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dc.contributor.advisorGlezer, Arien_US
dc.contributor.authorNygaard, Kris Jacob.
dc.creatorNygaard, Kris Jacob.en_US
dc.date.accessioned2011-10-31T17:39:36Z
dc.date.available2011-10-31T17:39:36Z
dc.date.issued1991en_US
dc.identifier.urihttp://hdl.handle.net/10150/185497
dc.description.abstractThe formation and evolution of secondary vortical structures in a plane mixing layer subjected to spanwise-nonuniform excitation has been studied in a closed-return water facility. It is shown that secondary vortices may result from spanwise-nonuniformities in the nominally two-dimensional vorticity layer close to the flow partition, or from spanwise core deformations of the primary vortices further downstream. These distinctly different mechanisms are excited by time-harmonic wavetrains with spanwise amplitude or phase variations, respectively, synthesized by a mosaic of surface film heaters flush-mounted on the flow partition. The appearance of the secondary vortical structures is accompanied by significant distortions in transverse distributions of the streamwise velocity component. Inflection points, which are not present in corresponding velocity distributions of the unforced flow, suggest the formation of locally unstable regions of large shear in which broadband perturbations, already present in the base flow, undergo rapid amplification. This amplification is followed by breakdown to turbulence thus producing the small-scale motion necessary for mixing transition. The present investigation further shows that the flow is extremely receptive to spanwise-periodic amplitude excitation at any wavelength synthesizable by the heater mosaic. Spanwise-periodic phase excitation leads to substantial deformations of the primary vortices, although the receptivity of the flow appears to have a short wavelength cutoff. Spanwise-nonuniform amplitude and phase excitations at a subharmonic frequency of the Kelvin-Helmholtz instability result in complex pairing interactions of the primary vortices.
dc.language.isoenen_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.subjectDissertations, Academicen_US
dc.subjectMechanical engineering.en_US
dc.titleSpanwise-nonuniform excitation of a plane mixing layer.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.identifier.oclc710837087en_US
thesis.degree.grantorUniversity of Arizonaen_US
thesis.degree.leveldoctoralen_US
dc.contributor.committeememberBayly, Bruce J.en_US
dc.contributor.committeememberLamb, George L.en_US
dc.contributor.committeememberBalsa, Thomas F.en_US
dc.contributor.committeememberChen, Chaun F.en_US
dc.contributor.committeememberChampagne, Francis H.en_US
dc.identifier.proquest9127713en_US
thesis.degree.disciplineAerospace and Mechanical Engineeringen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.namePh.D.en_US
refterms.dateFOA2018-06-15T05:26:10Z
html.description.abstractThe formation and evolution of secondary vortical structures in a plane mixing layer subjected to spanwise-nonuniform excitation has been studied in a closed-return water facility. It is shown that secondary vortices may result from spanwise-nonuniformities in the nominally two-dimensional vorticity layer close to the flow partition, or from spanwise core deformations of the primary vortices further downstream. These distinctly different mechanisms are excited by time-harmonic wavetrains with spanwise amplitude or phase variations, respectively, synthesized by a mosaic of surface film heaters flush-mounted on the flow partition. The appearance of the secondary vortical structures is accompanied by significant distortions in transverse distributions of the streamwise velocity component. Inflection points, which are not present in corresponding velocity distributions of the unforced flow, suggest the formation of locally unstable regions of large shear in which broadband perturbations, already present in the base flow, undergo rapid amplification. This amplification is followed by breakdown to turbulence thus producing the small-scale motion necessary for mixing transition. The present investigation further shows that the flow is extremely receptive to spanwise-periodic amplitude excitation at any wavelength synthesizable by the heater mosaic. Spanwise-periodic phase excitation leads to substantial deformations of the primary vortices, although the receptivity of the flow appears to have a short wavelength cutoff. Spanwise-nonuniform amplitude and phase excitations at a subharmonic frequency of the Kelvin-Helmholtz instability result in complex pairing interactions of the primary vortices.


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