In the Francis turbine, the leakage flow through the runner gaps
which are between the runner and the stator structure influences the internal
flow and hydraulic performance. Thus, the investigation for the flow characteristics
induced by the runner gaps is important. However, the runner gaps are often
disregarded by considering the time and cost of the numerical analysis.
Therefore, in this study, the flow characteristics according to runner gaps of the
Francis turbine model were investigated including the leakage flow of the runner
cone. The three-dimensional unsteady Reynolds-averaged Navier-Stokes analyses
were conducted using a scale-adaptive simulation shear stress transport as
a turbulence model for observing the influence of the leakage flow on the internal
flow and hydraulic performance. The efficiencies were decreased slightly
with runner gaps; and the complicated flows were captured in the gaps.
