Modelling of flows through hydraulic structures and interaction with sediment
arxiv: Physics::Fluid Dynamics
A three-dimensional layer integrated morphodynamic model has been developed to predict the hydrodynamic, sediment transport and morphological processes in a regulated reservoir. The model was based on an existing sediment transport model, with improvements being made. A bed evolution module based on the mass balance equation has been developed to determine the bed level change due to sediment transport. The horizontal eddy viscosity coefficient was equated to the depth averaged eddy viscosity, based on the horizontal velocity distribution while the vertical eddy viscosity coefficient was evaluated using the layer integrated form of the - equations. This scheme enhances the accuracy of the computed velocity and suspended sediment concentration distributions.\ud The highly accurate ULTIMATE QUICKEST scheme was used to represent the advective terms in solving the advective-diffusion equation for suspended sediment transport. An explicit finite difference scheme has been developed for the bed sediment mass balance equation to calculate bed level changes. The numerical model was verified against laboratory data obtained from experiments in a trench and a partially closed channel.\ud A physical model was constructed to represent the flow, sediment transport and morphodynamic processes in Hamidieh regulated reservoir. The physical model was designed based on the Froude similarity law and was undistorted. The model sediment size was determined in such a manner that the same ratio of particle fall velocity to shear velocity is maintained for both the model and prototype reservoir. Stokes law was used in calculating the particle fall velocity. The physical model results confirmed that the normal water surface elevation in the reservoir should increase by up to 25 cm in order to reach the nominal flow discharge diverted to the intakes.\ud The numerical model was then applied to the scaled physical model of the reservoir and the associated water intakes and sluice gates. Various scenarios were tested to investigate the effects of different situations of diverting flow and sediment transport regimes, as well as to establish how these operations affect the morphodynamic processes in the reservoir and the vicinity of hydraulic structures. The model predictions agreed with measured data generally well. The numerical model results revealed the possibility of forming sedimentary islands in the regulated reservoir and it is uneconomical to set up a dredging zone near the one of the intakes. In summary, the integrated numerical and physical modelling approach showed many benefits and could help to optimize time and budget for design hydraulic structures.\ud Key words: morphodynamic numerical model, turbulent flow, regulated reservoir, three- dimensional flow, laboratory tests.
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