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Dynamics of shrub fires investigated via physics based modeling.

机译:通过基于物理的建模研究灌木丛火灾的动力学。

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摘要

A physics based model, capable of predicting fire spread through a multiphase porous media, is formulated and described in detail. The resulting governing equations of fluid dynamics, combustion, heat transfer and thermal degradation of solid fuel, are solved using discrete numerical methods. The burning of an isolated chamise (Adenostoma fasciculatum ) shrub approximately 1 m in height, similar to previously reported experimental study, was investigated using this physics based model. Global quantities including burning time, total mass consumed, time history of mass loss rate and time to reach maximum mass loss rate are found to be in good agreement with experimental results. The model is then used to explore the importance of distribution of solid fuel bulk density, fuel moisture content, thermophoresis of soot particles and flame merging on the dynamical behavior of shrub fires in quiescent atmosphere.;Results from burning of an isolated shrub indicate that the local vertical fire spread rate within the shrub increases when the shrub bulk density is distributed along its height, the distribution being consistent with field measurements, as compared to that seen in a uniform bulk density shrub. Time required to initiate the burning of shrub and the amount of mass left unburnt increased by almost a factor of 1.5 and 10, respectively, when shrub moisture content is increased from 20% to 100%. With a two fold increase in moisture content, from 40% to 80%, the fire spread rate in vertical direction is seen to reduce by a factor 0.7. Soot thermophoretic velocities are found to be negligible compared to their convective counterparts. For this reason, global predictions of fire remained unaffected even if thermophoretic transport of soot was neglected.;Fire-fire interactions are investigated by considering two different shrub arrangements; (1) two shrubs placed adjacent to each other (two-shrub); and (2) three shrubs located on the vertices of an equilateral triangle (three-shrub). All shrubs are ignited simultaneously with the aid of separate ground fuels. The peak mass loss rate and the vertical fire spread rate within a shrub decreases with an increasing shrub separation distance. At zero separation distance, heat release rate, normalized by number of shrubs, is enhanced by 5% and 15%, for the two-shrub and the three-shrub arrangement, respectively. Generation of strong vorticity, due to higher magnitudes of gravitational torque, appears to be the cause for enhanced burning in the three-shrub arrangement. This phenomena is seen to be much weaker for the two-shrub arrangement. Interactions between the individual fires cease to exist for a center-to-center distance of 1.5 and 2 times the shrub diameter for the two-shrub and the three-shrub arrangement, respectively.
机译:制定并详细描述了基于物理的模型,该模型能够预测通过多相多孔介质传播的火势。使用离散数值方法求解了所得的流体动力学,燃烧,传热和固体燃料热降解的控制方程。使用这种基于物理的模型,研究了燃烧大约1 m高的孤立的灌木(Adenostoma fasciculatum)灌木的燃烧,类似于先前报道的实验研究。发现包括燃烧时间,消耗的总质量,质量损失率的时间历史和达到最大质量损失率的时间在内的全球数量与实验结果高度吻合。然后,该模型用于探讨静态燃料堆密度,燃料水分含量,烟灰颗粒的热泳和火焰合并对静止状态下灌木丛火灾动态行为的重要性。;孤立灌木丛的燃烧结果表明,当灌木堆密度沿其高度分布时,灌木内局部垂直火势蔓延率增加,与均匀堆密度灌木中的分布相比,该分布与实地测量一致。当灌木的水分含量从20%增加到100%时,开始燃烧灌木所需的时间和未燃烧的物质的量分别增加了将近1.5倍和10倍。随着水分含量从40%增至80%的2倍,垂直方向的火焰蔓延率降低了0.7倍。与对流对流相比,烟灰的热泳速度被忽略不计。因此,即使忽略了烟尘的热泳传输,全球对火的预测也不会受到影响。 (1)两个相邻放置的灌木丛(两个灌木丛); (2)位于等边三角形顶点的三个灌木丛(三个灌木丛)。在单独的地面燃料的帮助下,所有灌木丛同时被点燃。灌木丛中的峰值质量损失率和垂直火势蔓延率随着灌木丛分离距离的增加而降低。在零分离距离下,对于两种灌木和三种灌木,按灌木数量归一化的放热率分别提高了5%和15%。由于较高的重力转矩,产生强烈的涡旋似乎是三灌木丛布置中燃烧增强的原因。对于两灌木丛布置,该现象被认为要弱得多。在两灌木丛和三灌木丛布置的中心距1.5和2倍灌木直径的中心距中,个体火灾之间的相互作用不再存在。

著录项

  • 作者

    Dahale, Ambarish.;

  • 作者单位

    The University of Alabama in Huntsville.;

  • 授予单位 The University of Alabama in Huntsville.;
  • 学科 Engineering Mechanical.;Engineering Chemical.
  • 学位 Ph.D.
  • 年度 2014
  • 页码 193 p.
  • 总页数 193
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 TS97-4;
  • 关键词

  • 入库时间 2022-08-17 11:54:03

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