Numerical study of francis turbine flow field under small opening condition

In order to study the cause of Francis turbine abnormal oscillation under small opening condition, CFD method was adopted to analyze the flow filed and its impact on turbine stability. Numerical simulation was performed on the commercial CFD code FLUENT 6.2, using RNG κ-ε model. Through an effective validation of the computation result and detailed flow analysis, the paper showed vortices existed in runner and draft tube flow field, abnormal pressure distribution on blades and vanes, and reverse flow in guide vanes under reverse pump condition. The result shows that the unstable flow under small opening condition leads to an increase of turbine instability, and is one possible reason of the abnormal oscillation.