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oai:www.ideals.illinois.edu:2142/23019 2023-07-10 col_2142_5131 col_2142_14787 com_2142_5130 com_2142_9630 com_2142_234

Dunn, William E. Kempka, Steven Norman 2011-05-07T13:59:16Z 2011-05-07T13:59:16Z 10000-01-01 1989 Most scientists would agree that the greatest unsolved problem of fluid mechanics is turbulence. Turbulence is not only an intellectual challenge to mathematicians and theorists, it is also of practical interest since the highly dissipative and dispersive nature of turbulence has a significant impact on many applications. Over the years, many investigations have yielded descriptions of turbulent velocity fields and hypotheses for the physical basis of turbulence; however, the fundamental physics of turbulence remain unknown. In this investigation, the evolution of a perturbed vortex tube near a boundary is examined in order to gain insight into turbulent boundary layer phenomena. A Lagrangian vortex model is used to describe the vortex tube evolution, including the influence of shear. Based on numerical calculations, it is shown that small perturbations evolve into large horseshoe-shaped vortex structures which have been observed in laboratory experiments and direct numerical solutions of the Navier-Stokes equations. Additionally, horseshoe-shaped vortices are shown to collapse and form vortex rings which have also been reported in experimental investigations. The motion of evolving vortices is shown to provide a physical basis for enhanced momentum transport and observed inclinations of vorticity. In addition, collections of vortices are shown to provide an inviscid basis for mean velocity gradients and random-appearing, yet well correlated, velocity fluctuations. Made available in DSpace on 2011-05-07T13:59:16Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 8924858.pdf: 8973719 bytes, checksum: 365121b1a0c8d4dd029db9f9050aa7fe (MD5) Previous issue date: 1989 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T15:01:37Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:29:14-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission ETDs are only available to UIUC Users without author permission U of I Only AAI8924858 (UMI)AAI8924858 http://hdl.handle.net/2142/23019 eng Copyright 1989 Kempka, Steven Norman Engineering, Mechanical The evolution of vortices in a turbulent boundary layer text Mechanical Science and Engineering Mechanical Science and Engineering University of Illinois at Urbana-Champaign Dissertation Ph.D.