First Advisor

Raúl Bayoán Cal

Term of Graduation

Summer 2022

Date of Publication

7-13-2022

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Mechanical Engineering

Department

Mechanical and Materials Engineering

Language

English

Subjects

Orthogonal decompositions, Fluid dynamics, Turbulence

DOI

10.15760/etd.8043

Physical Description

1 online resource (vi, 50 pages)

Abstract

Multi-scale rough patches are present in topologies such as urban canopies (cities) and natural landscapes (forests, ocean floors). The flow over such canopies is three-dimensional, with turbulent structures known as secondary flows present in the boundary layer due to the difference in rough surface heterogeneities. Three dimensional instantaneous velocities are analyzed within the roughness sublayer over three generations of multi-scale rough patches at nine vertical planes using particle image velocimetry obtained experimentally. The secondary structures present in the flow are identified in the form of Reynolds and dispersive fluctuations. Proper orthogonal decomposition is employed to characterize the imprint of the flow. The energy contained within the flow structures is represented through the modes, with the first few modes being the dominant modes and containing the most turbulent kinetic energy. Using these modes, corresponding Reynolds and dispersive stresses are reconstructed thus filtering the flow domains and demonstrating the coherence of both the Reynolds and dispersive stresses for the generations. The dispersive stresses can be reconstructed with fewer modes than the Reynolds stresses, and are approximately an order of magnitude smaller. The reconstructed domains are used to compute the wall shear stress through the integrated momentum equation and related to the flow coherence. The contribution of dispersive stresses to the wall shear stress is small due to the dispersive stresses being concentrated at the wall, while that of Reynolds stress is significant. This affects the low-order calculation of the wall shear stress for each generation. The rough surface generations with the highest Reynolds numbers associated with the momentum thickness also have the highest wall shear stress, but all experience similar trends in the amount of modes required to reach full representation.

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Persistent Identifier

https://archives.pdx.edu/ds/psu/38762

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