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Title:Experimental Study of Low-Order Models of Highly-Irregular Roughness and Their Impact on Turbulent Boundary Layers
Author(s):Mejia-Alvarez, Ricardo
Doctoral Committee Chair(s):Christensen, Kenneth T.
Department / Program:Theoretical and Applied Mechanics
Discipline:Theoretical and Applied Mechanics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Engineering, Mechanical
Abstract:The stereo-PIV measurements deep within the roughness sublayer at y = 0.047delta reveal a wealth of information about roughness-induced effects, including the tendency of the roughness to promote 'channeling' of the flow in the form of low- and high-momentum pathways as noted in contour maps of the mean velocity defect. Similarly, enhanced turbulent and vortical activity is observed both between and along the spanwise boundaries of these streamwise-elongated large-scale pathways. Taken together, these observations support the idea that these persistent low-momentum pathways might represent the statistical imprint of trains of hairpin vortex packets that are channeled along preferred paths over the roughness. Conditional averaging and two-point correlations of velocity further support these structural observations, particularly clear large-scale streamwise coherence of these motions. Of interest, while the M = 5 results show important differences from the full-surface results, the M = 16 results are virtually indistinguishable fromthose of the full surface, including in the single-point turbulence statistics as well as the analysis of the average spatial structure. This consistency is not simply qualitative but is indeed quantitative as the magnitudes of the M = 16 model single-point statistics mirror those of the full surface as do the spatial locations of the low- and high-momentum pathways identified in the mean velocity defect results as well as the enhanced turbulent and vortical activity along the spanwise boundaries of these large-scale motions. Hence, these observations provide significant evidence supporting the importance of the intermediate topographical scales in setting the flow conditions within the roughness sublayer, not only in a statistical sense but also in a structural sense.
Issue Date:2010
Type:Text
Language:English
Description:183 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2010.
URI:http://hdl.handle.net/2142/87761
Other Identifier(s):(MiAaPQ)AAI3455830
Date Available in IDEALS:2015-09-28
Date Deposited:2010


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