摘要 :
Numerical simulations using a fire model, FIRETEC, coupled to an atmospheric dynamics model, HIGRAD, are examined to investigate several fundamental aspects of fire behavior in grasslands, and specifically the dependence of this b...
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Numerical simulations using a fire model, FIRETEC, coupled to an atmospheric dynamics model, HIGRAD, are examined to investigate several fundamental aspects of fire behavior in grasslands, and specifically the dependence of this behavior on the ambient atmospheric winds and on the initial length of the fire line. The FIRETEC model is based on a multi-phase transport approach, and incorporates representations of the physical processes that govern wildfires, such as combustion and radiative and convective heat exchange. Results from the coupled model show that the forward spread of the simulated fires increases with increasing ambient wind speed, and the spread rates are consistent with those observed in field experiments of grass fires; however, the forward spread also depends significantly on the initial length of the fire line, and for a given ambient wind speed the spread rate for long (100 m) lines is greater than that for short (16 m) lines. The spread of the simulated fires in the lateral direction also depends on the ambient wind speed and the length of the fire line, and a possible explanation for this effect is given. For weak ambient winds, the shape of the fire perimeter is dramatically different from that seen with higher wind speeds. The shape of the fire perimeter is also shown to depend on the initial length of the fire line. These differences in fire behavior are attributed to the differences in the nature of the coupled atmosphere–fire interactions among these cases, and are described in terms of the complex interplay between radiative and convective heat transfer.
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New physics-based fire behavior models are poised to revolutionize wildland fire planning and training; however, model testing against field conditions remains limited. We tested the ability of QUIC-Fire, a fast-running and comput...
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New physics-based fire behavior models are poised to revolutionize wildland fire planning and training; however, model testing against field conditions remains limited. We tested the ability of QUIC-Fire, a fast-running and computationally inexpensive physics-based fire behavior model to numerically reconstruct a large wildfire that burned in a fire-excluded area within the New York–Philadelphia metropolitan area in 2019. We then used QUIC-Fire as a tool to explore how alternate hypothetical management scenarios, such as prescribed burning, could have affected fire behavior. The results of our reconstruction provide a strong demonstration of how QUIC-Fire can be used to simulate actual wildfire scenarios with the integration of local weather and fuel information, as well as to efficiently explore how fire management can influence fire behavior in specific burn units. Our results illustrate how both reductions of fuel load and specific modification of fuel structure associated with frequent prescribed fire are critical to reducing fire intensity and size. We discuss how simulations such as this can be important in planning and training tools for wildland firefighters, and for avenues of future research and fuel monitoring that can accelerate the incorporation of models like QUIC-Fire into fire management strategies.
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Numerical simulations using a coupled atmosphere-fire model (called HIGRAD/FIRETEC) are examined to investigate the dynamics of fire behavior in grasslands, focusing specifically on the relative roles and contributions of radiativ...
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Numerical simulations using a coupled atmosphere-fire model (called HIGRAD/FIRETEC) are examined to investigate the dynamics of fire behavior in grasslands, focusing specifically on the relative roles and contributions of radiative and convective heat transfer and the relationships of these processes to the evolution of the solid fuel temperature; the three-dimensional velocity fields in the vicinity of the fire; and the depletion of fuel, fuel moisture, and oxygen. The progression of the fire past a given point in these simulations is divided into a preheating period and an active burning period. The preheating period is characterized by a slowly increasing radiative heating of the fuel that evaporates fuel moisture and raises the temperature of the fuel slightly and by weak convective cooling because the gases flowing over the heated solid fuel are still cooler than the fuel itself. The active burning period is characterized by the presence of a strong pulse of convective heating and continued radiative heating, accompanied by the development of large vertical velocities and a rapid increase in fuel temperature that causes the reaction rates to increase and the fuel to begin to burn, producing heat and increasing the rates of depletion of fuel and oxygen. In all simulations, the magnitude of the convective heat transfer is greater than that of the radiative heat transfer; however, these processes and their relationships to the three-dimensional structure and evolution of the fire are shown to depend both on the ambient wind speed and on the specific location along the fire front (e.g., at the head of the fire where the fire is spreading in the direction of the ambient wind, or on the flank of the fire where the fire is spreading in the direction almost perpendicular to the ambient wind).
