Heat Transfer Model for the Assemblage of Firebrands Over Surface Fuels

火种阵雨，也被称为余烬袭击，是由于余烬在远离火线的植被或结构部件上的产生，运输和积累而引起的现场火灾。虽然现场火灾有助于野火的快速增长，并且已知是造成荒地城市界面事件的重大损害的原因，但目前对从火焰到暴露表面的热量（能量）传递机制的理解是不完整的。这个项目的主要目的是建立从火焰沉积到接收表面的热量（能量）传递的基本知识。该项目的成果通过启用基于物理的现场火灾点火模块，直接为野火模拟器提供信息，从而更准确地预测和估计野火风险。该项目还将包括教育活动，如指导和培训本科生和研究生，与利益相关者和从业者的接触，以及在不同的工程/科学学科之间建立合作，以应对火灾科学的挑战。该项目的主要目标是使用系统的、可扩展的和准确的定量方法来量化从累积的火种到接收表面的热量传递。具体而言，该项目执行以下任务：首先，使用四向耦合方法进行数值模拟，以确定边界层内燃烧特性及其相互作用对惰性平面上沉积模式的影响。其次，利用x射线计算机断层扫描（XCT）将表面燃料形态纳入计算领域，并定量地辨别其对火焰沉积模式和传热的影响。第三，利用高保真模拟生成的数据，开发数据驱动的传热模型，并测试其准确性。开发的模型使研究结果适用于大规模（可操作）野火模拟器，最终开发了基于物理的现场火灾点火模块。研究结果有望深入了解点火点火过程中的主要传热机制，并建立一个计算框架，用于量化从反应粒子到周围壁面的能量传递。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Firebrand shower, also known as ember attack, is the ignition of spot fires due to the generation, transport, and accumulation of embers over vegetation or structural components away from the active fire lines. Although spot fires contribute to rapid wildfire growth and are known to be responsible for significant damages incurred at the Wildland Urban Interface incidents, the current understanding of the heat (energy) transfer mechanisms from firebrands to the exposed surfaces is incomplete. The primary aim of this project is to establish a fundamental knowledge of the heat (energy) transfer from firebrand depositions to the recipient surfaces. The outcomes of this project directly inform wildfire simulators by enabling a physics-based spot fire ignition module leading to more accurate forecasts and estimation of wildfire risk. The project will also encompass educational activities such as mentoring and training undergraduate and graduate students, engagement with stakeholders and practitioners, and creating collaborations between different engineering/scientific disciplines to address challenges in fire science.The main objective of this project is to quantify the heat transfer from the accumulated firebrands to the recipient surface using a systematic, scalable, and accurate quantitative approach. Specifically, the project performs the following tasks: First, conducting numerical simulations using a four-way coupled method to identify the effects of firebrand properties and their interactions within the boundary layer on the deposition patterns over an inert flat surface. Second, incorporating surface fuel morphology into the computational domain, using X-Ray Computed Tomography (XCT), and quantitatively discern its influence on firebrand deposition patterns and heat transfer. Third, leveraging the generated data from high-fidelity simulations, developing a data-driven heat transfer model, and testing its accuracy. The developed model makes the findings applicable for large-scale (operational) wildfire simulators, culminating in the development of a physics-based spot fire ignition module. The results are expected to provide insights into dominant heat transfer mechanisms involved in the spot fire ignition process and establish a computational framework for quantifying the energy transfer from reacting particles to the surrounding walls.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.