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Flow stability is extremely important for hydraulic turbines, especially for 1 GW hydraulic turbines, and has a strong impact on mesh stability. However, turbines often operate under non-design conditions, and current research on this aspect is still lacking. So a model of the fluid domains of a high-quality installed 1 GW Francis turbine was established to investigate the flow characteristics of the turbine and fluid domains. CFD simulations of a 1 GW Francis turbine under rated load and overload operation conditions were performed. According to simulation results, when the turbine is under the overload operation condition, the internal flow stability of the 1 GW hydraulic turbine can be obviously different from that of the rated load. In the overload condition, the flow field is more turbulent and a large number of vortices are generated in the draft tube, resulting in significant changes in pressure, flow rate, and output. In order to improve calculation accuracy, a pure clearance model containing only clearances and pressure balance pipes was established. The results of the full flow channel and pure clearance were compared. It was found that under the rated operating condition and the overload condition, compared with the pure clearance model, the axial force of the runner calculated by the full flow channel model is approximately 2–7% biased, the radial force is biased by approximately 7–8%, and the leakage flow is smaller. [ABSTRACT FROM AUTHOR]

The 1000 MW Francis turbine unit at the Baihetan hydropower station is the maximum capacity unit in the world at present, and it has adopted the runner type with long and short blades. For this ultra-high output Francis turbine, especially with the breakthrough runner structure, the hydraulic excitation phenomenon caused by internal dynamic and static interference is the key factor for the stability of the unit. In this study, the 1000 MW Francis turbine unit is taken as the research object, and the rated output conditions with different guide vane openings are selected for comparative analysis. The flow field structure and the pressure pulsation characteristics inside the guide vane and runner under different openings are obtained. The distribution characteristics and evolution law of the vortex in the runner under different guide vane openings are analyzed. The results show that the dynamic and static interference between the runner and the guide vane induces the local high-speed flow to appear in the vaneless area, and the larger the guide vane opening, the smaller the dynamic and static interference between the runner and the guide vane; the vortex in the runner mainly develops and evolves from the inlet to the outlet and is mainly distributed near the blade wall surface. The pressure pulsation inside the runner is mainly due to the action of dynamic and static interference. The pressure pulsation induced by the dynamic and static interferences shows a decreasing law from the runner inlet to the runner outlet. [ABSTRACT FROM AUTHOR]