Study On Working Characteristics Of Pump-plate Structure And Head-cover Water Supply Mechanism Of The Francis Turbine

Francis turbine head-cover water supply(HCWS)as a method of technical water supply is gradually popularized. HCWS is using non-power leakage water that among the head cover wearing ring and runner wearing ring as the water source of technical water supply. It has the characteristics of energy saving and environmental protection. It is also clean, safe and reliable. Under current technical conditions, there are two types of HCWS structures. One is designed with a pump-plate and another has no pump-plate structure. The structural design will directly affect the effect of the HCWS and the safety of the unit. At present, the quantitative research on the structure of the HCWS system is seldom. There is no reliable theoretical basis during the designing process. Therefore, it is of great significance to study the working characteristics of the HCWS structure.The technical proposal of the HCWS is going to be used both on Miaowei and Huangdeng hydropower station. This subject uses the HCWS system of the two hydropower stations as the research object. We study the influence of the HCWS structure on the performance of the technical water supply. Establish three-dimensional models for various of HCWS structures. Using numerical simulation method to mesh different computational domains and select appropriate boundary conditions for calculation based on actual working conditions. We compare and analyze the working characteristics of the HCWS schemes based on the numerical simulation results. And then obtains the hydraulic model with the best performance.This paper focuses on three aspects of the research work. First of all, based on existing experience of HCWS, the CFD numerical simulation calculation and analysis was carried out aiming at a HCWS structure that the pump-plates are radially arranged and two common HCWS structures without pump-plate. In this thesis, we Focus on three indicators of the water intake pressure for HCWS, the crown axial water thrust and the power dissipation of pump plate. We analyze the internal flow between the Head-cover and the Crown, study the effect of pump-plate in the structure of the HCWS and the respective advantages and disadvantages of the HCWS structures involved in this subject. Then provide the theoretical basis for the designing of the HCWS structure.Secondly, according to the technical water supply requirements of the Miaowei and Huangdeng hydropower station unit and the characteristics of hydraulic turbine structure, having studied the impact of pump-plate structure about different slant angles and sealing radius to the HCWS. Same as above, regard the water intake pressure for HCWS, the crown axial water thrust and the power dissipation of pump plate as the performance index. Flow characteristics analysis was carried out on different schemes of slant angles of the pump-plate structure under several conditions. Different structural forms of the pump-plate has different effect on the water intake pressure for HCWS, the crown axial water thrust and the power dissipation of pump plate. It is feasible to explore the most conducive angle of inclination to improve the performance of the HCWS through comparison and analysis. On this basis, according to the design radius R of the pump-plate sealing radius offered by the design party, we increase and decrease the pump-plate sealing radius along the radial direction. Set a number of control group, which were calculated and compared in the same conditions. And find out the effect of pump-plate sealing position on the performance of the HCWS to lay foundations for the design of the HCWS structure.At last, considering the situation that there will be an enlargement on the sealing clearance after a long-time working of the runner, in this thesis, we carry out numerical analysis on three models: the original size of the clearance, the clearance width increased by 0.5mm and the clearance width increased by 1mm. Then study the relationship between the clearance width and the leakage, the crown axial water thrust and the power dissipation of pump plate. This is of great significance to the safety and stability of the hydraulic turbine in the later stage.