Large-scale structures and the spatial evolution of wakes behind axisymmetric bluff bodies.

Persistent Link:
http://hdl.handle.net/10150/185647
Title:
Large-scale structures and the spatial evolution of wakes behind axisymmetric bluff bodies.
Author:
Cannon, Steven Cary.
Issue Date:
1991
Publisher:
The University of Arizona.
Rights:
Copyright © 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.
Abstract:
The wakes behind a variety ofaxisymmenic bodies were investigated with flow visualization and hot-wire measurements. The main objective of this study was to correlate changes in the time-averaged features of the wake with changes in the characteristics of the coherent large-scale structure resulting from changing the solidity of the wake generator or by introducing periodic disturbances to force the wake. The use of an axisymmenic probe holder permitted instantaneous decomposition of the axialvelocity field into temporal and azimuthal Fourier modes. Increases in the body solidity resulted in nearly proportional increases in the size of the mean wake boundary. For the non-shedding (low body solidity) wakes, flow visualization shows that the amplitude of discernible large-scale structure is small in comparison to the wake diameter, and there is no evidence of a recirculation region. For the shedding wakes, flow visualization reveals large-scale structure with amplitude that is comparable in size to the wake diameter, and a recirculation region is observed that oscillates in axial extent Fourier analysis of velocity measurements discloses that the temporal scale of the coherent large-scale structure for a non-shedding wake decreases in value with downstream distance while the corresponding scale for a shedding wake is constant Significant changes in the both the time-averaged features of the wake and in the large-scale structure usually occurred only when the forcing frequency was near the natural shedding frequency (within ± 25%). Those time-averaged features changed by forcing include the drag, the mean- and variance-profile shapes, and the size of the wake. The mean profile was observed to change from a regular shape to that which resembles a variance profile. Forcing results in a number of peaks being present in 2-D spectra plots, most of which are the result of non-linear interactions of the forcing wave with the natural shedding frequency. The flow visualization reveals that those peaks which are harmonics or subharmonics of the forcing frequency may be more prominent than the forcing frequency if they are closer to the natural shedding frequency of the unforced wake.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Base flow (Aerodynamics).
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Aerospace and Mechanical Engineering; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Champagne, F.H.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleLarge-scale structures and the spatial evolution of wakes behind axisymmetric bluff bodies.en_US
dc.creatorCannon, Steven Cary.en_US
dc.contributor.authorCannon, Steven Cary.en_US
dc.date.issued1991en_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.description.abstractThe wakes behind a variety ofaxisymmenic bodies were investigated with flow visualization and hot-wire measurements. The main objective of this study was to correlate changes in the time-averaged features of the wake with changes in the characteristics of the coherent large-scale structure resulting from changing the solidity of the wake generator or by introducing periodic disturbances to force the wake. The use of an axisymmenic probe holder permitted instantaneous decomposition of the axialvelocity field into temporal and azimuthal Fourier modes. Increases in the body solidity resulted in nearly proportional increases in the size of the mean wake boundary. For the non-shedding (low body solidity) wakes, flow visualization shows that the amplitude of discernible large-scale structure is small in comparison to the wake diameter, and there is no evidence of a recirculation region. For the shedding wakes, flow visualization reveals large-scale structure with amplitude that is comparable in size to the wake diameter, and a recirculation region is observed that oscillates in axial extent Fourier analysis of velocity measurements discloses that the temporal scale of the coherent large-scale structure for a non-shedding wake decreases in value with downstream distance while the corresponding scale for a shedding wake is constant Significant changes in the both the time-averaged features of the wake and in the large-scale structure usually occurred only when the forcing frequency was near the natural shedding frequency (within ± 25%). Those time-averaged features changed by forcing include the drag, the mean- and variance-profile shapes, and the size of the wake. The mean profile was observed to change from a regular shape to that which resembles a variance profile. Forcing results in a number of peaks being present in 2-D spectra plots, most of which are the result of non-linear interactions of the forcing wave with the natural shedding frequency. The flow visualization reveals that those peaks which are harmonics or subharmonics of the forcing frequency may be more prominent than the forcing frequency if they are closer to the natural shedding frequency of the unforced wake.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectBase flow (Aerodynamics).en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineAerospace and Mechanical Engineeringen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorChampagne, F.H.en_US
dc.contributor.committeememberBayly, B.J.en_US
dc.contributor.committeememberKerschen, E.J.en_US
dc.contributor.committeememberChampagne, F.H.en_US
dc.identifier.proquest9208047en_US
dc.identifier.oclc702674829en_US
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