{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/50749"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/50749","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Cross-plane stereo-PIV measurements of a turbulent boundary layer over highly irregular roughness","abstract":"The characteristics of a turbulent boundary layer overlying a complex roughness topography were explored with stereo particle-image velocimetry measurements in the wall-normal--spanwise plane. The roughness under consideration was replicated from a turbine blade damaged by deposition of foreign materials containing a broad range of topographical scales arranged in a highly irregular manner. Such roughness is representative of that encountered in a broad range of practical flow systems, such as turbine-blade arrays, heat exchangers and marine vehicle surfaces, for example. Thus, understanding its impact on flow in a controlled laboratory environment is meant to provide a bridge to more fully understanding roughness effects in these practical scenarios. Low-frame-rate stereo particle image velocimetry (PIV) measurements were conducted in the cross-flow, spanwise-wall-normal, plane at moderate Reynolds number. The single-point turbulence statistics in this plane displayed strong spanwise heterogeneity, in particular spanwise-alternating low- and high-momentum flow pathways in the mean flow marked by enhanced Reynolds stresses and turbulent kinetic energy. The spanwise regions between high- and low-momentum flow pathways were occupied by swirling motions, suggesting the generation and sustainment of turbulent secondary flows due to the spanwise heterogeneity of the complex roughness under consideration. High-frame-rate stereo PIV measurements were then conducted in the same spanwise-wall-normal plane and at the same Reynolds number to study the turbulent kinetic energy and Reynolds shear stress content of the flow as a function of scale in the presence of this complex roughness. Similar to that observed for the mean and turbulence quantities noted above, frequency spectra of streamwise velocity at fixed wall-normal location also display strong dependence on spanwise position. In particular, the roughness promotes enhanced turbulent kinetic energy content of the large-scale motions and smaller-scale motions. Depending on spanwise location, pre-multiplied spectra highlight significant modification of the energy content of the very large-scale motions due to roughness when compared to smooth-wall flow. Interestingly, spanwise locations where high-momentum pathways reside in the mean flow embody higher turbulent kinetic energy and Reynolds shear stress content at streamwise scales of the very-large-scale motions compared to that observed at spanwise locations of low-momentum pathways.","abstract_html":"The characteristics of a turbulent boundary layer overlying a complex roughness topography were explored with stereo particle-image velocimetry measurements in the wall-normal--spanwise plane. The roughness under consideration was replicated from a turbine blade damaged by deposition of foreign materials containing a broad range of topographical scales arranged in a highly irregular manner. Such roughness is representative of that encountered in a broad range of practical flow systems, such as turbine-blade arrays, heat exchangers and marine vehicle surfaces, for example. Thus, understanding its impact on flow in a controlled laboratory environment is meant to provide a bridge to more fully understanding roughness effects in these practical scenarios. Low-frame-rate stereo particle image velocimetry (PIV) measurements were conducted in the cross-flow, spanwise-wall-normal, plane at moderate Reynolds number. The single-point turbulence statistics in this plane displayed strong spanwise heterogeneity, in particular spanwise-alternating low- and high-momentum flow pathways in the mean flow marked by enhanced Reynolds stresses and turbulent kinetic energy. The spanwise regions between high- and low-momentum flow pathways were occupied by swirling motions, suggesting the generation and sustainment of turbulent secondary flows due to the spanwise heterogeneity of the complex roughness under consideration. High-frame-rate stereo PIV measurements were then conducted in the same spanwise-wall-normal plane and at the same Reynolds number to study the turbulent kinetic energy and Reynolds shear stress content of the flow as a function of scale in the presence of this complex roughness. Similar to that observed for the mean and turbulence quantities noted above, frequency spectra of streamwise velocity at fixed wall-normal location also display strong dependence on spanwise position. In particular, the roughness promotes enhanced turbulent kinetic energy content of the large-scale motions and smaller-scale motions. Depending on spanwise location, pre-multiplied spectra highlight significant modification of the energy content of the very large-scale motions due to roughness when compared to smooth-wall flow. Interestingly, spanwise locations where high-momentum pathways reside in the mean flow embody higher turbulent kinetic energy and Reynolds shear stress content at streamwise scales of the very-large-scale motions compared to that observed at spanwise locations of low-momentum pathways.","abstract_has_math":false,"creators":["Barros, Julio"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Theoretical & Applied Mechans","degree_department":null,"school":null,"contributors":["Christensen, Kenneth T.","Vanka, Surya Pratap","Pantano-Rubino, Carlos A.","Chamorro, Leonardo P."],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2014,"date_issued":"2014-09-16","date_published":"2014-09-16","updated_at":"2026-07-22T22:25:41Z","subjects":["boundary layer","turbulent flow","roughness","particle image velocimetry (PIV)"],"languages":["en"],"rights":["Copyright 2014 Julio Barros"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/2142/50749","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Christensen, Kenneth T.","Vanka, Surya Pratap","Pantano-Rubino, Carlos A.","Chamorro, Leonardo P."]