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dc.contributor.authorAwasthi, Manujen_US
dc.date.accessioned2015-11-14T09:01:11Z
dc.date.available2015-11-14T09:01:11Z
dc.date.issued2015-11-13en_US
dc.identifier.othervt_gsexam:6483en_US
dc.identifier.urihttp://hdl.handle.net/10919/64158
dc.description.abstractMeasurements have been performed to understand the sound source mechanism in turbulent boundary layer flow over two and three-dimensional surface discontinuities whose height is smaller than the incoming boundary layer thickness. The work was performed in two different types of boundary layers: a wall-jet flow and a conventional high Reynolds boundary layer. In the wall-jet flow, measurements of far field sound from two-dimensional forward facing steps, gaps with rounded corners and swept forward facing steps with rounded corners were made. The sound from a forward facing step is shown to exhibit effects of non-compactness. Rounding the step corner results in consistent drop in sound levels but the directivity of the sound field remains unchanged. The sound from gaps is dominated by the forward step component and remains unaffected by rounding of the backward step portion. The sound from swept forward facing steps was found to approximately obey an acoustic sweep independence principle up to a sweep angle of 30 deg when the spanwise inhomogeneity in the flow is accounted for using a simple source distribution model. Sweep independence is also observed for steps with corner rounding radii up to 25% of the step height. The work performed in the high Reynolds number boundary layer included measurements on forward facing steps with rounded corners and a three-dimensional circular embossment with the same height as the forward step. The highest Reynolds number based on discontinuity height achieved in this work was approximately 93,000. The results show that rounding the forward step corner has the same qualitative effect on far field sound as in the wall-jet boundary layer. Quantitatively, for similar boundary layer edge velocity the sound is higher than in the wall-jet flow. The near field measurements show that the separation bubble downstream of the step shrinks as the step corner is rounded while the bubble upstream remains unaffected by it. The unsteady surface force in the lower half of the vertical face of the step was found to be independent of corner rounding. The force on the downstream surface shows similar character within the separation bubble for each rounding but decays faster with increasing downstream distance due to reduced bubble size. The unsteady force measurements were applied to the theory of Glegg et al. (2014) and the resultant of the unsteady forces on the vertical face and downstream surface placed at the top corner of the step is shown to qualitatively describe the far field sound. The acoustic sweep independence principle was applied to the far field sound from the circular embossment and it has been shown that the sound from the three-dimensional geometry can be predicted with reasonable accuracy using sound from a two-dimensional forward step with the same span.en_US
dc.format.mediumETDen_US
dc.publisherVirginia Techen_US
dc.rightsThis Item is protected by copyright and/or related rights. Some uses of this Item may be deemed fair and permitted by law even without permission from the rights holder(s), or the rights holder(s) may have licensed the work for use under certain conditions. For other uses you need to obtain permission from the rights holder(s).en_US
dc.subjectForward step noiseen_US
dc.subjectgap noiseen_US
dc.subjectswept forward step noiseen_US
dc.subjectcircular embossment noiseen_US
dc.subjectsurface pressure fluctuations and unsteady surface forceen_US
dc.titleSound Radiated from Turbulent Flow over Two and Three-Dimensional Surface Discontinuitiesen_US
dc.typeDissertationen_US
dc.contributor.departmentAerospace and Ocean Engineeringen_US
dc.description.degreePh. D.en_US
thesis.degree.namePh. D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
thesis.degree.disciplineAerospace Engineeringen_US
dc.contributor.committeechairDevenport, William J.en_US
dc.contributor.committeememberPaterson, Eric G.en_US
dc.contributor.committeememberGlegg, Stewarten_US
dc.contributor.committeememberLowe, Kevin T.en_US
dc.contributor.committeememberAlexander, William Nathanen_US


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