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Large Eddy Simulation of flow around bridge abutments

Chua, Ken 2018. Large Eddy Simulation of flow around bridge abutments. PhD Thesis, Cardiff University.
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Abstract

Extreme hydrological events have increased the frequency of ooding scenarios in recent years, resulting in significant bridge inundation and associated damages. Turbulence structures within the ow field are highly energetic and possess high sediment entrainment capacity which will lead to the scour formation around the bridge foundation and consequently causes structural instability or even failure of the structure. This research employs the method of Large Eddy Simulation (LES) to elucidate the complex ow mechanisms around bridge abutments in changing conditions. The level set method (LSM) is adopted in LES code to predict the complex water surface profiles and an extensive validation of the method against complementary experiment is presented. A faithful representation of a natural river which consists of an asymmetrical compound channel with a parabolic main channel and two variable-length abutments with sloped sidewalls and rounded corners, and a bridge deck is presented in this thesis. The LES code is used to analyse the effect of bridge abutment length on the turbulence structure and ow field through the bridge opening. Extensive analysis by means of streamwise velocity contours, 2D and 3D streamlines, isosurfaces of Q-criterion, contours of wall-normal vorticity, probability density functions, quadrant analysis, power density spectra, and water surface elevation contours has been carried out and have shown significant differences between the different abutment lengths. The findings attempt to contribute to the design of resilient hydraulic structures especially on considering the shape and size of an abutment. The investigation of ow mechanisms around bridge abutments under different scour conditions (i.e. pre-scour and equilibrium scour) is presented in the later part of the thesis. Through 3D streamlines and contours of vertical velocity and turbulent kinetic energy, the equilibrium scour case reveals an increase in the three-dimensionality of the ow around the left abutment in the scour region when compared with the at bed case. Focusing on the near bed quantities, i.e. bed shear stress and near bed turbulent kinetic energy, the equilibrium scour case shows a significant relaxation at the vicinity of the left abutment, indicating a drastic reduction in sediment activities.

Item Type: Thesis (PhD)
Date Type: Submission
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Large Eddy Simulation; Computational Fluid Dynamics; Bridge Abutment; Level Set Method; Turbulence; Abutment Scour.
Date of First Compliant Deposit: 13 November 2018
Last Modified: 13 Nov 2018 09:44
URI: http://orca.cf.ac.uk/id/eprint/116655

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