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Title: Study of turbulence and wall shear stress in unsteady flow over smooth and rough wall surfaces
Author: Seddighi-Moormani, Mehdi
ISNI:       0000 0004 2710 6403
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2011
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Flows over hydraulically smooth walls are predominant in turbulence studies whereas real surfaces in engineering applications are often rough. This is important because turbulent flows close to the two types of surface can exhibit large differences. Unfortunately, neither experimental studies nor theoretical studies based on conventional computational fluid dynamics (CFD) can give sufficiently accurate, detailed information about unsteady turbulent flow behaviour close to solid surfaces, even for smooth wall cases. In this thesis, therefore, use is made of a state of the art computational method “Direct Numerical Simulation (DNS)” to investigate the unsteady flows. An “in-house” DNS computer code is developed for the study reported in this thesis. Spatial discretization in the code is achieved using a second order, finite difference method. The semi-implicit (Runge-Kutta & Crank-Nicholson) time advancement is incorporated into the fractional-step method. A Fast Fourier Transform solver is used for solving the Poisson equation. An efficient immersed Boundary Method (IBM) is used for treating the roughness. The code is parallelized using a Message Passing Interface (MPI) and it is adopted for use on a distributed-memory computer cluster at University of Aberdeen as well as for use at the UK’s national high-performance computing service, HECToR. As one of the first DNS of accelerating/decelerating flows over smooth and rough walls, the study has produced detailed new information on turbulence behaviours which can be used for turbulence model development and validations. The detailed data have enabled better understanding of the flow physics to be developed. The results revealed strong non-equilibrium and anisotropic behaviours of turbulence dynamics in such flows. The preliminary results on the rough wall flow show the response of turbulence in the core and wall regions, and the relationship between the axial and the other components are significantly different from those in smooth wall flows.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Turbulence ; Surface roughness ; Fluid dynamics ; Direct numerical simulation