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Effect of Diameter of Guide Vane Distribution Circle on Pressure Fluctuation in Vaneless Zone of Francis Turbine
Author(s): zijuan wu, Wuke Liang, W. Dong
Keywords: Francis turbine; Guide vane; Distribution circle diameter; Vaneless zone; Pressure fluctuation
In a Francis turbine, the guide vanes are arranged in the direction of flow after the stay vanes. It is generally believed that the outlet angle of water after it flows through the volute and stay vanes is fixed. Flow and flow circulation are adjusted by changing the opening of the guide vanes so as to adjust the output of the turbine. The dynamic-static interference effect induced by the interaction between the guide vanes and the runner of the Francis turbine was one of the main causes of the pressure fluctuation. The effect of guide vanes placement on pressure fluctuation in vaneless zone of Francis turbine was studied. In this study, the commercial software ANSYS CFX16.0 was used for the three-dimensional numerical simulation of the whole flow passage of a Francis turbine model in a power station. The turbulence model used in the calculation was the shear stress transport (SST) model. The independence between the total number of computational meshes and the timestep was verified to ensure the reliability of the calculation results. Five schemes with different diameters of the guide vane distribution circle were proposed, with D0/D1 (diameter of guide vanes/diameter of runner inlet) equal to 1.119, 1.128, 1.138, 1.144, and 1.15. Twenty monitoring points were set up in the vaneless zone between the guide vanes and the runner to collect pressure fluctuation signals in the vaneless zone. By analyzing the characteristics of unsteady pressure fluctuations in the vaneless zone under design conditions of the five schemes, the optimal position of the guide vanes was determined. The numerical results showed that the pressure fluctuation amplitude at monitoring points in the same axial direction increased gradually from the top cover to the bottom ring. When the unit operated under the design conditions, by increasing the diameter of the guide vane distribution circle, the dynamic-static interference between the guide vanes and the runner domain was weakened, and the pressure fluctuation amplitude in the vaneless zone between the guide vanes and the runner was reduced, thereby improving the stability of unit operation.