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Experimental Study of Low-Order Models of Highly-Irregular Roughness and Their Impact on Turbulent Boundary Layers text Christensen, Kenneth T. Mejia Alvarez, Ricardo 2015-09-28T16:23:53Z 2015-09-28T16:23:53Z 10000-01-01 2010 2010 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. Made available in DSpace on 2015-09-28T16:23:53Z (GMT). No. of bitstreams: 2 license.txt: 4848 bytes, checksum: 96035ab3f5e1c23cc7138a224ce498bd (MD5) 3455830.pdf: 148535852 bytes, checksum: 9f0da4909feb0e05bd29761d7111f1ca (MD5) Previous issue date: 2010 Embargo set by: Seth Robbins for item 89042 Lift date: Forever Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs U of I Only 183 p. Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2010. http://hdl.handle.net/2142/87761 (MiAaPQ)AAI3455830 eng Engineering, Mechanical Theoretical and Applied Mechanics Theoretical and Applied Mechanics University of Illinois at Urbana-Champaign Dissertation Ph.D.