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Influences of runner blade shape on the transient behaviours of pump-turbines in load rejection

The transient behaviour of the pump-turbine in load rejection is very complex, and slight changes in runner blade shape may have great influence on it. To understand the underlying flow mechanisms, the load rejection processes of two model pump-turbines with the same specific-speed but different in the runner blade inlet shape were investigated by a three-dimensional numerical simulation method. The results show that the lean angle of the runner blade leading edge impacts the evolution of backflows at the runner inlet. The backflows first emerge at the shroud side for the runner with a negative lean angle, and the backflows first emerge at the hub side for the runner with no lean angle. However, the backflows at the shroud side make more imbalanced flows in the runner passages and higher increase of pressure fluctuations in the vaneless space. As a consequence, greater radial force fluctuations on the runner blades are formed.