Effects of Head and Discharge on Internal Flow Characteristics of a High-Quality Installed 1 GW Francis Turbine

In order to explore the flow characteristics of high-quality installed 1 GW Francis turbines, a full geometric model of the fluid domains, including spiral case, stay vane, guide vane, runner, labyrinth seals, balance tubes, and a draft tube, is established. Based on the Shear Stress Transport (SST) Turbulence model, Computational Fluid Dynamics (CFD) software is utilized to conduct numerical simulations of a 1 GW Francis turbine under rated operating condition, maximum head operating condition, and minimum head operating condition. According to simulation results, the flow state is the most stable under the rated operating condition. In addition, the pressure span in the guide vane, labyrinth seals, draft tube and other channels is uniform, and there is no flow shedding and blade passage vortex in the runner. Furthermore, the flow regime is relatively unstable in the other two operating conditions. The fluid flow impacts the blades, resulting in flow separation. There are many vortices in the draft tube, which may threaten the safe and stable operation of the turbine. Moreover, the pressure distribution trend in the fluid channel under the three operating conditions is almost the same. The results of this paper can provide a useful reference for the design and installation of giant Francis turbine units.