Dynamic evolution of rotating stall in a model pump-turbine during runaway transient scenario: three-dimensional simulation

Rotating stall, the phenomenon of unevenly distributing stall cells rotating in the runner, is one of the most unfavorable flow patterns in the pump-turbine. It occurs at off-design operating conditions and always induces intensive pressure pulsations and hydraulic vibrations, and may cause structural failures of the pump-turbine. Therefore, the characteristics of the rotating stall should be investigated thoroughly at all possible operating conditions. In this study, the rotating stall phenomenon in a model pump-turbine during the runaway transient scenario was simulated by the three-dimensional numerical model. The entire process of the formation of the rotating stall in this scenario was analyzed by the spatial distributions of channel discharges in the runner and their time-varying features. The results show that the rotating stall evolves dynamically and demonstrates irregular local variations. The runner channel discharges can recognize the rotating stall effectively and describe their characteristics semi-quantitatively. This study presents some understandings about the rotating stall in transient scenarios and may contribute to the reveal of the reasons for the hydraulic instabilities of pump-turbines during these scenarios.