| Shaft-extension type tubular turbine is a major type for developing medium and small-sized low-head hydropower station. The three-dimensional flow field in draft tube is complex, which has large influence on energy characteristic and stabilization of water turbine. Using CFD to calculate the flow of draft tube through three- dimensional numerical simulation, it can simulate and predict flow characteristic, optimize the type and dimension of draft tube, improve the efficiency of turbine and the stabilization of operating. It also has value in theory and application.The geometrical model of draft tube was made by Pro/E, a three-dimensional model building software. Taking FLUENT software as numerical simulation platform, the flow field in draft tube was determined. A scheme was used in this paper with Reynolds-Averaged Navier-Stokes equation and standard k-ε turbulence model. The computing zone was meshed by unstructured grids. The boundary condition included velocity inlet and outflow in outlet. The control equations were treated with by finite volume scheme, second-order upwind scheme and made a discretization using SIMPLEC algorithm which has good convergence for pressure and velocity. Through three-dimensional numerical simulation of flow field in draft tube of shaft-extension type tubular turbine, the following conclusions can be drawn.1. Using Pro/E to make the geometrical model is feasible and convenient.2. Unstructured grids used in calculation can satisfy the calculation requirement of complex flow in draft tube, which has strong adaptability.3. Defined parameters were appropriate, which can reflect main flow in draft tube. It also instructed that the calculation was correct.4. Through three-dimensional numerical simulation of water field in draft tube, it can show the velocity and pressure distribution in draft tube, which is helpful to optimize parameters in designing hydropower station and draft tube. It also has important meaning for optimum design of hydropower station.
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