| Water resources in China ranks first in the world, the development and utilization of water resources has been a major issue. Under the background of the priority to develop hydropower, the development of Chinese hydropower construction is extremely enhanced. Corresponds to the trends of large capacity, high water head, high specific speed of hydraulic turbine, new requirements for the design, manufacture and scientific research of hydraulic units are needed.Three indicators which affect the performance of hydraulic turbine units are efficiency, stability and cavitation performance. Currently, the maximum efficiency of hydraulic turbine can reach95%, while cavitations problem was an ancient issue and the instability of hydraulic turbine also gradually revealed with the improvement of the capacity and water head. During the operation of hydraulic turbine, cavitations will make flow components damaged by cavitation, resulting in noise and vibration which seriously affect the efficiency and stability of hydraulic units. Therefore, the cavitation of hydraulic turbine become one of the fundamental problems which people are very concerned about in the field of hydraulic turbine. Runner is the core flow component of hydraulic turbine, it plays a decisive role in the performance of the hydraulic turbine. Accordingly, the study of turbine cavitation problem should be more attention, and it must be carefully investigated to improve the performance of the hydraulic turbine.With the development of CFD and the technology of computer, numerical simulation has become an important way to investigate internal flow of hydraulic turbine. There is a significant meaning for improving the stability and economical operation of hydraulic turbine through analyzing and designing with the help of low-cost, short-cycle numerical simulation.Based on computational fluid dynamics, the versatility CFD software called FLUENT is used in this paper to simulate the single-phase three-dimensional turbulence of internal flow of Francis turbine runner with attached blades. In the simulation, RNG κ-ε two-equation turbulence model is utilized which is based on Reynolds averaging method, according to simulation results, the three-dimensional flow field distribution of turbine runner in different operating conditions can be obtained, and then the calculation results of single-phase flow are utilized as initial values which supply the no-slip two-phase fluid mixture model, and then the internal cavitation flow of the turbine runner can be simulated. Based on simulation results, cavitation flow field distribution of this type of turbine runner under different flow conditions can be obtained. Calculation results can be used as reference for predicting and improving the cavitations performance of hydraulic turbine.The results also play important role in improving efficiency, stability and overall performance of the hydraulic turbine. The specific jobs in this paper have been done as follows:1. According to design parameters of the Francis turbine with attached blades HLA351, three-dimensional geometric model of runner of this type of hydraulic turbine is established by using solid modeling tools called Pro/ENGINEER software. And then the pre-processing tools called GAMBIT is used to finish the work such as meshing for geometric model of the runner, setting boundary type, etc. Thus, a physical object which can be used CFD calculations is successfully established.2. Using simulation tools called FLUENT to simulate the internal single-phase flow field for Francis turbine runner with attached blades, and then three-dimensional flow field distribution in different operating conditions can be obtained.3. The calculation results of single-phase flow are used as initial values which supply the no-slip two-phase fluid mixture model to simulate the internal cavitations flow of the turbine runner. Cavitation flow field distribution of this type of turbine runner under different flow conditions can be obtained finally.4. After the calculation, the calculation results of single-phase flow and cavitations flow are investigated. According to investigation results, the cavitations flow in this type of turbine under different operating conditions is summarized and analyzed.
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