Fatigue Analysis For Francis Runner Blades Based On Fluid-structural Interaction

With the development of hydropower technology,both unit capacity and structure sizeof turbines are developing in the direction of gigantism.As the core part of energy conversion for hydro-turbine,runner's dynamics property and fatigue life will greatly affect the safety and reliability of units and power grid stability.Especially some hydro-power units used as frequent adjustment in power grid and some pumped-storage pump turbine units,their blades' fatigue failure problems become increasingly serious because of runner blades' big dynamic stress caused by different frequency water pressure surge.How to predict runner blades' fatigue life based on possible working conditions and improve design feasibility in the design process,and how to extend runner's life by rationally controlling operating range in the running process become the key technical problem that turbine power generation industry urgently wants to solve.Combined with the reliability analysis for the Francis turbine runner of a high head hydropower station in capacity expansion process,this dissertation studies dynamic response properties of runner blades caused by water pressure surge,and on this basis explore the fatigue analysis method of runner blades.The specific research contents and conclusions are as follows:(1)The transient flow field numerical simulation of turbine full passage was analyzed to get water pressure data of splitter blade and study the law of water pressure surge.The results show that: Water pressure surge on the surface of splitter blades at different working conditions is obvious,and water pressure surge of short blade is stronger than long blade;the rotor-stator interaction between runner and movable vane will affect the water pressure surge,and the effect will decrease gradually through inlet edge to outlet edge of blades.(2)Based on the results of flow field numerical calculation,one-way fluid-structure interaction method was used to do the transient dynamic analysis for splitter blades to locate the critical position and get stress-time history data.The results show that: Splitter blades bear obviously alternating dynamic stress at different working conditions in one rotary cycle;the critical position of splitter blades locates at the joint between outlet edge and runner band,and its max stress will get larger with the increase of the output.(3)The influence factors of turbine runner's fatigue life were studied.The results show that: Factors like stress concentration,structure size,surface working and mean stress have some effect on splitter blades' fatigue life,and among those the mean stress has the most obvious influence.(4)Based on gained stress-time history data,structure fatigue theory was used to do the fatigue life calculation of splitter blades' critical position.The results show that: The fatigue life of splitter blades' critical position meet the normal operation requirements of the hydropower station.This dissertationshows that: Using water pressure surge analysis and dynamic analysis based on FSI to calculate turbine runner's fatigue life is a feasible technical route.This method can be used to predict fatigue life and has some engineering application value and theoretical significance.