Prediction Of Dynamic Stress Of Runner Of High-head Pump-turbine Caused By The Rotor-stator Interaction

The fatigue crack of the runner is a hot issue in the operation of the high-head pumpturbine,and the dynamic stress is an important reason for the fatigue crack of the runner.Due to the large variation of operating head,high speed and frequent switching between working conditions,the dynamic stress caused by fluid structure coupling is very complex.The pressure fluctuation caused by rotor-stator interaction in the vaneless space,and the dynamic stress of the runner blade caused by fluid structure coupling is one of the main reasons for the runner fatigue crack.At present,the main research method for the dynamic stress of runner is model test,which cannot find the fatigue crack of runner in advance in the stage of runner design.How to effectively predict the dynamic stress changes of the blades under different working conditions in the runner design stage according to the operating characteristics of the unit,improve the reliability of the runner design,and how to reasonably control the operating area during operation to avoid excessive dynamic stress of the runner blades caused by pressure fluctuation and the improvement of the operation stability of the unit are the key technical problems that need to be solved urgently in the design of the high-head pump turbine runner.In this paper,we combined with the study of the NSFC(code:51379179),a method for predicting the dynamic stress characteristics of the runner blade is studied with a 650 m head model high-head Francis pump turbine based on fluid-structure coupling numerical simulation,which provides technical reference for the analysis of the cause of runner fatigue crack damage during the design and operation of high-head pump turbine considering the dynamic stress design of the runner.The main research internal and conclusion are as follows:(1)Research prediction method of pressure fluctuation caused by rotor-stator interaction in a pump-turbine.The three-dimensional unsteady numerical simulation was used to analyze the pressure fluctuation characteristics of guide vane and runner.The results show that the pressure fluctuation induced by rotor-stator interaction in vaneless is the most intense.the main frequency is runner blades passing frequency,and the amplitude of the pressure fluctuation is much larger than that in the runner and the guide vane.Due to the excitation of the guide vane,the frequency component of runner is guide vane passing frequency.And due to the excitation of the runner,the frequency of pressure fluctuation in guide vane is mainly runner blades passing frequency.(2)Research prediction method of dynamic stress characteristics of the runner blade caused by rotor-stator interaction in a pump-turbine.The one-way transient fluid structure coupling method was used to analyze dynamic stress distribution law of the runner and the dynamic stress characteristics on the dangerous parts.The results show that the dynamic stress in the runner is always concentrated at the connection between the high-pressure side of blade and crown,band.The dynamic stress which from the high-pressure side to the low-pressure side of the blade decreases firstly,and then changes smoothly.The dynamic stress at the dangerous part of runner blade has a periodic change,and the number of periodic change in a rotation period is directly related to the number of guide vanes.The guide vane passing frequency is the main frequency component of the dynamic stress on the runner,which indicates that pressure fluctuation caused by rotor-stator interaction is the main reasons for change of dynamic stress of runner.(3)The modal analysis of the structure dynamic of the runner was carried out to determine whether the vibration characteristics of the runner structure and the vibration characteristics of the runner caused by rotor-stator interaction will produce hydraulic resonance.The results show that excitation frequencies caused by rotor-stator interaction are not coincident with the natural frequency of runner,and the unit can not have hydraulic resonance.The vibration mode of runner on low order is swing.In this paper,the method of predicting the dynamic stress of the runner caused by rotor-stator interaction of the high-head pump turbine based on the fluid structure coupling numerical simulation can reflect the dynamic stress characteristics of the runner caused by the pressure fluctuation caused by rotor-stator interaction.It also can be used to predict the dynamic stress characteristics of the runner of the high-head pump-turbine at the beginning of the design process and guide the optimization of the mechanical characteristics of the runner structure design,with certain engineering application value.