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Three-dimensional numerical and physical modelling of coastal hydro-environments: turbulent stratified flows in estuarine harbours and barrages

Hejazi, Kourosh 2017. Three-dimensional numerical and physical modelling of coastal hydro-environments: turbulent stratified flows in estuarine harbours and barrages. PhD Thesis, Cardiff University.
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An arbitrary Lagrangian-Eulerian (ALE) three-dimensional hydrodynamic free-surface numerical model has been developed based on the time-dependent Reynolds-averaged Navier-Stokes (RANS) equations and the finite volume method (FVM). The model with non-hydrostatic pressure distribution and a structured nonorthogonal curvilinear staggered mesh is capable of simulating non-homogeneous stratified flows and problems involving complex bathymetry. A projection method is deployed for solving the set of the equations, and a buoyant k-ε turbulence model is included in the numerical model. Six new advection schemes are introduced, and a fifth-order-accurate upstream scheme was utilised in the numerical model. Extensive numerical tests showed the capability of the model in simulating free surface flows and non-linear terms in Navier-Stokes equations. To achieve a better understanding of hydrodynamics, mixing, and salt transport and stratification and their interactive mechanisms in estuarine harbours and barrages, a laboratory tidal basin was designed, set up and employed for velocity, water surface elevation and salinity measurements of an idealised vertically distorted model harbour. For despiking and denoising the velocity data a linear algorithm was established, which successfully lowered the noise level and removed the spikes. The measurements showed a horizontal circulation in the harbour and weak vertical circulations. The salinity suppressed the circulation across the water depth, resulting in less mixing in vertical direction and stronger flushing on the surface. Comparisons of the numerical model simulations against the experimental data showed that the velocities and flow patterns were in generally good agreement with the measured values. For the fresh water the model under-predicted the dominant velocity components for the areas with strong circulation and for the saline water the simulated results showed an overprediction in lower layers and good agreements with the measured values for the top layer. The water elevations exhibited very close predictions compared with the measured data. The salinity simulated profiles showed good agreements with the measured values for lower layers and an over-prediction for the top layer. The investigations showed that the dominant velocities inside the harbour were increased for taller barriers, but with the increase of mean water depth the circulations weakened. The saline water flushing into the harbour flows underneath the fresh ambient water resulting in higher salinity concentration in the harbour over time.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Turbulent Stratified Flows; 3D Free Surface Numerical Model; Estuarine Harbours and Barrages; Harbour Physical Model; Denoising and Despiking; Finite Volume Method; Projection Method; Aribtrary Lagrangian-Elerian (ALE).
Date of First Compliant Deposit: 6 September 2017
Last Modified: 12 Nov 2021 14:04

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