Study On Three-Dimensional Hydrodynamic Model With Curvature Correction In Curvilinear Coordinates

The prediction of flow and sediment transport is one of the most important tasks in river engineering and related areas. With the development of industry, a large amount of industry waste water and life polluted water harmful to people and other living things is discharged into river, lake, reservoir and ocean and make the natural water much more polluted. To protect environment, people must study the hydrodynamic and pollutant transport characteristics to obtain the distribution of the concentration.The prediction is very difficult because the flow in open channels is usually turbulent, the geometry is irregular and can vary with time, and sediment transport phenomena are very complex. Until now, predictions of flow and sediment transport in rivers usually neglect the influence of secondary flows. However, this influence is important for the main flow and the sediment transport and can only be accounted for realistically with a 3D model.In this paper, a 2D depth-averaged model for simulating and examining flow patterns in channel bends has been proposed, which takes into account the influence of the secondary flow phenomenon through the calculation of the dispersion stresses arisen from the integration of the products of the discrepancy between the mean and the true velocity distributions. And a three-dimensional numerical hydrodynamic model with an orthogonal curvilinear coordinate in the horizontal direction and sigma coordinate in the vertical direction has been developed, and the model includes the effects of significant curvature. The two models can effectively solve the practical problems of flows and water quality transportations in hydraulic engineering, and can strengthen the practical usage of the mathematical model. The research also has theoretical meanings and practical values in engineering.The research details and results of this paper are as follows:1. The purpose and meanings of the research has been discussed; the development of numerical simulation for flows and matter transportations have been analyzed and commenced, and the problem to be solved has been presented; the update turbulent theory, numerical method and the key techniques in turbulence numerical simulation (such as the discretization method, the method of determining free water surface, and treatment of complicated boundary, etc.) have been summarized. 2. A new method for the generation of curvilinear grid has been proposed. Some curvilinear grid generation examples show that satisfactory grids can be generated for simple-connected regions and connected-regions with complex boundary by using the proposed adjusting factors. The curvilinear grid at boundaries is orthogonal and the interior grids can be adaptive to the variation of physical parameters of fluid.3. A 2D depth-averaged model for simulating and examining flow patterns in channel bends has been proposed. In particular, this proposed 2D depth-averaged model takes into account the influence of the secondary flow phenomenon through the calculation of the dispersion stresses arisen from the integration of the products of the discrepancy between the mean and the true velocity distributions. The proposed model uses an orthogonal curvilinear coordinate system to efficiently and accurately simulate the flow field with irregular boundaries. Two sets of experimental data were used to demonstrate the model's capabilities. The simulations considering the secondary flow effect agree well with the measured data. Furthermore, an examination of the dispersion stress terms shows that the dispersion stresses play a major role in the transverse convection of the momentum shifting from the inner bank to the outer bank for flows in both mild and sharp bends.4. A three-dimensional numerical hydrodynamic model with an orthogonal curvilinear coordinate in the horizontal direction and sigma coordinate in the vertical direction has been developed. The use of the curvilinear coordinates and non-staggered grid system increases the ability of the presented model in computing complex 3D flows.5. To increases the ability of the present model in computing complex 3D free surface flows in channel bands, the three-dimensional hydrodynamic model in curvilinear coordinates including effects of significant curvature has been developed.6. The modified three-dimensional hydrodynamic model was used to predict the hydraulic characteristics of Three Gorge river flow when the left river is being closed and water has to pass only through the right channel.The important hydraulic parameters such as velocity and water level have been obtained very easily, and the computed results are in agreement with experimental data under different practical conditions.