Study On Flow And Sediment Movement Of Bifurcation Area And Related Application Of 3-D Numerical Flow Model

The bifurcated flow, a common morphology of flow motion, usually occurs in natural rivers and headrace open channels etc. Controlled by its boundary, the bifurcated flow is complicated in structure and specialized in river evolution. Some related problems of the bifurcated flow have been researched by using theoretical analysis, diversion channel experiment and numerical modeling in this dissertation. The main contents are summarized as follows:(1) The significance of studying the bifurcated flow has been indicated. The complexity of bifurcated flow has been pointed out. Reviews of the related research on this stream have been given, including the cause of the bifurcation current, the flow motion, the sediment movement and the evolution law of bifurcation area as well as the progress of the numerical modeling and its application in the current calculation of this flow.(2) Predictive models of the diversion ratio of the bifurcation area have been established by using the equivalent value method of water level difference, the momentum balance method, the equivalent sediment-load method and the artificial neural network model. The equivalent value method of water level difference is based on the equivalence of water level difference of each branching stream, while the momentum balance method based on the principle of momentum balance in the bifurcated mouth, the equivalent sediment-load method based on the equivalence of sediment concentration in each branching stream and the artificial neural network model based on the principle of "Black Box" . Every model has example to prove its feasibility and accuracy.(3) Flow and sediment diversion tests have been carried out in the bifurcation channel. The flow and the sediment movement have been studied. The flow structure of the bifurcation area have been measured by using ADV. Researches have been made on the sediment diversion ratio experiments. The general relationship between sediment diversion ratio and every related factor including diversion ratio, the ratio of channel width to channel depth and the sand grain has been gained.(4) The generating technologies of curvilinear grid have been explored and two new methods have been presented including waiting-function method and depth-weighted function method. The influence of water depth on curvilinear grid is considered in the depth-weighted function method. The grids can be densified locally where the flow is complicated for the sharp change of water depth.(5) 2-D hydrodynamic equations in the generalized curvilinear coordinates have been derived with the contravariant velocities as main variables. The new equations keep the original styles and physical meanings. Based on the water depth correction method, the 2-D flow numerical model has been established and validated by the measured data. Using the model, the 2-D plane flows in different bifurcated channels have been simulated. The results are used to analyze the influences of the ratio of channel width to channel depth, diversion angle to the 2-D plane structure of bifurcated flow.(6) 3-D hydrodynamic equations have been derived with the contravariant velocities as main variables as well as the above 2-D model. The new forms of the hydrodynamic equations adopt the generalized curvilinear coordinates system in plane and the σ coordinate system in vertical direction. The original structures and physical meanings were kept in the new equations. The SIMPLEC method has been applied to solute the 3-Dequations. Validated by the measured data, the three dimensional numerical model is used to simulate and analyze the 3-D hydrodynamic structure of the bifurcated mouth in different boundary conditions. The results show that the flow near the bottom is more complicated than that near the surface and there is circulation current in the bifurcated mouth. The effect of the diversion angle to diversion plane in the range of large diversion angle is more effective than that in the small. The characteristic of three dimensional becomes weak with the increasing of the ratio of wi...