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An investigation of turbulent boundary layers with streamwise and spanwise pressure gradients
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Pearce, Nicholas F. (2013) An investigation of turbulent boundary layers with streamwise and spanwise pressure gradients. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b2688227~S1
Abstract
An experimental comparison is made between two turbulent boundary layers
produced in a low-speed water channel subjected to different pressure gradient
distributions. Both
flows involve identical favourable streamwise components, generated
via a lateral contraction of the
flow area; and in the second case, an additional
spanwise gradient is imposed by curving the walls.
The measurement system and methods are developed in full, with rigorous
testing and validation allowing the uncertainty and accuracy of the results to be
estimated. Hot-wire anemometry is employed to take measurements of velocity
using miniature single-film probes. A Hydrogen bubble visualisation system enables
an inspection of the coherent turbulent structures in the boundary layer near the
wall.
The mean-velocity measurements show a continued rise in the Reynolds number
downstream accompanied by a fall in the coefficient of friction, in spite of a relatively
high streamwise acceleration. This unorthodox behaviour was found to occur
for both
flows. In response to the acceleration, changes in the statistical moments of
streamwise velocity show an increased dominance of high velocity
fluctuations near
the wall. This corresponds with the results of the structure visualisations which
reveal a rise in the mean spanwise spacing of the low-speed
fluid elements.
The pressure gradients of the two cases are generated using a novel approach
which aims to make the effects from each strain easier to evaluate. The additional
spanwise component in the second case induced a cross
ow in the boundary layer
which reached 11% that of the local external velocity. Despite this, the measurements
and low-speed streaks show the turbulence to be relatively insensitive to this
level of three-dimensionality.
A simple numerical method is presented to model the development of the
low-speed
fluid streaks in different mean-velocity distributions. Using this model,
greater cross
flow magnitudes in the boundary layer are tested for which a positive
streak dependence is found.
Item Type: | Thesis (PhD) | ||||
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Subjects: | T Technology > TA Engineering (General). Civil engineering (General) | ||||
Library of Congress Subject Headings (LCSH): | Turbulent boundary layer, Turbulence | ||||
Official Date: | May 2013 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | School of Engineering | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Lockerby, Duncan; Denisenko, Petr | ||||
Extent: | xx, 245 leaves : illustrations, charts. | ||||
Language: | eng |
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