Abstract: Focused on a 1000 MW huge-capacity hydraulic turbine unit, this paper conducted three-dimensional steady internal flow numerical simulation using commercial code ANSYS. The impact of uneven clearance distribution on its internal flow characteristics of the turbine under the design operating point was investigated, considering radial installation deviations of 0.1 mm, 0.3 mm, 0.5 mm, 1.5 mm, and 2.5 mm on the negative y-direction. The results revealed that within a certain range of deviation, the pressure in the corresponding region gradually rises with the decrease in clearance. However, once the deviation exceeded a certain threshold, water was unable to flow in, thus resulting in the formation of a low-pressure area. Furthermore, both the upper crown chamber and the bottom ring chamber exhibited an equal number of vortex evolving cycles with different vortex intensity, and the vortex was more intense in the upper crown chamber; The number of vortices is not an integer multiple of the blade number. Finally, we clarify that the vortex flow impact was greater on the inner wall of the bottom ring chamber than that of the upper crown chamber. This study is applicable to the design and installation of other large or medium size Francis turbines for improving their operational quality, reducing operating costs, and enhancing the overall efficiency of hydropower plants.

Key words: 1000 MW runner, Francis turbine unit, radial installation deviation, flow characteristics, CFD