Abstract
The rotating stall is an unstable flow phenomenon of pump turbines in pump mode, which is of increasing concern to scientists and engineers working on pump turbines. However, at present, various studies are carried out based on CFD (computational fluid dynamics) simulation, while directly measured data and experimental research on flow fields are seldom reported. By utilizing PIV (particle image velocimetry) measuring equipment, the flow field within the guide vane zone of a low specific speed pump turbine in pump mode was measured. By measuring and analyzing the transient flow field, the evolutionary process of the rotating stall within the guide vane passages was determined. We found that for all three tested guide vane openings, regardless of whether the positive slope appeared or not, a pre-stall operating point was found for each opening in the process of decreasing the flow rate. The analysis of the loss within the flow field indicated that the dissipation-induced loss increased greatly after the rotating stall appeared. The pump performance curves at the three guide vane openings showed an inflection at the pre-stall point. When the flow rate is larger than that of the pre-stall point, the head of the pump turbine dramatically increases as the flow rate decreases. However, when the flow rate is smaller than the pre-stall point, such increases noticeably slows down. The research results showed that whether the positive slope on the pump performance curve occurred or not, instability caused by the rotating stall should be of great concern.
Highlights
Large-scale pumped storage power (PSP) plants generally undertake more responsibility for load-levelling, frequency regulation and stabilization of the power grid
One of the main unstable flow phenomena of a pump turbine operating in pump mode is the rotating stall
The accuracy of the particle image velocimetry (PIV) data of this experiment is 2%~4% according to Raffel [32] and the main focus of the present study is on the detection of large-scale structures during the rotating stall
Summary
Large-scale pumped storage power (PSP) plants generally undertake more responsibility for load-levelling, frequency regulation and stabilization of the power grid. The simulation result revealed the process of great fluctuation of the flow rate in the guide vane channels and corresponding evolutionary process of flow fields They concluded that the occurrence of the rotating stall causes the reduction of the heads in the hump-shaped region. Compared to the previous studies, all the stay vanes were retained so that the flow passage of the measured pump turbine model met the geometrical similarity requirements of the International Electrotechnical Commission (IEC) standard [30] Based on these conditions, systematic PIV measurements were performed on the flow fields around guide vanes of a pump turbine model on the high-precision model test platform. This study further facilitates the optimization design of pump turbines and operation stabilization of PSP
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