Research and optimization of performances of a pump turbine in pump mode

Abstract

For reversible pump turbines, a sufficient hump safety margin has to be provided under small-flow and high-head conditions to avoid instability resulting from operations in the hump-shaped zone. On the other hand, under large flow conditions, cavitation easily occurs on the low-pressure edge of runner blades due to effects of low pressure and flow separation, sharply reducing the efficiency and lift head. Therefore, the hydraulic design of the pump turbine in pump mode is crucial for the properties of energy, cavitation and stability of the whole unit. A model runner (runner A) designed for a pumped storage power plant in China was demonstrated with insufficient hump safety margin and poor cavitation performance. To improve those deficiencies, optimization design was carried out on the geometric dimensions of the runner A, based on the computational fluid dynamics (CFD) analyses and model test results. The final model runner B was designed with less blade number Z and large blade wrap angle θ, to both alleviate the flow separation around the lower pressure edge of the blade and the non-uniform velocity distribution in the outlet area around high pressure edge. The model test results show that in comparison with the original runner A, the performances, such as efficiency, hump safety margin, cavitation and stability are improved in runner B.