Research On Typical Pressure Balance Method Of Francis Turbine Runner With Low Specific Speed

The most prominent geometric features of francis turbine runner with low specific speed is that the radial portion of the runner has a large proportion,it is easy to form a large pressure difference in upper crown runner and lower ring runner,causing axial water thrust imbalance,push-up or burnt tile etc,and iMpacting on safe and stable operation of the unit.Such phenomena have occurred in some domestic hydropower station units.Gradually,more and more huge unit size of francis turbine runner with low specific speed is puting into production,the design and operation of water heads is continuing to improve,and the traditional turbine runner pressure balance method can no longer meet the current demand,therefore,the special research on the new pressure balance technology has great significance.The project is based on a domestic hydropower station which design head is around700 m.The relationship between the main technical parameters corresponding to different and typical pressure balance method and the operating conditions of the turbine was analyzed,and the law of change was drew.The targeted analysis of the "gap pressure balance method" was done,and the project reference opinions was proposed.The theoretical quantitative research of the "pressure balance tube" was done,and its rationality is discussed.Must point out,public reports or references on the research results of runner pressure balance technology are quite limited at home and abroad,especially,pressure balance tube technology has not been successfully designed or used in China.So,the research results of this subject has great value in theory and in practice.Under the premise of considering the special cases of the Hydropower Station,the project borrowed basic theory based on engineering fluid dynamics and computational fluid dynamics,divided the research into multiple stages,the research objectives,methods and results of each stage complement each other.Research results focus on axial water thrust,gap leakage and volumetric efficiency etc.In the first stage,the gap pressure balance method was studied in detail,determined the beneficial gap size.The second to fourth stages studied whether the pressure balance tube be useful,firstly,the design rationality of the internal pressure balance tube was verified,secondly,the design feasibility of the external pressurebalance tube was discussed.Special explanations were given on key and difficult issues such as vortex,sealing structure and leakage amount determination method,in particular,the original "indirect calculation method of boundary conditions" solved the problem of calculation accuracy to a great extent.The adoption of the pressure balance tube technology needs to be based on the actual situation of the hydropower station unit,many factors should be considered during the design phase,its a relatively complex comprehensive problem.The research results of the new pressure balance technology may not be perfect enough,but technical experience needs to accumulate,it also takes time to transform results,industry development requires scientific and technical personnel to master various pressure balance method of francis turbine runner.In addition,this paper only covers technical and program verification,the specific design details are not disclosed without the authorization of the cooperation.