Effect Of Flap Size On Cavitation Characteristics Of Francis Turbine Runner

Cavitation often appears when the hydraulic turbine is running,which always cause poor performance of the turbine,threaten the safe and stable operation of the unit.In order to solve the problem,this study took the francis turbine as the research obj ect and added different flaps on the basis of the original runner.Numerical calculations of cavitation performance in clean water and sandy water were carried out at small flow and design flow conditions.The results show that cavitation mainly occurs at the outlet side of the suction surface of the runner blades and will be more serious with the promotion of sediment particles When the water contains sediment.It is evident that the vapour volume fraction decreases and the streamline is smoother when adding flaps on the original runner because flaps divert the incoming flow from the runner inlet and increase the cascade solidity,the flow velocity and sediment velocity are reduced,which will lessen the abrasion on runner blade and optimize the cavitation performance.On the one hand,the article researches the effect of flap height on turbine performance.The flaps are 80mm length with three different heights,which are 10mm,20mm and 30mm respectively.Under small flow conditions and design conditions,the turbine efficiency and output power are maximum,the water volume fraction of suction surface and the water and sediment velocity distribution in the runner are the best when the flap height is 30mm and 10mm respectively.On another hand,the article compares the effect of flap length on turbine performance.The flaps are 10mm height with three different lengths,which are 60mm,80mm and 100mm respectively.The length of the flap has no evident effect on the energy and cavitation characteristics of the turbine.Unsteady calculation analysis of francis turbine found that the volume fraction of cavitation do not change with time.After adding flaps,the pressure fluctuation range of monitoring point of the runner outlet reduces,which is significant to the stability of the turbine.Current researches about the influence of flaps on the cavitation performance of francisCurrent researches about the influence of flaps on the cavitation performance of francis turbines are still not enough.I hope that the research in this article provides a reference for improving the cavitation performance and optimizing design of hydraulic turbine runners.