Dynamic stresses in a francis turbine runner based on fluid-structure interaction analysis

Fatigue and cracks have occurred in many large hydraulic turbines after they were put into production. The cracks are thought to be due to dynamic stresses in the runner caused by hydraulic forces. Computational fluid dynamics (CFD) simulations that included the spiral case, stay vane, guide vane, runner vane, and draft tube were run at various operating points to analyze the pressure distribution on the runner surface and the stress characteristics in the runner due to the fluid-structure interactions (FSI). The dynamic stresses in the Francis turbine runner at the most dangerous operating point were then analyzed. The results show that the dynamic stresses caused by the hydraulic forces during off-design operating points are one of the main reasons for the fatigue and cracks in the runner blade. The results can be used to optimize the runner and to analyze other critical components in the hydraulic turbine.