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dc.rights.licenseRestricted to current Rensselaer faculty, staff and students. Access inquiries may be directed to the Rensselaer Libraries.
dc.contributorAmitay, Michael
dc.contributorLetchford, C. W.
dc.contributorSahni, Onkar
dc.contributorHicken, Jason
dc.contributorKopp, Greg A.
dc.contributor.authorMoore, Daniel Millyn
dc.date.accessioned2021-11-03T09:22:21Z
dc.date.available2021-11-03T09:22:21Z
dc.date.created2021-02-22T15:33:01Z
dc.date.issued2020-08
dc.identifier.urihttps://hdl.handle.net/20.500.13015/2625
dc.descriptionAugust 2020
dc.descriptionSchool of Engineering
dc.description.abstractThis dissertation promotes a deeper understanding of the various roles carried out by the content within a bluff body shear layer. Experimental data achieve high resolution in space and time through the use of particle image velocimetry, hot wire, and pressure taps, all focused in the regions closest to the origins of the shear layer. By varying a focused set of parameters, most importantly among them the Reynolds number, this work demonstrates that although the shear layer may appear to play a secondary role in the generation of aerodynamics loads its mechanics enhance the roles played by small disturbances in addition to large gusts in the freestream. Moreover, the vulnerability to external disturbances complicates the inspection of these shear layers whose behavior without the presence of disturbances contrasts some conventional wisdom of bluff body aerodynamics and their behavior with respect to a changing Reynolds number. Reynolds numbers vary approximately from $10^4$ up to $10^6$ and the bodies tested range from a square prism to a long, blunt flat plate, each with sharp corners. Testing facilities include those on campus at Rensselaer Polytechnic Institute and Florida International University.
dc.description.abstractResults show that under a changing Reynolds number, a simple phenomenological scaling is sufficient to reconcile the shear layer behavior via two independently collected data types, where the locally defined transition distance is the most important length scale. The transition distance reduces as the Reynolds number increases, along with an attendant increase in frequency. While observable in the correct reference frame on bluffer bodies (e.g., the square prism), more elongated bodies (3:1, and 5:1 rectangular prisms) demonstrate this behavior in a more compelling manner. These bodies further reveal additional Reynolds-sensitive behavior seemingly contrasting with the commonly held notion that all sharp-edged bodies exhibit invariant behavior with respect to a changing Reynolds number. The mechanisms behind this are explained using two-point correlation methods demonstrating the coupling between adjacent hydrodynamic (in)stability modes. A lack of coupling on the 5:1 rectangle explains some of the behavioral traits of the shear layer without the modulation by external forces. For this reason much the subsequent analysis deals with this shape exclusively.
dc.description.abstractThe addition of freestream disturbances is carried out at Reynolds numbers approaching full scale. These data, in the form of surface pressures collected on the front face and beneath the separation bubble, suggest that the mechanism of peak pressures does not solely come from the amplitude of a single length scale as some have suggested. Rather, the peak events are simultaneous fluctuations of several length scales. This finding is subsequently discussed as it contains consequences for those modeling in wind tunnel environments or those who are unable recreate the natural wind spectrum in its entirety.
dc.description.abstractThe notion of energetic scales is defined in the transitioning shear layer by the length scales most rapidly converting mean flow energy into turbulent kinetic energy. These scales are observed to migrate along the frequency axis as the shear layer matures and transitions. The shift in scale size inspires the inspection of select terms in the Karman-Howarth-Monin-Hill equation, and a scale-space domain where the interscale energy flux terms are evaluated and discussed. The analysis demonstrates that the smallest observed scales are at least partially responsible for supplying the energy of larger scales, contrary to traditional turbulence teachings that follow the uni-directional energy cascade.
dc.language.isoENG
dc.publisherRensselaer Polytechnic Institute, Troy, NY
dc.relation.ispartofRensselaer Theses and Dissertations Online Collection
dc.subjectMechanical engineering
dc.titleEnergetic scales in bluff body shear layers, a Reynolds number investigation
dc.typeElectronic thesis
dc.typeThesis
dc.digitool.pid180370
dc.digitool.pid180371
dc.digitool.pid180372
dc.rights.holderThis electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author.
dc.description.degreePhD
dc.relation.departmentDept. of Mechanical, Aerospace, and Nuclear Engineering


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