{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/87761"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/87761","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Experimental Study of Low-Order Models of Highly-Irregular Roughness and Their Impact on Turbulent Boundary Layers","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.","abstract_html":"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.","abstract_has_math":false,"creators":["Mejia Alvarez, Ricardo"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Theoretical and Applied Mechanics","degree_department":null,"school":null,"contributors":["Christensen, Kenneth T."],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2015,"date_issued":"2015-09-28T16:23:53Z","date_published":"2015-09-28T16:23:53Z","updated_at":"2026-07-22T22:26:30Z","subjects":["Engineering, Mechanical"],"languages":["eng"],"rights":[],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["(MiAaPQ)AAI3455830"],"render_values":[{"text":"(MiAaPQ)AAI3455830","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/2142/87761","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Christensen, Kenneth T."]},{"key":"dc:creator","label":"Author","values":["Mejia Alvarez, Ricardo"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2015-09-28T16:23:53Z","10000-01-01","2010"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Theoretical and Applied Mechanics"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Engineering, Mechanical"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/87761","(MiAaPQ)AAI3455830"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["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). 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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). 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