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dc.contributor.supervisor Tachie, Mark F. (Mechanical and Manufacturing Engineering) en_US
dc.contributor.author Tsikata, Jonathan Mawuli
dc.date.accessioned 2012-12-20T16:27:05Z
dc.date.available 2012-12-20T16:27:05Z
dc.date.issued 2012-12-20
dc.identifier.uri http://hdl.handle.net/1993/14164
dc.description.abstract This thesis is an experimental study of turbulent flows over smooth and rough walls in a channel that consists of an upstream parallel section to produce a fully developed channel flow and a diverging section to produce an adverse pressure gradient (APG) flow. The roughness elements used were two-dimensional square ribs of nominal height k = 3 mm. The ribs were secured to the lower wall of the channel and spaced to produce the following three pitches: 2k, 4k and 8k, corresponding to d-type, intermediate and k-type rough walls, respectively. For each rough wall type, the ribs were inclined at 90°, 45° and 30° to the approach flow. The velocity measurements were performed using a particle image velocimetry technique. The results showed that rib roughness enhanced the drag characteristics, and the degree of enhancement increased with increasing pitch. The level of turbulence production and Reynolds stresses were significantly increased by roughness beyond the roughness sublayer. It was observed that the population, sizes and the level of organization of hairpin vortices varied with roughness and more intense quadrant events were found over the smooth wall than the rough walls. APG reinforced wall roughness in augmenting the equivalent sand grain roughness height, turbulence production and Reynolds stresses. APG also reduced the sizes of the hairpin packets but strengthened the quadrant events in comparison to the results obtained in the parallel section. The secondary flow induced by inclined ribs significantly altered the distributions of the flow characteristics across the span of the channel. Generally, the mean flow was less uniform close to the trailing edge of the ribs compared to the flows at the mid-span and close to the leading edge of the ribs. The Reynolds stresses and hairpin packets were distinctly larger close to the trailing edge of the ribs. Rib inclination also decreased the drag characteristics and significantly modified the distributions of the Reynolds stresses and quadrant events. In the parallel section, the physical sizes of the hairpin packets were larger over 45° ribs whereas in the diverging section, the sizes were larger over perpendicular ribs. en_US
dc.rights info:eu-repo/semantics/openAccess
dc.subject Rough wall en_US
dc.subject Adverse pressure gradient en_US
dc.subject Rib inclination en_US
dc.subject Turbulent flow en_US
dc.subject Coherent structures en_US
dc.subject Hairpin vortices en_US
dc.subject Hairpin vortex packet en_US
dc.subject Drag en_US
dc.subject Turbulence en_US
dc.subject d-type rough wall en_US
dc.subject intermediate type rough wall en_US
dc.subject k-type rough wall en_US
dc.subject Roughness en_US
dc.title Experimental Study of Turbulent Flow over Inclined Ribs in Adverse Pressure Gradient en_US
dc.type info:eu-repo/semantics/doctoralThesis
dc.type doctoral thesis en_US
dc.degree.discipline Mechanical and Manufacturing Engineering en_US
dc.contributor.examiningcommittee Wang, Bing-Chen (Mechanical and Manufacturing Engineering) Chen, Ying (Biosystems Engineering) Castillo, Luciano (Texas Tech University, USA) en_US
dc.degree.level Doctor of Philosophy (Ph.D.) en_US
dc.description.note February 2013 en_US


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