Boundary shear stress distribution and flow structures in trapezoidal channels

Ansari, Kamran (2011) Boundary shear stress distribution and flow structures in trapezoidal channels. PhD thesis, University of Nottingham.

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The commercially available Computational Fluid Dynamics (CFD) software ANSYS-CFX version 11 (2008) is employed to predict the distribution of the bed and sidewall shear stresses in trapezoidal open channels. The investigation includes computation of wall shear stress (1) directly, using CFD for a range of channels layouts (straight, turning, with ridges), and (2), building on the division line concept initially formulated by Leighly in 1932 and later by Einstein in 1942, through the evaluation of the Guo and Julien (2005) equations, as proposed by Cacqueray et al. (2009). These equations include the two complex integral terms II and III, pertaining to viscous and secondary current effects, have been analysed for each cross section, for straight channels.

The CFD predictions are validated first against the experimental results of Tominaga et al. (1989) to ensure that the models used are appropriate. Once this is done, the impact of (1) the variation of the slant angle of the sidewalls, (2) the channel aspect ratio and (3) the composite roughness on the shear stress distribution in straight prismatic channels is analysed directly based on the CFD predictions.

In wide open channels the lines of boil, consisting of low speed streaks, periodically in the transverse direction, is believed to be due to the initiation of sand ridges on the bed; in other words due to the coupled interaction between moving bed and flow. A numerical analysis on the flow structures created and the distribution of shear stresses on the bed and sidewalls of channel sections having ridges on its bed is therefore carried out to clarify this point and assess the potential consequences on our predictions.

Finally, because of obvious practical relevance, as most rivers follow a winding course, numerical simulations on the distribution of shear on the boundaries inside a channel bend is also presented.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Morvan, H.P.
Hargreaves, D.
Keywords: Computational fluid dynamics, computational fluid dynamics, Channels (Hydraulic engineering)
Subjects: T Technology > TA Engineering (General). Civil engineering (General) > TA 357 Fluid mechanics
Faculties/Schools: UK Campuses > Faculty of Engineering > Department of Civil Engineering
Item ID: 13006
Depositing User: EP, Services
Date Deposited: 03 Jan 2013 13:59
Last Modified: 14 Sep 2016 20:26

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