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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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 or Dissertation (PhD)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Library of Congress Subject Headings (LCSH):	Turbulence -- Mathematical models
Date:	March 2012
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
URI:	http://wrap.warwick.ac.uk/id/eprint/47055

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