Theses and Dissertations from UMD

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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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2004 - 200912010 - 20131

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Subject: search.filters.subject.Turbulence Modeling

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    Large Eddy Simulation of Boundary Layer Combustion
    (2013) Bravo, Luis Giovanni; Trouve, Arnaud C; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Numerical simulations of turbulent non-premixed flames occurring in the presence of solid surfaces is a prevalent topic of interest due to the complexity of the near wall physics and the technical modeling challenges it presents. Near wall combustion phenomena is relevant in a variety of combusting environments including but not limited to the occurrence of fire spread, as a result of a heating load to a flammable wall leading to fire growth in enclosure settings; and in engine combustion configurations where the interaction with a cooled surface combined with occurrences of short flame wall distances can lead to extinction events adversely affecting combustion performance. The interaction between the flame and surface can result in a reduction of flame strength near the cold wall region while gas phase heat fluxes can take peak values at flame contact. To address the aforementioned modeling challenges, an advanced computational fluid dynamics (CFD) solver has been developed by adapting a preexisting numerical simulation solver from a boundary layer code to a code with variable mass density and combustion capabilities to produce high-fidelity simulations of turbulent non-premixed wall-flames. A series of verification studies have been developed using several benchmark laminar flow problems for the following canonical configurations: a binary diffusion controlled mixing problem, Poiseuille flow with heat transfer, and classical Blasius boundary layer flow. The turbulence LES modeling capability is validated by performing wall-resolved heated/non-heated turbulent channel flow and transpired boundary layer simulations to capture the effects of heat and mass transfer on the turbulent eddy structure and statistics. Lastly, an application of a simplified non-premixed wall flame configuration is presented in which the fuel corresponds to pyrolysis products supplied by a thermally-degrading flat sample of polymethyl methacrylate (PMMA) and the oxidizer corresponds to a cross-flow of ambient air with controlled mean velocity and turbulence intensities. Comparisons between numerical results and experimental data are made in terms of flame length, wall surface heat flux and flame structure and the ability of the solver in modeling non-premixed turbulent wall-flames is successfully demonstrated. The solver extends the present state of the art in fire modeling (limited to laminar flows) by providing a high quality numerical tool to study the heat transfer aspects of turbulent wall flame phenomena
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    Critical Evaluation and Development of One-Equation Near-Wall Turbulence Models
    (2004-12-20) Diaz, Ricardo H.; Barlow, Jewel B; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A systematic evaluation of one-equation near-wall turbulence models is completed and a new model is developed. The study includes five one-equation near- wall models and one two-equation model such that the performance of the one-equation models can be viewed in context of the performance of this more widely used class of models. It is found that the majority of one-equation near-wall models do not reproduce the variation of the Reynolds shear stress near the wall, do not reproduce the dissipation at the wall, and do not predict the dissipation well in the region near the wall for a boundary layer flow. The new model is found to provide improved performance for the boundary layer and a wavy-wall channel. Specifically, it is found that the new model predicts the turbulent kinetic energy and dissipation in closer agreement with direct numerical simulation data than existing one-equation models for the boundary layer and provides improved predictions of the shear stress distribution for the wavy-wall channel. It is found that the one-equation near-wall models generally predict the shear stress distribution for the wavy-wall channel with greater accuracy than the two-equation model. In addition, it is shown that computations using the one-equation models are less sensitive to wall spacing than those using the two-equation model. This suggests that one-equation near-wall models, and in particular the new model, are ideal for engineering computations of practical flows where computational expense may be a significant factor entering into the choice of turbulence model.