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

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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.