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Identifying Characteristics of Wildfire Towers and Troughs
Atmosphere ( IF 2.9 ) Pub Date : 2020-07-28 , DOI: 10.3390/atmos11080796
Tirtha Banerjee , Troy Holland , Kurt Solander , Marlin Holmes , Rodman Linn

Wildfire behavior is dictated by the complex interaction of numerous physical phenomena including dynamic ambient and fire-induced winds, heat transfer, aerodynamic drag on the wind by the fuel and combustion. These phenomena create complex feedback effects between the fire and its surroundings. In this study, we aim to study the mechanisms by which buoyant flame dynamics along with vortical motions and instabilities control wildfire propagation. Specifically, this study employs a suite of simulations conducted with the physics-based coupled fire-atmosphere behavior model (FIRETEC). The simulations are initialized with a fire line and the fires are allowed to propagate on a grass bed, where the fuel heights and wind conditions are varied systematically. Flow variables are extracted to identify the characteristics of the alternating counter-rotational vortices, called towers and troughs, that drive convective heat transfer and fire spread. These vortices have previously been observed in wildfires and laboratory fires, and have also been observed to arise spontaneously in FIRETEC due to the fundamental physics incorporated in the model. However, these past observations have been qualitative in nature and no quantitative studies can be found in the literature which connected these coherent structures fundamental to fire behavior with the constitutive flow variables. To that end, a variety of state variables are examined in the context of these coherent structures under various wind profile and grass height conditions. Identification of various correlated signatures and fire-atmosphere feedbacks in simulations provides a hypothesis that can be tested in future observational or experimental efforts, potentially assisting experimental design, and can aid in the interpretation of data from in situ detectors.

中文翻译:

识别野火塔和槽的特征

野火行为是由众多物理现象的复杂相互作用所决定的,这些物理现象包括动态的环境风和由火引起的风,热传递,燃料和燃烧对风的气动阻力。这些现象会在火灾及其周围环境之间产生复杂的反馈效果。在这项研究中,我们旨在研究浮力火焰动力学以及涡旋运动和不稳定性控制野火传播的机制。具体而言,本研究采用了一套基于物理的耦合火-气行为模型(FIRETEC)进行的模拟。模拟用火线初始化,火被允许在草地上传播,在草地上,燃料高度和风况会系统地变化。提取流量变量以识别交替的反向旋转涡流(称为塔和谷)的特征,这些涡流驱动对流传热和火势蔓延。先前已在野火和实验室火灾中观察到这些涡流,并且由于模型中包含的基本物理原理,也已观察到它们在FIRETEC中自发产生。然而,这些过去的观察本质上是定性的,在文献中找不到定量研究,这些研究将火灾行为基础的这些连贯结构与本构流动变量联系起来。为此,在各种风廓线和草高条件下,在这些相干结构的背景下检查了各种状态变量。
更新日期:2020-07-28
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