},{"key":"dc:creator","label":"Author","values":["Barros, Julio"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2014-09-16","2014-08","2014-09-16T17:26:10Z"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Theoretical & Applied Mechans"]},{"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":["boundary layer","turbulent flow","roughness","particle image velocimetry (PIV)"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2014 Julio Barros"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/50749"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["The characteristics of a turbulent boundary layer overlying a complex roughness topography were explored with stereo particle-image velocimetry measurements in the wall-normal--spanwise plane. The roughness under consideration was replicated from a turbine blade damaged by deposition of foreign materials containing a broad range of topographical scales arranged in a highly irregular manner. Such roughness is representative of that encountered in a broad range of practical flow systems, such as turbine-blade arrays, heat exchangers and marine vehicle surfaces, for example. Thus, understanding its impact on flow in a controlled laboratory environment is meant to provide a bridge to more fully understanding roughness effects in these practical scenarios. Low-frame-rate stereo particle image velocimetry (PIV) measurements were conducted in the cross-flow, spanwise-wall-normal, plane at moderate Reynolds number. The single-point turbulence statistics in this plane displayed strong spanwise heterogeneity, in particular spanwise-alternating low- and high-momentum flow pathways in the mean flow marked by enhanced Reynolds stresses and turbulent kinetic energy. The spanwise regions between high- and low-momentum flow pathways were occupied by swirling motions, suggesting the generation and sustainment of turbulent secondary flows due to the spanwise heterogeneity of the complex roughness under consideration. High-frame-rate stereo PIV measurements were then conducted in the same spanwise-wall-normal plane and at the same Reynolds number to study the turbulent kinetic energy and Reynolds shear stress content of the flow as a function of scale in the presence of this complex roughness. Similar to that observed for the mean and turbulence quantities noted above, frequency spectra of streamwise velocity at fixed wall-normal location also display strong dependence on spanwise position. In particular, the roughness promotes enhanced turbulent kinetic energy content of the large-scale motions and smaller-scale motions. Depending on spanwise location, pre-multiplied spectra highlight significant modification of the energy content of the very large-scale motions due to roughness when compared to smooth-wall flow. Interestingly, spanwise locations where high-momentum pathways reside in the mean flow embody higher turbulent kinetic energy and Reynolds shear stress content at streamwise scales of the very-large-scale motions compared to that observed at spanwise locations of low-momentum pathways.","Item withdrawn by Laura Spradlin (lspradl2@illinois.edu) on 2014-07-07T15:26:08Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 1 Barros_Julio.pdf: 63776484 bytes, checksum: 21c5d2e410b14188beb65eb091c6e439 (MD5)","Made available in DSpace on 2014-09-16T17:26:10Z (GMT). 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Such roughness is representative of that encountered in a broad range of practical flow systems, such as turbine-blade arrays, heat exchangers and marine vehicle surfaces, for example. Thus, understanding its impact on flow in a controlled laboratory environment is meant to provide a bridge to more fully understanding roughness effects in these practical scenarios. Low-frame-rate stereo particle image velocimetry (PIV) measurements were conducted in the cross-flow, spanwise-wall-normal, plane at moderate Reynolds number. The single-point turbulence statistics in this plane displayed strong spanwise heterogeneity, in particular spanwise-alternating low- and high-momentum flow pathways in the mean flow marked by enhanced Reynolds stresses and turbulent kinetic energy. The spanwise regions between high- and low-momentum flow pathways were occupied by swirling motions, suggesting the generation and sustainment of turbulent secondary flows due to the spanwise heterogeneity of the complex roughness under consideration. High-frame-rate stereo PIV measurements were then conducted in the same spanwise-wall-normal plane and at the same Reynolds number to study the turbulent kinetic energy and Reynolds shear stress content of the flow as a function of scale in the presence of this complex roughness. Similar to that observed for the mean and turbulence quantities noted above, frequency spectra of streamwise velocity at fixed wall-normal location also display strong dependence on spanwise position. In particular, the roughness promotes enhanced turbulent kinetic energy content of the large-scale motions and smaller-scale motions. Depending on spanwise location, pre-multiplied spectra highlight significant modification of the energy content of the very large-scale motions due to roughness when compared to smooth-wall flow. Interestingly, spanwise locations where high-momentum pathways reside in the mean flow embody higher turbulent kinetic energy and Reynolds shear stress content at streamwise scales of the very-large-scale motions compared to that observed at spanwise locations of low-momentum pathways.","Item withdrawn by Laura Spradlin (lspradl2@illinois.edu) on 2014-07-07T15:26:08Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 1 Barros_Julio.pdf: 63776484 bytes, checksum: 21c5d2e410b14188beb65eb091c6e439 (MD5)","Made available in DSpace on 2014-09-16T17:26:10Z (GMT). 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