ISS: Flame Spread Response to Non-steady Airflow

荒野地区附近的社区，特别是美国西部的社区，受到野地火灾严重程度和频率增加的威胁。与此同时，这些大火在更大的地理区域造成了空气污染。这项提议寻求通过提高预测火灾蔓延和增长的能力来降低这些火灾的严重性和影响。野地大火是非常动态的，风和燃料负荷迅速变化，但迄今为止的许多研究都是基于稳定分析。最近的研究已经提供了对火焰增长的更完整的了解，特别是来自火焰的间歇性燃料加热的作用，但总体上，缺乏关于非稳定(周期性或间歇性)火焰传播的基础研究。本项目的目标是研究蔓延火焰对非稳定强迫流动的响应，以更好地预测野火蔓延。这将通过混合对流流动(浮力流动和强迫流动)下的地面实验以及纯强迫流动下的微重力实验来实现。这些实验将描述和解释非定常流动条件下的瞬变火焰行为。这些知识将使研究界深入了解非稳定流动过程在野火传播中的作用。本项目将使用实验和计算模型来研究瞬时火焰行为影响非稳定并发气流传播火焰的物理机制。该项目的目标是通过研究火焰间歇性燃料加热对火灾蔓延速度的影响来更好地预测野火蔓延。最近的研究发现，在某些火灾条件下，间歇性火焰加热过程可能是主要的传热过程，导致火灾蔓延，这是现有模型无法预测的。因此，有必要发展一种野火蔓延的“可验证的物理理论”。该项目旨在通过研究非稳定气流辅助的火焰传播的相关基本问题，为发展这一理论的目标做出贡献。本文提出用非定常(周期)外强迫流来模拟由浮力不稳定和/或湍流边界层引起的间歇流。包含微重力实验将能够消除浮力效应，并更好地描述非定常流动。这项拟议的研究将是第一个，如果不是第一个，专门调查火焰传播对非稳定、并行气流的响应的实验研究之一。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Communities near wildland areas, particularly those in the western United States, are threatened by increases in wildland fire severity and frequency. At the same time these fires contribute to air pollution over much larger geographical areas. This proposal seeks to reduce the severity and impact of these fires by improving the ability to predict their spread and growth. Wildland fires are very dynamic with rapidly changing winds and fuel loads yet much research to date is based on steady analysis. Recent research has provided a more complete understanding of fire growth, particularly the role of intermittent fuel heating from the flame, but overall, there is an absence of fundamental research on non-steady (periodic or intermittent) flame spread. The objective of this project is to study a spreading flame’s response to a non-steady forced flow to better predict wildfire spread. This will be accomplished through terrestrial experiments under mixed convection flow (buoyant and forced flow) as well as microgravity experiments with purely forced flow. These experiments will characterize and help explain transient flame behavior under non-steady flow conditions. This knowledge will provide the research community with insight into the role of non-steady flow processes in wildfire spread. This project will examine the physical mechanisms by which transient flame behavior impacts a spreading flame with a non-steady concurrent airflow using experiments and computational modelling. The goal of this project is to better predict wildfire spread by examining the role of intermittent fuel-heating from flames on the rate of fire spread. Recent research has found that intermittent flame heating processes can be the dominant heat transfer process under certain fire conditions, resulting in fire spread that is not predicted by current models. Thus, there is a need to develop a “verifiable physical theory” of wildfire spread. This project seeks to contribute towards the goal of developing such a theory by studying the related fundamental problem of flame spread aided by non-steady airflow. Here it is proposed to use a non-steady (periodic) external forced flow to experimentally simulate the intermittent flow induced by the buoyant instabilities and/or a turbulent boundary layer. Inclusion of microgravity experiments will enable removal of buoyancy effects and better characterization the non-steady flow. The proposed research will be one of the first, if not the first, experimental study specifically investigating the response of spreading flames to a non-steady, concurrent airflow.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.