Research Of The Special Flow Inside The Pump Turbine During The Startup And Shutdown Process In Pump Mode

The pump turbine has a complicated working mode conversion during the operation. Thus,it's very important to guarantee the stability of the units when the working mode is alternating.Recent years, in some pumped storage power station, the vibration and abnormal sound occurs at the distributor of the pump turbine during the startup and shutdown process when the guide vane opening is very small. In order to find out the root cause of this unstable phenomenon, this paper conducted a deep research on the unstable phenomenon occurred at the small opening region during the startup and shutdown process of a pump turbine in pump mode.The pump turbine of Tian Huangping pumped storage power station was regarded as the research object in this paper, and the fully flow passage from the inlet of spiral case to the outlet of the draft tube of the prototype turbine was established. The startup process and shutdown process were analyzed by setting the transient calculation results of the power station as the boundary condition and implementing the dynamic meshing technique on the guide vane domain. Also, the formation mechanism and flowing regularities of the special flow pattern during the startup and shutdown process was analyzed quantitatively. The research indicated that the main flow between the guide vanes will deflect, between the normal flow pattern (type?) and special flow pattern (type ?), with the changing of the guide vane opening. During the startup process, when the opening is very small, the mainstream stays in type ? .With the increasing of the opening, the mainstream deflects from type ? to type?. Finally, the mainstream stays in type ? . During the shutdown process, when the opening is very large, the mainstream stays in type ?, and with the decreasing of the opening, the mainstream deflects from type ? to type ?. Finally, the mainstream stays in type ?.The deflecting opening and deflecting time of different guide vanes has little difference between each other, but they have the same trend. There also have some difference between the deflection process of the startup process and shutdown process, the deflection process experienced a long deflecting time in shutdown process, and the mainstream will swing back and forth in the process of deflection. The deflection also can lead to the sharply changing of the flow field near the guide vane, and this sharply changing results in the dramatic upheaval of the hydraulic torque of the guide vanes, then, the vibration and abnormal sound occurred. The results has a good coincidence with the operation of the units which working at the small opening region during the startup and shutdown process, and indicates the reason of the vibration occurred at the distributor of the pump turbine.In order to explain the unstable incentives of the pump turbine during the startup and shutdown process, the static stress on the guide vane during the startup and shutdown process was analyzed. The results indicated that the maximum static stress of the guide vane occurred at junction of the end face of the guide vane and the axis. Moreover, the deflecting of the mainstream can lead to the sudden change of the stress of the guide vane, caused the instability of the units.