Fatigue cracks analysis and improvement scheme of the Francis turbine runner blades

Fatigue and cracks often occur to large hydraulic turbines,which seriously affect the safety and stability of the operation of hydraulic power station.Computational fluid dynamics (CFD) simulations of the Francis turbine including the spiral case,stay vane,guide vane,runner vane and draft tube were used to analyze the stress characteristics based on the sequential fluid-structure interaction (FSI) method.The fatigue and cracks in the Francis turbine runner blades were analyzed.A triangular block for stress releasing was added at the junction of the trailing edge and crown of the runner blade to reduce the stress concentration and improve stress distribution.The analysis results show that the triangular block is effective in reducing the stress concentration and improve stress distribution of the Francis turbine runner blades.