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Atmospheric forcing and interactions between the fire and atmosphere are primary drivers of wildland fire behavior. The atmosphere is known to be a chaotic system that, although deterministic, is very sensitive to small perturbati...
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Atmospheric forcing and interactions between the fire and atmosphere are primary drivers of wildland fire behavior. The atmosphere is known to be a chaotic system that, although deterministic, is very sensitive to small perturbations to initial conditions. We assume that as a result of the tight coupling between fire and atmosphere; wildland fire behavior, in turn, should also be sensitive to perturbations in atmospheric initial conditions. Observations suggest that low intensity prescribed fire, in particular, is susceptible to small perturbations in the wind field, which can significantly alter fire spread. Here, we employ a computational fluid dynamics model of coupled fire-atmosphere interactions to answer the question: How sensitive is fire behavior to small variations in atmospheric turbulence? We perform ensemble simulations of fires in homogenous grass fuels. The only difference between ensemble members is the state of the turbulent atmosphere provided to the model throughout the simulation. The atmospheric state is a function of the initial conditions applied at the start of the simulation and boundary conditions applied throughout the simulation. We find a wide range of outcomes, with area burned ranging from 2,212 to 11,236 m~2 (>400% change), driven primarily by sensitivity to initial conditions, with nonnegligible contributions from boundary condition variability during the initial 30 s of simulation. Our results highlight the need for ensemble simulations, especially when considering fire behavior in marginal burning conditions.
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A simple, easy-to-evaluate, surrogate model was developed for predicting the particle emission source term in wildfire simulations. In creating this model, we conceptualized wildfire as a series of flamelets, and using this concep...
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A simple, easy-to-evaluate, surrogate model was developed for predicting the particle emission source term in wildfire simulations. In creating this model, we conceptualized wildfire as a series of flamelets, and using this concept of flamelets, we developed a one-dimensional model to represent the structure of these flamelets which then could be used to simulate the evolution of a single flamelet. A previously developed soot model was executed within this flamelet simulation which could produce a particle size distribution. Executing this flamelet simulation 1200 times with varying conditions created a data set of emitted particle size distributions to which simple rational equations could be tuned to predict a particle emission factor, mean particle size, and standard deviation of particle sizes. These surrogate models (the rational equation) were implemented into a reduced-order fire spread model, QUIC-Fire. Using QUIC-Fire, an ensemble of simulations were executed for grassland fires, southeast U.S. conifer forests, and western mountain conifer forests. Resulting emission factors from this ensemble were compared against field data for these fire classes with promising results. Also shown is a predicted averaged resulting particle size distribution with the bulk of particles produced to be on the order of 1 μm in size.
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The structure and dynamics of buoyant plumes arising from surface-based heat sources in a vertically sheared ambient atmospheric flow are examined via simulations of a three-dimensional, compressible numerical model. Simple circul...
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The structure and dynamics of buoyant plumes arising from surface-based heat sources in a vertically sheared ambient atmospheric flow are examined via simulations of a three-dimensional, compressible numerical model. Simple circular heat sources and asymmetric elliptical ring heat sources that are representative of wildland fires of moderate intensity are considered, Several different coherent vortical structures that dominate the plume structure and evolution are evident in the simulations, and these structures correspond well with those observed in plumes from wildland fires For the circular source, these structures include: (i) a counter-rotating vortex pair aligned with the plume trajectory that is associated with a bifurcation of the plume, (ii) transverse shear-layer vortices on the upstream face of the plume, and (iii) vertically oriented wake vortices that form periodically with alternating sign on either side of the downstream edge of the plume base. For the elliptical ring source, a streamwise counter-rotating vortex pair is apparent on each flank, and a transverse horizontal vortex is observed above the head of the source. In all simulations the plume cross section is represented poorly by a self-similar Gaussian distribution.
