Research On The Cavitation Characteristics Of Pump Turbine Under The Influence Of Environmental Factors

The problem of pump turbine stability has become a key issue which needs to be paid more attention to,especially the vibration and noise of the unit caused by the cavitation of the blade and cavitating vortices in the guide-stay vanes,which is one of the important factors affecting the stable operation of the unit.Especially,for pumped-storage power stations in high altitude and alpine regions,temperature and atmospheric pressure changes have an important impact on the cavitation and stability of the unit.In order to solve above problems,this paper aims to explore the cavitation characteristics in the runner,the mechanism of cavitating vortices in the guide-stay vanes and the influence of environmental factors to the cavitation characteristics of unit.The results of the above researches provide theoretical basis for improving cavitation characteristics of pump turbine and solving the long-term stable operation problem of the unit in high alpine and high altitude areas,which have important engineering application values for the safe and stable operation of pump turbine.Related conclusions are as follows:(1)Numerical and experimental study on cavitation performance of pump working condition.The results of numerical simulation are consistent with the results of the cavitation test,which can better simulate the development process of the cavitation in the runner.When Q<Q_r,the cavitation position first occurs on the back of the blade inlet;when Q>Qr,the cavitation position first occurs on the front of the blade inlet.With the decrease of the cavitation coefficient and the influence of centrifugal force of the runner,the cavitation in the runner at large flow condition is serious,and a large number of bubbles block the flow passage,affecting the distribution of the surface load of the blade,and increasing the hydraulic loss in the runner.(2)The cavitation vortices phenomenon occurred in the guide-stay vanes at the pump working condition is studied.It is found that,as the cavitation coefficient decreases,the intensity of rotating stall vortex in the guide-stay vanes gradually increase,forming cavitation vortices.The cavitation vortices mainly occurs in the stay-guide vanes domain where is close to the nasal tip of spiral case.Under the action of the reverse diffusion of the water flow,it extends into the adjacent stay-guide vanes.The cavitation vortices can cause the guide apparatus to generate low frequency and high amplitude torque fluctuations.As the cavitation coefficient decreases,the pressure pulsation amplitude increases in the vaneless zone,but the pressure pulsation amplitude in the guide-stay vanes and the runner is reduced.(3)Considering the environmental factors,the cavitation flow calculation is carried out aiming to explore these influence on cavitation characteristics of high-head pump turbine.Under the turbine operating conditions,comparing to atmospheric pressure change,temperature has a greater impact on the cavitation performance of the turbine operating conditions.Under the pump operating conditions,the lowering of the temperature increases the turbulent energy of the water flow in the runner.Considering comprehensively the temperature change and atmospheric pressure change,the temperature and atmospheric pressure are reduced,the runner blade load is reduced,the runner cavitation performance is degraded,and the cavitation performance of the pump operating conditions is mainly affected by atmospheric pressure.