The Relationship Of Flow Characteristics And Working Condition In The Runner Gap Of Francis Turbine

There is an empty cavity between the runner crown and head cover in Francis turbine,some of water will flow into the sealing clearance of the runner crown,finally leak out to the empty cavity when the hydro-turbine is working.The leakage water not only give rise to the volume loss of the hydro-turbine,but also cause an axial hydro-thrust which direction is in accordance with the principal axis of runner.With the development of increasing diameter and unit capacity of runner,large Francis turbine has a larger carrying area and water pressure in runner crown,which lead to a larger axial hydro-thrust and causing negative effects to stable operation of the unit,causing accident such as thrust tile burning,seriously restrict the design of thrust bearing.Because of the closely related of the structure and internal flow characteristics in runner crown,it is difficult to reliable calculate and analysis by traditional experience methods,therefore,the structure design of water release and pressure reduction is a quite important subject in the industry at present.With the development of CFD numerical simulation technology in internal flow simulation of turbomachine,numerical simulation technology has become the important method of gap-flow research in turbomachine.This paper is based on the subject which is provided by Dongfang Electric Group limited company,mainly on the basis of the structure of water release and pressure reduction in Guli hydroelectric power station,adopt the method of numerical simulation analysis,mainly completed the following three aspects of research work.The Francis turbine of Guli hydroelectric power station has two solutions in the structure of water release and pressure reduction.This subject firstly using numerical simulation technology to analysis the internal flow aim at the two different solutions of water release and pressure reduction,comparative study the difference of the relative gap leakage and axial hydro-thrust in the runner crown,choosing a recommended solution which has smaller axial hydro-thrust when the volume loss is in a reasonable range.Secondly,this paper using the solution of Guli hydroelectric power station as prototype solution,to test and verify the necessity of relief-plate in hydro-turbine,studying the difference of relative gap leakage and axial hydro-thrust in the cavity of the runner crown when the relief-plate structure is different.At last,for the problem of increases in gap size,which caused by water scour and sand abrasion after the hydro-turbine working a long time.This paper using the solution of Guli hydroelectric power station as prototype solution,design five gradually varied solutions of gap size to compare and analysis,to study the influence of gap size to relative gap leakage and axial hydro-thrust,to provide theoretical foundations to the stable operation and maintain of hydro-turbine in the later stage.