Internal Flow Patterns And Hydraulic Performances Of Pump-turbine

Revised pump turbine is widely used in pumped storage power plants. Compared withtandem units with turbine and pump, it is lighter in weight and much cheaper. Studies onpump turbine started late in China, and the major work was on introduction, understandingand re-absorption of foreign products. Therefore, it has very good theoretical value andapplication prospects to research on the rule of internal flow in pump turbine and its designingtechnique.This paper investigated on the flow in francis pump turbine, finished the designing ofspiral case and runner blade, researched on internal flow patterns and hydraulic performancesof pump turbine with CFD technology to guide the designing work.So far, the conventional spiral case was designed to distribute the uniform through flowcircumferentially from the nose to the end of stay vanes. As a result, the flow circulation (=RVu) at the stay vane inlet was not sufficiently uniform circumferentially, and axi-asymmetricflow was supplied toward guide vanes and runner. Since the high-head pump-turbine must beoperated under the off-designed condition, the axi-asymmetric flow may amplify the unsteadyhydraulic performances such as S-shape characteristics and the negative gradient H-Q curve,etc. The paper investigated the basic theory for the spiral case flow, and presented the newdesigning method of the advanced spiral case having the exactly uniform axi-symmetric flowfor the high-head pump-turbines.When designing the runner blades of pump turbine, it is very important to investigate onthe internal flow patterns to choose proper geometric parameters and dimensional shapes forthe channel and blade. This paper determined the shape of the channel and stream surfaces byaverage-area, proposed the channel theory according to the flow of pump turbine outlet. Thetheory ensured no impact of runner blades inlet, analyzed the projection geometry of runnerblades in the meridional plane, then determined the camber lines and the thicknesses alongthem, and thickened the cambers to get the shape of the blade for pump turbine.In order to evaluate the designing work, this paper numerically simulated the internalflow of pump turbine by means of CFD technology, analyzed the speed, pressure and energydistribution through the whole flow field of pump turbine. It is concluded that the performance is acceptable and the designing method is reliable, and the simulation can beused to improve the designing to get more advanced blade.