Fluid Dynamics and Surface Pressure Fluctuations of Turbulent Boundary Layers Over Sparse Roughness

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dc.contributor.authorVarano, Nathaniel Daviden
dc.contributor.committeechairSimpson, Roger L.en
dc.contributor.committeememberMason, William H.en
dc.contributor.committeememberDevenport, William J.en
dc.contributor.committeememberRoy, Christopher J.en
dc.contributor.committeememberRagab, Saad A.en
dc.contributor.departmentAerospace and Ocean Engineeringen
dc.date.accessioned2014-03-14T20:09:48Zen
dc.date.adate2010-04-29en
dc.date.available2014-03-14T20:09:48Zen
dc.date.issued2010-01-29en
dc.date.rdate2010-04-29en
dc.date.sdate2010-04-16en
dc.description.abstractTurbulent boundary layers over rough surfaces are a common, yet often overlooked, problem of practical engineering importance. Development of correlations between boundary layer parameters that can be used in turbulence models and the surface geometry is the only practical option for solving these problems. Experiments have been performed on a two-dimensional zero pressure gradient turbulent boundary layer over sparsely spaced hemispherical roughness elements of 2 mm diameter. Laser Doppler velocimetry was used to measure all three components of velocity. The friction velocity was calculated using an integral momentum balance. Comparisons were made with various fitting methods that assume the von Kármán constant is appropriate for rough walls. Results indicate that this is not the case, and that the slope of the semi-logarithmic portion of the mean streamwise profile may be a function of the ratio of inner and outer length scales. Comparisons were also made between various correlations that relate the surface geometry to the behavior of the mean velocity profile. In general, the existing correlations achieved a reasonable agreement with the data within the estimated uncertainties. A detailed study of the local turbulent structure around the roughness elements was performed. It was found that, in contrast to `sharper-edged' elements such as cylinders, an elevated region of TKE and Reynolds shear stress was found downstream of the element below the peak. This can be explained by the delay in separation of the flow coming over the top of the element due to the smooth curvature of the element. Surface pressure fluctuation measurements were made as well using a dual microphone noise reduction technique. There have only been a few past experiments on the surface pressure fluctuations under rough wall boundary layers. However, it has been shown that the spectra of the wall fluctuations can be used to predict the far-field noise spectrum [1,2]. Therefore it is been the goal of this research to verify existing correlations between the surface pressure fluctuation spectrum and the surface geometry as well as develop new correlations that provide insight into the interactions between the turbulent motions in the flow surface pressure.en
dc.description.degreePh. D.en
dc.identifier.otheretd-04162010-154904en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-04162010-154904/en
dc.identifier.urihttp://hdl.handle.net/10919/26918en
dc.publisherVirginia Techen
dc.relation.haspartVarano_ND_D_2010.pdfen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectroughnessen
dc.subjectlaser Doppler velocimetryen
dc.subjectskin frictionen
dc.subjectTurbulenceen
dc.subjectboundary layeren
dc.subjectsurface pressureen
dc.titleFluid Dynamics and Surface Pressure Fluctuations of Turbulent Boundary Layers Over Sparse Roughnessen
dc.typeDissertationen
thesis.degree.disciplineAerospace and Ocean Engineeringen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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