CAREER: Physics and modeling of flame extinction in presence of evaporating droplets

对火焰熄灭的基本了解在促进能源安全、环境可持续性、航空旅行安全和适时灭火方面发挥着核心作用。在过去的几十年里，国际燃烧界对火焰熄灭进行了广泛的研究，但基础研究的范围大多局限于气态火焰。在实际的燃烧系统中，液滴普遍存在，如航空燃烧室中的燃油喷雾和用于污染物减排或灭火的水滴。当与已建立的气态火焰相互作用时，液滴通过蒸发、稀释、后续反应、湍流调制和辐射热传递等物理过程引入额外的灭火机制。因此，本项目的主要目的是对在液滴存在的情况下控制火焰熄灭过程的关键因素提供一个基本的了解和定量的描述。该项目还将包括重要的教育活动，包括一个新的“虚拟热流体实验室”课程和一本由研究数据支持的配套书籍。在开展研究和教育活动的同时，还将实施两个外联方案。首先，一个针对高中教师的教育项目将使用研究数据作为提高高中生计算能力的独特途径。其次，研究人员将与当地博物馆馆长合作，展示来自研究项目的艺术设计，并吸引代表不足的群体进入STEM职业生涯。这个项目的目标是解决关于不均匀的热量、动量和质量传递影响火焰消光极限的机制的知识空白。随机液滴湍流引入了额外的热汇/源和在消光极限附近的微妙平衡的不均匀反应性。将采用正则逆流构型来表示火焰-液滴相互作用的基本过程。将采用开放源码的计算框架，其中将仔细设计数值算法，以确保各种物理过程之间的必要耦合。所提出的数值模型和求解算法将纳入湍流多相流和消光化学研究的最新进展，为更准确的深入计算研究铺平道路。将建立一种方法，将来自三维直接数值模拟的信息与一维模拟湍流模拟相结合，以实现有效和可靠的参数分析。利用降阶模型，建立标度关系，为此类问题的临界时间尺度和长度尺度提供定量描述。该项目的成功实施将使工程应用中稳健的降阶建模成为可能，例如航空燃烧室的稀薄喷发和使用水雾灭火。该奖项反映了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。

Fundamental understanding of flame extinction plays a central role in promoting energy security, environmental sustainability, air-travel safety and opportune fire suppression. Flame extinction has been extensively studied by the international combustion community in the past few decades, however, the scope of fundamental studies has mostly been limited to gaseous flames. Droplets, such as fuel sprays in aeronautical combustors and water droplets in pollutant reduction or fire suppression, are ubiquitous in practical combustion systems. When interacting with an established gaseous flame, droplets introduce additional mechanisms to extinguish a flame, through physical processes such as vaporization, dilution, subsequent reactions, modulation of turbulence, and radiative heat transfer. Therefore, the principal aim of this project is to provide a fundamental understanding and a quantitative description of key factors governing the flame extinction process in presence of droplets. The project will also encompass significant educational activities, including a new “Virtual Thermal Fluids Lab” course and a companion book that are enabled by the research data. In conjunction with the research and educational activities, two outreach programs will be implemented. First, an educational program for high school teachers will use the research data as a unique avenue to enhance the computational literacy of high school students. Second, researchers will work with local museum curators to showcase artistic designs that are derived from the research program and to attract underrepresented groups into STEM careers. The goal of this project is to address the knowledge gap pertaining to the mechanism through which heterogeneous heat, momentum, and mass transfer impact the extinction limits for flames.Stochastic droplet-laden turbulent flow introduces additional heat sinks/sources and nonuniform reactivity to the delicate balance near the extinction limit. A canonical counterflow configuration will be adopted to represent the fundamental processes of flame-droplet interactions. An open-source computational framework will be adopted, where numerical algorithms will be carefully designed to ensure necessary coupling between various physical processes. The proposed numerical models and solution algorithms will incorporate latest development from the study of turbulent multiphase flows and extinction chemistry, paving the way for more accurate in-depth computational studies. A methodology will be established to combine information from three-dimensional direct numerical simulations with one-dimensional modeled turbulent simulations to enable efficient and reliable parametric analysis. Using the reduced-order models, scaling relations will be established, which will provide a quantitative description of critical time and length scales in such problems. Successful execution of this project will enable robust reduced-order modeling in engineering applications, such as lean-blowoff in aeronautical combustors and fire suppression using water mists.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.