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dc.contributor.authorYuan, Junlin
dc.contributor.otherQueen's University (Kingston, Ont.). Theses (Queen's University (Kingston, Ont.))en
dc.date2011-10-14 13:11:21.394en
dc.date2011-10-17 11:19:08.063en
dc.date.accessioned2011-10-17T18:33:42Z
dc.date.available2011-10-17T18:33:42Z
dc.date.issued2011-10-17
dc.identifier.urihttp://hdl.handle.net/1974/6846
dc.descriptionThesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2011-10-17 11:19:08.063en
dc.description.abstractLarge-eddy simulations are carried out to study the combined effects of roughness and favourable pressure gradient in boundary layer flows, where the high acceleration (on smooth walls) may cause flow reversion to the quasi-laminar state. A sand-grain roughness model is used, with the no-slip boundary condition modeled by an immersed boundary method. The properties and accuracies of the scheme are studied, the roughness model is validated, and the spatial-resolution requirements are determined. The roughness model is applied to boundary layers subject to mild or strong acceleration, with simulations carried out underlining the effects of three parameters: the acceleration parameter, the roughness height, and the inlet Reynolds number. The roughness effects are limited to the roughness sublayer; the outer layer is affected indirectly only, through the changes that roughness causes in the relaminarization and retransition processes. The roughness significantly affects the inner-layer quantities like the friction velocity and the friction coefficient, while the local Reynolds number, the outer-layer mean velocity, as well as the Reynolds stresses beyond the roughness sublayer, are not sensitive to the roughness. The acceleration decreases the Reynolds stresses in the overlap region and promotes a laminar-like velocity profile. The acceleration leads to stabilization of near-wall structures and causes one-dimensional turbulence. The roughness generates small-scale structures at the bottom wall, which disturb the larger structures originally stabilized by the pressure gradient, leading to a decrease in the Reynolds-stress anisotropy. Roughness increases the Reynolds stresses in the roughness sublayer and tends to restore the fully turbulence flow early. The inlet Reynolds number affects the flow stability by determining the viscous length scale compared to the roughness length scales, and by determining how far the roughness effect extents into the boundary layer.en_US
dc.languageenen
dc.language.isoenen_US
dc.relation.ispartofseriesCanadian thesesen
dc.rightsThis publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.en
dc.subjectRelaminarizationen_US
dc.subjectRoughnessen_US
dc.subjectLarge-eddy simulationen_US
dc.subjectTurbulent boundary layersen_US
dc.subjectFree-stream accelerationen_US
dc.titleLarge-Eddy Simulations of Accelerating Boundary Layer Flows Over Rough Surfacesen_US
dc.typeThesisen_US
dc.description.degreeMasteren
dc.contributor.supervisorPiomelli, Ugoen
dc.contributor.departmentMechanical and Materials Engineeringen


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