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A numerical investigation of three-dimensional unsteady turbulent channel flow subjected to temporal acceleration
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Talha, Tariq (2012) A numerical investigation of three-dimensional unsteady turbulent channel flow subjected to temporal acceleration. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b2569027~S1
Abstract
Investigation of turbulence response during constant temporal acceleration and
deceleration can assist in improving the understanding of turbulence evolution and flow physics. Such
flows have potential importance in engineering applications for
example the air
flow through the main trachea during the breathing cycle experience
temporal acceleration and deceleration. The previous experimental and theoretical
investigations based on conventional computational
fluid dynamics (CFD) modelling
could not provide the detailed information about turbulence response in the near-wall region in such types of
flows. In particular, the response of near-wall structures
has not been studied for turbulent
flow with temporal acceleration and deceleration.
In the present study, turbulent
flows involving temporal acceleration and deceleration has been investigated using DNS and LES.
A fully implicit fractional step method is implemented in the present study. The
Navier-Stokes equations are discretised using finite volume method. Second-order-
implicit Crank-Nicolson method is used for temporal discretisation for the convective
and viscous terms. Second-order accuracy of spatial discretisation is achieved using
four neighbouring points to calculate velocity gradients. A uniform grid is used in
the streamwise and spanwise directions while a non-uniform grid is employed in the
wall-normal direction. The numerical implementation has been validated for three
test cases. The dynamic subgrid-scale model has been implemented for LES calculations. The LES model implementation has been validated through comparison
with benchmark data available in literature.
As one of the first DNS of accelerating turbulent
flow, this study has produced
a comprehensive database of turbulent statistics which can be used for unsteady
turbulence modelling and validation. The detailed investigation has substantially
enhanced the understanding of turbulence response for such
flows. The
flow physics
has been studied in detail using turbulent kinetic energy budget analysis, vorticity
analysis, anisotropy invariant maps and energy spectra. The evolution of new turbulent structures during the acceleration has been investigated using low-speed streaks
and λ2 plots and many interesting
ow characteristics have been found. The effect
of different acceleration rates has been studied using LES. The turbulence propaga-
tion in the core region has been studied for different acceleration rates. Turbulent
flow subjected to constant temporal deceleration has also been investigated using
LES. The effect of different deceleration rates has been also studied. The turbulent
flow response to temporal deceleration has been analysed using the rms velocity and
vorticity, kinetic energy budget and Reynolds stress anisotropy tensor analysis.
Item Type: | Thesis (PhD) | ||||
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Subjects: | T Technology > TA Engineering (General). Civil engineering (General) | ||||
Library of Congress Subject Headings (LCSH): | Turbulence -- Mathematical models | ||||
Official Date: | March 2012 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | School of Engineering | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Chung, Yongmann M. | ||||
Sponsors: | Pakistan ; University of Warwick. School of Engineering | ||||
Extent: | xviii, 257 leaves : ill., charts | ||||
Language: | eng |
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