Fluid-Structure Interaction Analysis and Fatigue Life Prediction of Francis Turbine Runner using Numerical Simulation

Abstract

Hydroelectric power is currently one of the largest sources of renewable energy worldwide. Particularly in Ethiopia, more than 90% of the electrical energy is produced by hydropower in which the turbine runner is a key component of a hydroelectric turbine responsible for converting the kinetic energy of flowing water into mechanical energy that can be used to generate electricity. While doing so, the repeated stress cycles that the turbine runner undergoes during operation can cause fatigue failure and deformations and then responsible for significant financial and energy losses. Fatigue study can be conducted experimentally using real-time measurements of pressure, fluid flow, and vibration in hydraulic turbines or prototypes. As fatigue tests are time demanding, this type of fatigue study is expensive and resource demanding. Another technique is through numerical analysis which is popularly used by researchers due to complex structures of actual machines and also due to time, cost considerations. Fluid Structure Interaction (FSI) is one such numerical method which is widely used for flow induced stress study. Therefore, this research has employed FSI approach with a coupled solution of Computational Fluid Dynamics (CFD) and Finite Element study (FEA). The commercial software SOLIDWORKS 2022 and ANSYS 19.2 has been used for Modeling 3D CAD of francis turbine runner and analysing FSI respectively. Using the results of the FSI analysis, it has been found that the maximum stresses due to the water pressure are located at the trailing edge of the runner blade towards the transition between the blade and the crown. This explains why this region has been identified as a critical area for fatigue crack initiation in the Francis turbine runner. The results also show good agreement with the previous studies in the literature. It was further observed that the Francis turbine runner considered for this study has infinite life and minimum damage combined with maximum factor of safety