CAREER: Understanding the Mechanisms of Wildland Fire Spread

根据CBET-1554026，Gollner大野火对当地人口和自然资源构成巨大威胁，并向大气排放碳和颗粒物。消防员、社区规划者和当地居民都依赖于对野火蔓延的准确预测，以进行作战灭火、疏散、社区设计和规定的火灾设计。在野火界，众所周知，风力或坡度的增加会增加野火的蔓延速度；然而，火蔓延的物理机制并不是很清楚。这种不确定性在一定程度上解释了为什么没有任何模型能够准确预测火灾蔓延的临界门槛。重要的阈值包括火灾将何时扑灭或从地面火势蔓延到树顶的过渡。这项研究项目将利用实验室实验开发定量模型来描述火灾蔓延的物理过程。一旦这些改进的火灾蔓延模型被开发出来，它们就可以用于预测火灾扑救、疏散和火灾天气警报。解决野火问题需要的不仅仅是高级研究。还需要一支训练有素的工作人员，了解野地火灾中的实际和科学火灾问题。在这一项目的同时，还将实施两个外联方案。首先，一个针对初中和高中女生的教育项目将使用火灾科学作为一种独特的途径，向未被充分代表的学生介绍STEM职业。其次，研究人员将与第一批响应人员--荒野消防员--合作，向他们通报危险和安全技术。这一建议的研究目的是了解由反应流不稳定性驱动的间歇加热对野火蔓延的作用，希望这一知识可能会导致野火蔓延的可测试的物理理论。目前的模型要么依赖于实验结果，要么假设辐射是主要的热传递机制。PI和他的合作者最近的观察表明，在许多情况下，火焰的间歇性加热是推动火焰传播的同样重要的过程，不能被忽视。源于野地大火反应性流动的浮力不稳定将火焰喷射到远处的未点燃的燃料中，推动了蔓延。在最具破坏性的野火中，这些制度往往占主导地位，因此，当前的火焰传播模型失败了。这项对间歇燃料加热的研究将有助于这些重要的数值工具，这些工具将解决极端火灾条件下的严重故障。实验工作将包括在强制流动、倾斜和组合结构下使用固定式燃烧器。此外，还将使用脉冲气体燃烧器来耦合火焰不稳定性对细燃料点火的影响，从而驱动火焰传播。理论工作将包括开发理论模型和标度关系，以研究流动中相干结构的形成及其对细燃料间歇加热的影响。新模型的开发和与美国林业局的合作将把这些成果直接推向实践，并将荒野火灾和燃烧科学的不同领域结合在一起。

CBET-1554026, GollnerLarge wildland fires pose an enormous threat to local populations and natural resources, and contribute carbon and particulate emissions to the atmosphere. Firefighters, community planners, and local residents all depend on accurate predictions of the spread of wildland fires for operational firefighting, evacuations, community design, and prescribed fire design. It is well known in the wildland fire community that increasing winds or slope will increase the rate of spread of a wildfire; however, the physical mechanisms by which a fire spreads are not well known. This uncertainty is, in part, why no models can accurately predict the critical thresholds for fire spread. Important thresholds include when a fire will extinguish or transition from surface fire spread to crowning through the tree-tops. This research project will utilize laboratory experiments to develop quantitative models to describe the physics of fire spread. Once these improved models for fire spread are developed, they can be used for predicting fire suppression, evacuations, and fire weather alerts. Solving the wildfire problem will take more than just advanced research. A workforce trained to understand both the practical and scientific fire problems in wildland fire will also be necessary. In conjunction with this project, two outreach programs will be implemented. First, an educational program for middle and high school girls will use fire science as a unique avenue to introduce underrepresented students to STEM careers. Second, researchers will work with the first responders - wildland firefighters, to inform them of hazards and safety techniques. The research objective of this proposal is to understand the previously-unexplored role of intermittent heating that is driven by reacting-flow instabilities on wildland fire spread, in the hope that this knowledge may lead to a testable, physical theory of wildland fire spread. Current models either rely on empirical results or assume that radiation is the dominant heat transport mechanism. Recent observations by the PI and his collaborators have instead shown that intermittent heating from flames is, in many regimes, an equally important process driving flame spread and cannot be neglected. Buoyant instabilities originating in the reacting flow of wildland fires eject flames far ahead into unignited fuel, driving the spread. During the most devastating wildfires, these regimes tend to be dominant and, hence, current flame spread models fail. This study of intermittent fuel heating will contribute to these important numerical tools which will address critical failures during extreme fire conditions. Experimental work will include the use of stationary burners under forced-flow, inclined, and combined configurations. In addition, a pulsed-gas burner will be used to couple the effects of flame instabilities on fine fuel ignition which drive flame spread. Theoretical work will include developing theoretical models and scaling relationships for the formation of coherent structures in the flow and their effects on intermittent heating of fine fuels. The development of new models and collaboration with the U.S. Forest Service will propel these results directly into practice and couple the disparate fields of wildland fire and combustion science.