| In this article, based on reading and studying a great number of references about fluid dynamic technique, computational fluid mechanics, numerical computing methods of flow field, visualization in science computing, experimental visualization in fluid flow computer digital image processing technique etc, the mathematical models which governing the flow in complicated conduits and hydraulic valve have been derived, the finite element method is applied to simulate the flow field of various non-circular cross- section duct, various complicated channel and hydraulic valve, the computing results are given in the form of visualized pictures or images, based on these results, the relationship between the flow field structure and the flow noise, energy loss are analyzed quantitatively. At the same time, the experimental visualization - DPIV(Digital Particle Image Velocimetry) is also carried out, and it proves the computing result is correct. It has important significance for us to design hydraulic valves and pipeline systems which are high in efficiency, low in energy loss, low in noise. In chapter 1, hydraulic technique and its developing trends are summarized, the flow problems in complicated flow channel of hydraulic technique are introduced. Various numerical methods of computational fluid dynamics are present briefly, the present situations of application of computational fluid dynamics in hydraulic technique are described in detail. The computational visualization technique of flow field is outlined, various flow field experimental visualization methods are surveyed. The application of computer digital image processing technique in experimental visualization of flow field is discussed. The main researching contents are determined. In chapter 2, the mathematical model which governs the flow in non-circular cross- section channel is established, FEM(Finite Element Method)is used to discrete the equations. The cross-section parameters such as velocity and flowrate at different flow conditions for various non-circular duct such as equilateral triangle channel, rectangle channel, terrace channel, semi-elliptical channel etc are calculated. Parts of the numerical results are compared with the analytical results, it shows that the numerical method used here is correct. In chapter 3, several different kinds of mathematical models and their characteristics when we solve the flow problems with FEM are presented. From continuity equation and Navier-Stokes equation, non-dirnensionalized stream function ?vorticity equations is derived. Ho~v to analyze the elements with FEM and how to calculated the related coefficients when adopting three nodes triangle elements and four nodes quadrilateral elements respectively is proposed, which is the key for computing the flow field correctly. In chapter 4, how to determine the boundary conditions of stream function and vorticity, especially vorticity boundary conditions at inlet, outlet, up wall, down wall and the corner are studied when using FEM to solve the stream function-vorticity equation. Several approaches of determining the vorticity boundary condition are discussed. The flow in parallel plate channel is computed as an example to verify their accuracy. Based on above analysis, the flow in square cavity and backward-facing step is investigated, the influence of inlet and outlet boundary conditions on backward facing step are also examed. In chapter 5, the flow field of several different flow channels frequently used in hydraulic technique such as sudden expansion channel, sudden contraction channel,...
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