2026-09-21T11:52:50Z https://www.ideals.illinois.edu/oai-pmh

oai:www.ideals.illinois.edu:2142/50749 2023-07-11 col_2142_5131 col_2142_14787 com_2142_5130 com_2142_9630 com_2142_234

2014-09-16 2014-08 Christensen, Kenneth T. Christensen, Kenneth T. Vanka, Surya Pratap Pantano-Rubino, Carlos A. Chamorro, Leonardo P. Barros, Julio 2014-09-16T17:26:10Z 2014-09-16T17:26:10Z 2014-08 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). No. of bitstreams: 2 Julio_Barros.pdf: 63774546 bytes, checksum: 2f5ae6c3e6103c1b8e8c62bbfa4b7bbd (MD5) license.txt: 4062 bytes, checksum: d11617b7f114508784df34497642bd62 (MD5) http://hdl.handle.net/2142/50749 en Copyright 2014 Julio Barros boundary layer turbulent flow roughness particle image velocimetry (PIV) Cross-plane stereo-PIV measurements of a turbulent boundary layer over highly irregular roughness text Mechanical Sci & Engineering 1917 Theoretical & Applied Mechans 0242 University of Illinois at Urbana-Champaign Dissertation Ph.D. PHD:Theor&Appl Mechanics -UIUC 10KS0242PHD