Cressman, John Robert
(2004)
experimental studies in non-equilibrium physics.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
This work is a collection of three experiments aimed at studyingdifferent facets of non-equilibrium dynamics. Chapter I concernsstrongly compressible turbulence, which turns out to be verydifferent from incompressible turbulence. The focus is on thedispersion of contaminants in such a flow. This type of turbulencecan be studied, at very low mach number, by measuring the velocityfields of particles that float on a turbulently stirred body ofwater. It turns out that in the absence of incompressibility, theturbulence causes particles to cluster rather than to disperse.The implications of the observations are far reaching and includethe transport of pollutants on the oceans surface, phytoplanktongrowth, as well as industrial applications.Chapter II deals with the effects of polymer additives on dragreduction and turbulent suppression, a well-known phenomenon thatis not yet understood. In an attempt to simplify the problem, theeffects of a polymer additive were investigated in a vortex streetformed in a flowing soap film. Measurements suggest that anincrease in elongational viscosity is responsible for asubstantial reduction in periodic velocity fluctuations. Thisstudy also helps to illuminate the mechanism responsible forvortex separation in the wake of a bluff body.Chapter III describes an experiment designed to test a theoreticalapproach aimed at generalizing the classical fluctuationdissipation theorem (FDT). This theorem applies to systems drivenonly slightly away from thermal equilibrium, whereas ours, aliquid crystal undergoing electroconvection, is so stronglydriven, that the FDT does not apply. Both theory and experimentfocus on the flux in global power fluctuations. Physicallimitations did not permit a direct test of the theory, however itwas possible to establish several interesting characteristics ofthe system: the source of the fluctuations is the transient defectstructures that are generated when the system is driven hard. Itis found that the power fluctuations are spatially uncorrelated,but strongly correlated in time and even quasi-periodic.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
|
| Date: |
16 January 2004 |
| Date Type: |
Completion |
| Defense Date: |
20 August 2003 |
| Approval Date: |
16 January 2004 |
| Submission Date: |
12 December 2003 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Dietrich School of Arts and Sciences > Physics |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
compressible; non-equilibrium; turbulence |
| Other ID: |
http://etd.library.pitt.edu/ETD/available/etd-12122003-003508/, etd-12122003-003508 |
| Date Deposited: |
10 Nov 2011 20:10 |
| Last Modified: |
15 Nov 2016 13:54 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/10336 |
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