The evolution of vortices in a turbulent boundary layer
Kempka, Steven Norman
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https://hdl.handle.net/2142/23019
Description
Title
The evolution of vortices in a turbulent boundary layer
Author(s)
Kempka, Steven Norman
Issue Date
1989
Doctoral Committee Chair(s)
Dunn, William E.
Department of Study
Mechanical Science and Engineering
Discipline
Mechanical Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Language
eng
Abstract
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.
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