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Wildfire - that is the unmanaged, uncontrolled burning of forests, brushlands, or grasslands with or without the presence of structures - is an increasing threat to society. We briefly review the extent of this threat, particularl...
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Wildfire - that is the unmanaged, uncontrolled burning of forests, brushlands, or grasslands with or without the presence of structures - is an increasing threat to society. We briefly review the extent of this threat, particularly its relationship to changes in the systems it threatens, and discuss its management. Recent developments in computer models of wildfire are reviewed and their application to several aspects of the wildfire threat are proposed in the context of a national resource. The requirements of n operational wildfire prediction center are discussed as a method to leverage existing and near-term capabilities into new tools to help mitigate the potential threat of this natural process.
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Interest in prescribed fire science has grown over the past few decades due to the increasing application of prescribed fire by managers to mitigate wildfire hazards, restore biodiversity, and improve ecosystem resilience. Numerou...
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Interest in prescribed fire science has grown over the past few decades due to the increasing application of prescribed fire by managers to mitigate wildfire hazards, restore biodiversity, and improve ecosystem resilience. Numerous ecological disciplines use prescribed fire experiments to provide land managers with evidence-based information to support prescribed fire management. Documenting variation in the context and conditions during prescribed fire experimental treatments is critical for management inference, but inconsistencies in reporting critical experimental details can complicate interpretation. Such details are needed to provide ecological and empirical context for data, facilitate experimental replication, enable meta-analyses, and maximize utility for other scientists and practitioners. To evaluate reporting quality in the recent literature, we reviewed 219 prescribed fire experiments from 16 countries published in 11 refereed journals over the last 5 years. Our results suggest substantial shortcomings in the reporting of critical data that compromise the utility of this research. Few studies had specific information on burning conditions such as fuel moisture (22%), quantitative fuel loads (36%), fire weather (53%), and fire behavior (30%). Further, our analysis revealed that 63% of the studies provided precise coordinates for their study area, while 30% of studies indicated the prescribed fire date. Only 54% of the studies provided descriptions of the ignition characteristics. Given these common deficiencies, we suggest minimum reporting standards for future prescribed fire experiments. These standards could be applied to journal author guidelines, directed to researchers and reviewers by the editor, and promoted in the education of fire ecologists. Establishing reporting standards will increase the quality, applicability, and reproducibility of prescribed fire science, facilitate future research syntheses, and foster actionable science.
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Forest fuel management in the context of fire prevention generally induces heterogeneous spatial patterns of vegetation. However, the impact of the canopy structure on both wind flows and fire behavior is not well understood.
摘要 :
A simple, easy-to-evaluate, surrogate model was developed for predicting the particle emission source term in wildfire simulations. In creating this model, we conceptualized wildfire as a series of flamelets, and using this concep...
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A simple, easy-to-evaluate, surrogate model was developed for predicting the particle emission source term in wildfire simulations. In creating this model, we conceptualized wildfire as a series of flamelets, and using this concept of flamelets, we developed a one-dimensional model to represent the structure of these flamelets which then could be used to simulate the evolution of a single flamelet. A previously developed soot model was executed within this flamelet simulation which could produce a particle size distribution. Executing this flamelet simulation 1200 times with varying conditions created a data set of emitted particle size distributions to which simple rational equations could be tuned to predict a particle emission factor, mean particle size, and standard deviation of particle sizes. These surrogate models (the rational equation) were implemented into a reduced-order fire spread model, QUIC-Fire. Using QUIC-Fire, an ensemble of simulations were executed for grassland fires, southeast U.S. conifer forests, and western mountain conifer forests. Resulting emission factors from this ensemble were compared against field data for these fire classes with promising results. Also shown is a predicted averaged resulting particle size distribution with the bulk of particles produced to be on the order of 1 μm in size.
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