Numerical Modeling of Non-Premixed Flame-Wall Interactions in Turbulent Boundary Layer Flows

提案编号：cts -0553508首席研究员：Trouve， Arnaud c .机构：马里兰大学学院公园提案题目：湍流边界层流动中非预混火焰壁相互作用的数值模拟火焰壁相互作用（FWI）在许多燃烧系统中起着重要作用。例如，在内燃机中，冷却壁与短火焰壁距离的结合会导致火焰熄灭，而在热效率和污染倾向方面，FWI会对发动机性能产生负面影响。在航空推进和发电应用中也观察到类似的效果，特别是考虑到最近设计更紧凑、更小（中尺度或微尺度）燃烧室的趋势；与之相关的更高的表面体积比和更短的火焰壁距离导致火焰壁相互作用对燃烧系统性能的影响更大。围场火灾是另一个燃烧问题，FWI在其中起着重要作用。例如，垂直可燃壁的燃烧是一种通用构型，燃料在浮力驱动的壁边界层内释放和消耗，整个燃烧过程可以被认为是FWI。发现FWI现象会导致火焰和壁面动力学的显著变化：在冷壁面附近，由于局部淬火事件，火焰强度降低，而气固热流密度在火焰接触处达到峰值。然而，尽管有这些发现，在工程级计算流体动力学（CFD）工具中，FWI现象仍然被忽视，需要将用于描述湍流边界层的近似壁面边界条件适应于FWI的发生。本项目的总体目标是响应这一需求，并将当前墙层模型的功能扩展到描述火焰-墙相互作用。该项目的范围集中在浮力驱动的非预混火焰与惰性或易燃墙壁的相互作用上，这是火灾应用中发现的一个普遍问题。建模工作是在大涡模拟（LES）方法的框架内进行的。提出的研究计划的主要组成部分是：基于直接数值模拟的火焰-壁相互作用的详细研究；利用具有解析壁面层的LES对火焰-壁面相互作用进行了详细研究；一个模型开发组件，旨在使壁层模型适应FWI的处理；第一模型验证组件，该组件基于使用已建模或已解析的壁层进行的LES模拟之间的比较；基于LES模拟和实验数据比较的第二个模型验证组件。在第二个验证组件中，所选择的实验配置与Ahmad &amp； Faeth研究的经典湍流垂直壁火实验相对应。总而言之，本项目的智力价值包括提高对FWI配置的知识，并增强对火灾应用的模拟能力。拟议的工作也有望为与发动机应用相关的类似开发铺平道路。更广泛的影响包括对使用现代计算工具开发急需的基于工程（基于性能）的消防安全方法的贡献。该项目还有一个教育部分，解决以下问题：需要在计算火灾建模领域教育合格的工作人员；需要为理学士学生提供研究经验，以加强本科教育；需要通过开发新的研究生水平的计算火灾建模课程来开发跨学科的工程课程。

Award AbstractProposal Number: CTS-0553508Principal Investigator: Trouve, Arnaud C.Institution: University of Maryland College ParkProposal Title: Numerical Modeling of Non-Premixed Flame-Wall Interactons in Turbulent Boundary Layer Flows Flame-wall interactions (FWI) play an important role in many combustion systems. For instance in Internal Combustion engines, cooled walls combined with occurrences of short flame-wall distances result in flame quenching and FWI has a negative impact on engine performance, both in terms of thermal efficiency and pollution propensity. Similar effects are observed in aeronautical propulsion and power-generation applications, especially given the recent trends towards the design of more compact, smaller (meso- or micro-scale) combustion chambers; the associated higher surface-to-volume ratios and shorter flame-wall distances result in a larger impact of flame-wall interactions on the combustion system performance. Enclosure fires are another combustion topic in which FWI plays an important role. For instance, the burning of a vertical flammable wall is a generic configuration where the fuel is released and consumed within the buoyancy-driven wall boundary layer and the entire combustion process may be considered as FWI.FWI phenomena are found to result in significant changes in the flame and wall dynamics: the flame strength is reduced near cold wall surfaces by local quenching events while the gas-solid heat flux takes peak values at flame contact. Despite these findings, however, FWI phenomena remain neglected in engineering-level Computational Fluid Dynamics (CFD) tools and there is a need to adapt the approximate wall boundary conditions used to describe turbulent boundary layers to the occurrence of FWI. The general objective of the present project is to respond to that need and extend the capabilities of current wall-layer models to the description of flame-wall interactions. The scope of the project is focused on interactions of buoyancy-driven non-premixed flames with inert or flammable walls, a generic problem found in fire applications. The modeling effort is developed in the framework of a large eddy simulation (LES) approach.The main components of the proposed research program are: a detailed study of flame-wall interactions based on direct numerical simulations; a detailed study of flame-wall interactions using LES with resolved wall layers; a model development component aimed at adapting wall-layer models to the treatment of FWI; a first model validation component based on a comparison between LES simulations performed with modeled or resolved wall layers; a second model validation component based on a comparison between LES simulations and experimental data. In this second validation component, the selected experimental configuration corresponds to the classical turbulent vertical wall fire experiment studied by Ahmad & Faeth.In summary, the intellectual merit of the present project includes advancing knowledge in, and enhancing simulation capabilities for, FWI configurations of interest to fire applications. The proposed work is also expected to pave the way for similar developments relevant to engine applications. The broader impacts include a contribution to the development of a much-needed engineering-based (performance-based) approach to fire safety using modern computational tools. The project has also an educational component that addresses the following issues: the need to educate a qualified work force in the area of computational fire modeling; the need to enhance Undergraduate education by providing a research experience to BS students; the need to develop an interdisciplinary engineering curriculum through the development of a new Graduate-level computational fire modeling class.