Aerodynamics and heat exchange between the front of a forest fire and the surface layer of the atmosphere

Гришин, А. М.; Gruzin, A. D.; Gruzina, É. É.

doi:10.1007/bf00911665

Cited by 12 publications

(9 citation statements)

References 5 publications

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“…The inverse of this parameter has also been interpreted as a Froude number (Nelson 1993). Byram (1966) extended the parameter study to the problem of large, intensely burning fires known as mass fires, with studies by Grishin et al (1984) and Clark et al (1996b) developing and applying similar parameters to numerical simulations of fires. The study by Clark et al (1996b) utilized a form of Froude number such that the thermal energy term is proportional to the deviation of potential temperature above the fire from ambient conditions.…”

Section: Scaling Parametersmentioning

confidence: 99%

“…Sensible heat fluxes of 0.8-2 MW m 22 , in combination with the moisture produced during the combustion process, can produce buoyancydriven horizontal and vertical circulations that feed back on the fires via the advection of hot gases and burning material and also through the mixing of air with flames to increase flame temperature and subsequently fire intensity (Jenkins et al 2001). Early numerical modeling studies of plumes above forest fires considered only the gross plume characteristics, the result of which was a broad classification of plume-dominated and wind-driven fires, with weaker (stronger) mean winds and greater (lesser) heat output associated with the former (latter) (Byram 1959;Grishin et al 1984). Plume-dominated fires feature more upright plumes whereas wind-driven fires are associated with plumes strongly tilted downstream.…”

Section: Introductionmentioning

confidence: 99%

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Regimes of Dry Convection above Wildfires: Idealized Numerical Simulations and Dimensional Analysis*

Kiefer

Parker

Charney

2009

Journal of the Atmospheric Sciences

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Wildfires are capable of inducing atmospheric circulations that result predominantly from large temperature anomalies produced by the fire. The fundamental dynamics through which a forest fire and the atmosphere interact to yield different convective regimes is still not well understood. This study uses the Advanced Regional Prediction System (ARPS) model to investigate the impact of the environmental (i.e., far upstream, undisturbed by fire) wind profile on dry convection above a prescribed heat source of an intensity and spatial scale comparable to a wildfire. Dimensional analysis of the fire–atmosphere problem provides two relevant parameters: a surface buoyancy parameter that addresses the amount of heat a parcel of air receives in transiting above the fire and an advection parameter that addresses the degree to which the environmental wind advects updrafts away from the fire. Two-dimensional simulations are performed in which the upstream surface wind speed and mixed layer mean wind speed are varied independently to better understand the fundamental processes governing the organizational mode and updraft strength. The result of these experiments is the identification of two primary classes of dry convection: plume and multicell. Simulated plume cases exhibit weak advection by the mean wind and are subdivided into intense plume and hybrid classes based on the degree of steadiness within the convection column. Hybrid cases contain columns of largely discrete updrafts versus the more continuous updraft column associated with the intense plume mode. Multicell cases develop with strong mixed layer advection and are subdivided into strong and weak classes based on the depth of convection. Intense plume and strong multicell (hybrid and weak multicell) cases occur when the surface buoyancy is large (small). Parcel analyses are performed to more closely examine the forcing of convection within different areas of the parameter space. The multicell (strong and weak) and intense plume modes are forced by a combination of buoyancy and dynamic pressure gradient forcing associated with the perturbation wind field, whereas the hybrid mode is forced by a combination of buoyancy and dynamic pressure gradient forcing associated with the strong background shear. The paper concludes with a discussion of the degree of nonlinearity that is likely to exist at the fire front for each of the convective modes; nonlinear fire behavior is most likely for the hybrid mode and least likely for the weak multicell mode. Knowledge of the sensitivity of the convective mode to upstream conditions can provide information about the degree of nonlinear or erratic fire behavior expected for a given wind profile upstream of the fire.

