A novel application of flame hole dynamics to consistent turbulent nonpremixed combustion modeling

运输和能源转换设备中使用的大多数系统都是通过在湍流中燃烧燃料来提供动力的。在减少污染物排放的同时，改进目前和未来的多种燃料原料是一项主要的技术挑战。化学活性通常集中在薄火焰中，通常被称为小火焰，嵌入在否则不起反应的湍流流场中。这些小火焰是燃烧过程的一维模型，不能自然地解释流动中出现的多维现象，在流动中，有限速率化学效应或优先传输效应是重要的。边缘火焰是由弯曲的边缘组成的二维结构，可以在部分熄灭的火焰的边界上出现。在非预混火焰中，边缘火焰由预混段(稀薄和/或富含燃料)组成，扩散火焰在后面消耗多余的反应物。边缘火焰与湍流流动有关，在湍流中，有限速率的化学过程导致燃烧熄灭/重燃；例如，在高应变(强烈湍流活动区域)的湍流扩散火焰中戳出的孔洞附近。如有必要，应将它们并入数值模拟中，以获得全面的、物理上真实的描述。该项目的目标是开发、验证和验证湍流燃烧的结构火焰模型，该模型将真实的气体化学、火焰结构和流体力学一致地结合在一起。此外，该方案通过发展一种可在湍流模拟中普遍应用的形式主义和闭包，将这些火焰抽象思想扩展到大涡模拟(LES)。该项目涉及将小火焰和边缘火焰的结构及其动力学整合在一种方法中，以实现准确和有效的数值模拟。拟议的计划侧重于通过建模闭包中的第一原则来减少经验主义并提高可预测性。拟议的研究将在理解和预测湍流燃烧流动的能力方面产生重大影响，在流动条件和燃料化学方面具有普遍性。加强对这些流动的预测有许多工业和社会效益：能源转换效率对成本和污染有直接影响。此外，计算思维和网络资源使用方面的进步和创新将促进工程和应用数学教育，这反过来又有助于扩大国家科学技术人力资源基础。已完成工作的更广泛影响是通过在技术和科学界发表出版物和演讲，以及教育和培训学生和青年科学家，为今后在学术界和工业界工作做准备。

Most systems used in transportation and energy conversion devices are powered through combustion of fuel in turbulent flows. Improvement of current and future versatile fuel feedstock, while reducing pollutant emissions, is a primary technological challenge. The chemical activity is typically concentrated within thin flames, usually called flamelets, which are embedded in an otherwise non-reacting turbulent flow field. These flamelets are one-dimensional models of the combustion process and are unable to account naturally for multi-dimensional phenomena appearing in flows where finite-rate-chemistry effects or preferential transport effects are important. Edge flames are two-dimensional structures consisting of curved edges that can arise at the boundary of a partially extinguished flame. In non-premixed flames, edge flames consist of premixed segments (lean and/or rich in fuel), with a diffusion flame that consumes the excess reactants trailing behind. Edge flames are relevant in turbulent flows where finite-rate chemical processes lead to extinction/reignition of the combustion; for example, near holes poked in turbulent diffusion flames at high strains (regions of strong turbulence activity). They should be incorporated in numerical simulations, where necessary, for a comprehensive and physically realistic description. The objective of the project is to develop, verify, and validate structural flame models for turbulent combustion that couple consistently real gas chemistry, flame structure, and hydrodynamics. Furthermore, the proposal pursues an extension of these flame-abstraction ideas to large-eddy simulation (LES) by developing a formalism and closure that can be applied with generality in turbulent simulations. The project involves integrating flamelet and edge flame structures and their dynamics in a methodology for accurate and efficient numerical simulations. The proposed program focuses on reducing empiricism and improving predictability through first principles in the modeling closures. The proposed research will make a significant impact in the understanding and in the capability to predictively model turbulent combusting flows with generality in terms of flow conditions and fuel chemistry. Enhancements in the prediction of these flows have numerous industrial and societal benefits: energy conversion efficiency has a direct effect on cost and pollution. Moreover, the advances and innovations in computational thinking and in the use of cyber resources will enhance the engineering and applied mathematics education, which in turn helps extend the national human-resources base for science and technology. The broader impact of the accomplished work is through publications and presentations in the technical and scientific community, and by educating and training students and young scientists for future careers in academia and industry.