Cavitation Characteristics Of Pump Turbine In High Head Pumped Storage Power Station

The pump turbine in high head pumped storage power station, which runs a large variation range of head and flow. When the water flow through the runner blade, the flow speed is high, and the operation condition of the unit is more and more complicated. Pump turbine is more likely to cavitation than conventional turbine. The cavitation flow phenomena even decrease the performance of units and causes insatiably noise and vibration when it goes worse. The pump turbine runner model of a pumped storage power station is taken as the research object. Using CFX software to analyze the pump turbine runner at different head and flow rate. Get the pressure distribution on front and back blade and cavitation prediction result under different working conditions. And put forward suggestions on the unit operation condition and the runner repair.Main work includes the following parts:First of all, build the full channel model and mesh for the pump turbine, and illustrate the grid independence. Using the CFX software to set boundary conditions, and the steady numerical simulation of turbine was carried out. The numerical results show that the cavitation of hydraulic turbine mainly occurs at the exit edge of the suction side of runner blade near the lower ring and the exit edge of the pressure side of the blade and the drafttube. The cavitation condition with the increase in the guide vane opening will become more and more serious. With the increase of the flow rate, the cavitation number of the turbine increases gradually. Under the same conditions,cavitation is more likely to occur, and the ability of the unit to resist cavitation erosion and damage is worse.Secondly, the steady numerical simulation of pump was carried out. According to the calculation results, it can be concluded that under the condition of pump, there is a low pressure zone in the suction side of the blade at the small flow condition. With the increase of flow rate, the low pressure area is transferred to the lower part of the blade. The larger the flow, the greater the area of the low pressure zone. On the blade pressure surface, the pressure distribution on the blade is uniform, and there is no low pressure area. With the increase of the flow rate, there is a low pressure area on the inlet side of the blade, and the area is also growing. On the whole, the low pressure area of the pressure surface is smaller than the suction surface. In addition, as the inlet pressure continues to decrease, there is a flow separation and vortex in the middle of the blade,which is one of the reasons for cavitation.Then, the low pressure edge angle of the pump turbine is modified and calculated. It is found that when the low pressure edge angle is 152 degrees and 156 degrees, the critical net positive suction head of the pump increases compared to the original runner, and the cavitation performance of the pump is not improved. When the low pressure edge angle is 158 degrees, the critical net positive suction head of the pump is 7.51m. Compared with the original runner, the 7.84m is reduced by 0.33m, which shows that the cavitation performance of the pump can be increased when the low pressure edge angle is increased by 4 degrees.At last, the unsteady numerical simulation is carried out for two different outlet pressure conditions of turbine. The calculation results of cavitation flow show that the cavitation volume fraction of the runner does not change with time in the case of sufficient cavitation development.The pressure fluctuation waveform of the non cavitation monitoring point is almost the same, but there is a difference in pressure. The monitoring points at the outlet side of the runner and the drafttube of the cavitation region are affected by the cavitation, which shows different characteristics of pressure pulsation. The results of pressure spectrum analysis show that the main frequency is low frequency component, which has a certain influence on the fluctuation amplitude.