CAREER: Multiscale Firebrand Transport in the Turbulent Boundary Layer for Fire Science Advancement

野火在美国和世界各地都很常见。当野火蔓延到社区时，野火的成本被放大;通常被称为荒地-城市界面（WUI）。在野火中，燃烧材料的碎片，被称为燃烧物（或飞行余烬），可以在主火前几米到几公里的地方产生、升起并被风携带，并产生几个新的点火。火灾后的研究表明，火把是负责最快的传播和WUIs点燃的主要原因。从火箭升空的那一刻起，纵火犯的轨迹，以及它的着陆点，就取决于湍流的特性。虽然湍流风的结构是由机械力和浮力决定的，但目前对这些因素如何影响斑点风险没有明确的基本认识。此外，目前还不清楚湍流的小涡流在确定火焰行为中起什么作用，因为它们的影响在大多数基于物理学的研究中被忽略了。该项目的主要目的是推进湍流风中火焰传播现象的流体动力学理解，提高公众对消防安全的科学素养，并激励广大学生参与这一新兴领域。该研究将推进火灾蔓延到野火多发地区的预测和缓解，并提高火灾科学在国家景观中的重要性。该研究将使用大涡模拟，拉格朗日粒子跟踪余烬，和表面能量平衡分析，系统地调查湍流尺度相互作用对燃烧物输送的影响，并为火灾科学的进步发现风险。该项目将首次开发和验证一个通用的多尺度计算模型，该模型结合了小尺度湍流的重要影响（即，的大小的顺序）上不断发展的火把; B）研究由于不均匀的时空变化浮力引起的热驱动湍流风对火焰传播的影响，（三）探索机械化的影响--该奖项反映了美国国家科学基金会的法定使命，并被认为是值得通过使用基金会的知识产权评估的支持。优点和更广泛的影响审查标准。

Wildfires have become a common occurrence in the U.S. and around the world. The costs of wildfires are magnified when they spread into communities; commonly referred to as wildland-urban interfaces (WUI). In wildfires, fragments of burning materials, known as firebrands (or flying embers) can be generated, lofted, and carried by the wind several meters to kilometers ahead of the main fire-front and create several new spot fires. Post-fire studies indicated that firebrands are responsible for the fastest spread and the major cause of the ignitions in WUIs. From the moment an ember becomes airborne, a firebrand’s trajectory, and thus its landing spot, depends on characteristics of the turbulent wind flow. While the structure of the turbulent winds is determined by mechanical and buoyant forces, there is currently no clear fundamental understanding of how these factors affect the spotting risks. In addition, it is not clear what role the small eddies of the turbulent flow play in determining firebrand behavior because their effects are neglected in the majority of physics-based studies. The principle aim of this project is to advance fluid-dynamic understanding of the firebrand transport phenomenon in turbulent winds, increase the general public’s scientific literacy about fire safety, and motivate a wide spectrum of students to engage in this emerging field. This research will advance the prediction and mitigation of fire spread into wildfire-prone areas and elevate the importance of fire science in the national landscape.The research will use Large-Eddy Simulations, Lagrangian particle tracking of the embers, and surface energy balance analyses to systematically investigate the effect of the turbulent scale interactions on firebrand transport and spotting risk for the advancement of fire science. The project will, for the first time, a) develop and validate a versatile multiscale computational model of firebrand transport that incorporates the important effects of small scale turbulence (i.e., the order of the size of the embers) on evolving firebrands; b) investigate the effect of thermally-driven turbulent winds due to heterogeneous spatiotemporally variable buoyant forces on firebrand transport, and c) explore the effect of mechanically-driven turbulence structures due to surface topography on firebrand transport.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.