredictable of all natural hazards. A prerequisite for the development of the deep convection characteristic of these fires is the existence of a large area of active flaming, also known as deep flaming. There are a number of processes associated with the development of deep flaming; many involve some form of dynamic fire behaviour, in which dramatic changes in fire behaviour can occur with little or no change in ambient conditions. Another important driver of deep flaming is intense spotting and spot-fire coalescence, which itself involves dynamic fire behaviour. It is difficult to model dynamic fire behaviour in a computationally efficient way; it cannot be modelled with existing operational fire-spread models. This thesis is concerned with the modelling of dynamic fire behaviour, and the modelling of ember transport in turbulent plumes. A coupled atmosphere-fire framework is used to model junction fires (the merging of two separate firelines at an acute angle), and the fundamental processes causing the asociated dynamic behaviour are identified. The idea that fireline curvature can act as a proxy for some of the processes underlying dynamic fire behaviour is critically examined, and rejected. A recently-developed simple coupled model, the pyrogenic-potential model, is discussed. It is found to produce results comparable with that of a coupled atmosphere-fire model in simple test cases involving the ignition of fires along circular arcs. The pyrogenic-potential model can capture some forms of dynamic behaviour, and is efficient enough to be used operationally. To study ember transport in turbulent plumes, a large eddy model is used to simulate the plume from a static heat source, and the resulting wind field is used to model the transport of embers under various assumptions. It is shown that the terminal-velocity assumption, in which embers are assumed to always move at their terminal velocity with respect to the wind field, leads to an overestimate of ember-landing densities at medium to long ranges. This has important implications for the stochastic modelling of spot-fire development.
Investigation of spotting and intrinsic fire dynamics using a coupled atmosphere-fire modelling framework
Large plume-driven wildfires are among the most destructive and unpredictable of all natural hazards. A prerequisite for the development of the deep convection characteristic of these fires is the existence of a large area of active flaming, also known as deep flaming. There are a number of processes associated with the development of deep flaming; many involve some form of dynamic fire behaviour, in which dramatic changes in fire behaviour can occur with little or no change in ambient conditions. Another important driver of deep flaming is intense spotting and spot-fire coalescence, which itself involves dynamic fire behaviour. It is difficult to model dynamic fire behaviour in a computationally efficient way; it cannot be modelled with existing operational fire-spread models. This thesis is concerned with the modelling of dynamic fire behaviour, and the modelling of ember transport in turbulent plumes. A coupled atmosphere-fire framework is used to model junction fires (the merging of two separate firelines at an acute angle), and the fundamental processes causing the asociated dynamic behaviour are identified. The idea that fireline curvature can act as a proxy for some of the processes underlying dynamic fire behaviour is critically examined, and rejected. A recently-developed simple coupled model, the pyrogenic-potential model, is discussed. It is found to produce results comparable with that of a coupled atmosphere-fire model in simple test cases involving the ignition of fires along circular arcs. The pyrogenic-potential model can capture some forms of dynamic behaviour, and is efficient enough to be used operationally. To study ember transport in turbulent plumes, a large eddy model is used to simulate the plume from a static heat source, and the resulting wind field is used to model the transport of embers under various assumptions. It is shown that the terminal-velocity assumption, in which embers are assumed to always move at their terminal velocity with respect to the wind field, leads to an overestimate of ember-landing densities at medium to long ranges. This has important implications for the stochastic modelling of spot-fire development.
Investigation of spotting and intrinsic fire dynamics using a coupled atmosphere-fire modelling framework
Thomas, Christopher (author)
2019
Theses
Electronic Resource
English
Mathematical Modelling of The Dynamics of Fire Formations in The Open Atmosphere
| British Library Online Contents | 1996