Three-dimensional transient simulation of a prototype pump-turbine during normal turbine shutdown

Three-dimensional numerical simulations are carried out by commercial software STAR-CCM+ to investigate the hydraulic transient and flow behaviours of a prototype pump-turbine during the normal shutdown process. The global characteristics and pressure fluctuations are analysed as the pump-turbine runs through the turbine mode, into the turbine braking mode, and finally into the reversed pump mode. As the guide vanes close, flow rate and runner torque both decrease while the rotational speed drops in response to the negative torque on the runner. The proposed approach accurately predicts the transient characteristics during the shutdown process and provides insight into the inner flow behaviour of a pump-turbine. Thus, this study has the potential to facilitate both exploration and diagnostics of faults of turbo machines during transient operation.