The evolution of vortices in a turbulent boundary layer

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Science and Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Kempka, Steven Norman

Contributors dc:contributor

• Dunn, William E.

• Engineering, Mechanical

Statement dc:rights

• Copyright 1989 Kempka, Steven Norman

Language dc:language

eng

Identifier

AAI8924858
(UMI)AAI8924858

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/23019