| The operational stability of Francis turbine is a worldwide difficult problem that puzzles domestic and international hydroturbine industry,especially the operational stability of Francis turbine at middle and low water head.At present,the operational stability problem of large turbine has no effect ive solutions.The factors affecting the stability of turbine are complex,and pressure pulsation problem in partial load condition is particularly prominent.Comprehensive management of Fengman Hydropower Station based on the National Development and Refo rm Commission approved the China(reconstruction)project(hereinafter referred to as the Fengman reconstruction of power plant)based on the research and development of high specific speed mixed flow turbine,mainly to solve the problem of stability of part load.According to the characteristics of Fengman power plant,based on big data analysis,CFD analysis and model test method,the paper worked on exploration of design technology to ensure hydraulic stability of low head of unit.It presented the content concerning the process solved the stability problem of Fengman reconstruction,key technology and the corresponding results,which have a real breakthrough in the new section to improve stability of low head unit.First of all,based on the statistics and analysis of the big data of field operation of Fengman old power station in recent 8 years,it is found that Fengman reconstruction power station is different from the conventional hydropower station of similar water head section,which has special water regime,electricity condition and operation characteristics.The key parameters of hydraulic performance,specific speed and suction height are demonstrated and analyzed.The key points and difficulties of project development are identified.The key para meters of hydraulic development of hydraulic turbine are put forward.At the same time,through the model test of variable cavitation pressure pulsation,it is verified that the installation elevation is reduced,and the amplitude of pressure pulsation of some working conditions is reduced remarkably.Secondly,this thesis focuses on the research of the runner which has great influence on the stability of the hydraulic turbine.The important influence of runner design on hydraulic stability is expounded from several aspects,such as runner design method,design stage and key parameters of runner.The results show that the new blade meridian plane and the number of blades increaded can extend the efficiency hill chart to the horizontal that will have a higher efficiency and wider operating range.Also,the crowns of the blade and inlet edge have obvious influence on the vortex in blade passage which was verified by model experiment.Finally,by using the method of CFD numerical simulation method and experimental combination,focusing on different cones the conical tube flow were observed and analyzed.The result shows that the variation of cone shape on the flow of internal pressure field,pressure gradient,pressure pulsation effects are obvious.Suitable cone will significantly change the location,shape and frequency of vortex,reduce the pressure fluctuation energy or other specific frequency energy,and improve the system stability.This thesis has certain guidance and reference for key technology of low head Francis turbine hydraulic stability,the new design ideas and methods can be applied in other power plants and provide engineering reference method for reducing the partial load pressure fluctuation. |
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