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Section: Scaling Parametersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Regimes of Dry Convection above Wildfires: Idealized Numerical Simulations and Dimensional Analysis*

Kiefer

Parker

Charney

2009

Journal of the Atmospheric Sciences

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“…Both field and laboratory experiments failed to detect evidence of a fire-wind ahead of the fire-front. On the basis of the above calculations, there seems little reason to expect a firewind in the case of a wind-driven fire, and attempts to impose one have, in the past, led to unrealistic airflow patterns such as those of Nelson (1986: Figure 2) and Grishin et al (1984: Figure 1). The theoretical airflow patterns of these authors are depicted in Figure 2, on which there has also been superimposed a schematic of the results from the wheat stubble burns at Harden.…”

Section: The Fire-windmentioning

confidence: 99%

The interaction of wind and fire

Beer

1991

Boundary-Layer Meteorol

142

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The rate of spread of a wildfire increases markedly when a wind springs up. Why and how this happens is still not completely understood. However, by using a judicious mixture of laboratory experiments, field experiments, sensitivity analyses of existing wildfire spread models and physical reasoning it is possible to identify some features that have not been adequately considered in the past. In particular: (i) the energetics of wind-blown wildfires indicate that a fire-wind may not exist and that the wind may blow through the fire line. ii) The rate of spread of the fire-front depends on the atmospheric stability such that the fire-front speeds are 50% or more faster during winds in the 2 to 6 m/s range under unstable conditions. iii) The wind speed acting on the flame provides an upper limit to the flame propagation speed. Existing attempts to constrain the propagation rate of fire-spread models at high wind speeds appear incorrect and, iv) wind fluctuations interacting with the standing fuel generate sweeps of downward air which carry the flame into the fuel bed and directly preheat the fuel. a

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“…Anomalies of 40-60 K, in combination with the substantial amounts of moisture produced during the combustion process, can produce dramatic buoyancy-driven horizontal and vertical circulations that feed back on the fires via mechanisms, including the advection of hot gases and burning material, and the mixing of air with flames to increase flame temperatures, thereby increasing combustibility (Jenkins et al 2001). Early numerical modeling studies of plumes above forest fires considered only the temporally averaged plume characteristics, the result of which was the classification of "plume-dominated" and "wind-dominated" fires, with weaker (stronger) mean winds and greater (lesser) heat output associated with the former (latter; Byram 1966;Grishin et al 1984). Plume-dominated fires featured more upright plumes while wind-dominated fires were associated with plumes strongly tilted downstream.…”

Section: Introductionmentioning

confidence: 99%

A Study of Two-Dimensional Dry Convective Plume Modes with Variable Critical Level Height

Kiefer

Lin

Charney

2008

Journal of the Atmospheric Sciences

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This study investigates the impact of wind speed and critical level height on dry convection above a prescribed heat source. This is done using the Advanced Regional Prediction System (ARPS) model in its two-dimensional form with an imposed 400-K soil potential temperature perturbation. The result of these experiments is the identification of three modes of convective plumes. The first, termed multicell convective plumes, is analogous to multicell convection generated from squall-line cold pools in the moist atmosphere. The second mode, a deep wave mode, consists of disturbances with wavelengths of 7-10 km and results from the multicell plumes perturbing the dynamically unstable shear flow centered at the critical level. The third mode, termed the intense fire plume, has stronger updrafts than the multicell mode and is marked by quasistationary movement and substantial low-level inflow and upper-level outflow. The presence of a critical level is shown to be crucial to the development of both the deep wave and intense plume modes. The intense fire plume mode is most consistent with the so-called fire storm, or conflagration phenomenon, in which strong updrafts and low-level indrafts can produce mesocyclones and tornadic fire whirls capable of significant damage. This study marks an important step in understanding the dynamics behind the fire storm phenomenon, as well as other types of convection (multicell and deep wave) that may be generated by a fire.

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Aerodynamics and heat exchange between the front of a forest fire and the surface layer of the atmosphere

Cited by 12 publications

References 5 publications

Regimes of Dry Convection above Wildfires: Idealized Numerical Simulations and Dimensional Analysis*

Regimes of Dry Convection above Wildfires: Idealized Numerical Simulations and Dimensional Analysis*

The interaction of wind and fire

A Study of Two-Dimensional Dry Convective Plume Modes with Variable Critical Level Height

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