Failure analysis of runner blades in a Francis hydraulic turbine — Case study

• Failure analysis of the runner blades
• The stress analysis of the runner blades subjected to different loading conditions
• Pressure distribution by Computational Fluid Dynamics (CFD)
• Fatigue analysis simplified
• Probable causes of failure of the runner blades

Failure analysis of the moving blades in the runner of a 200 MW Francis type hydraulic turbine is presented. Analysis consisted of the determination of the pressure on the blade surface using computational fluid dynamics (CFD), the calculation of the stress distribution in the turbine runner at different operating conditions using the finite element method, and a simplified fatigue analysis. Natural vibration modes in water and Von Kármán's vortex frequencies serve as reference. Results showed a large concentration of stresses in the T-joint between the blade and crown where the cracks originated. Finally, possible causes of the damage are discussed.