Vortex-induced stress and crack initiation of Francis turbine runner considering wide-load conditions

Francis turbines are essential for regulating and managing energy in renewable energy power systems. To investigate Vortex-induced stress distribution and crack generation mechanism of the runner of Francis turbine, the fluid-structure interaction numerical simulation is proposed, which involves analyzing the flow field and solid structure in the runner region. This method is applied to reveal the vortex characteristics of flow field in the runner with different openings of the rated water head. Furthermore, the relationship between vortex and stress is established, and the mechanism behind crack generation is analyzed. Numerical simulation results show that the flow field frequency in runner mainly falls within 0–5 f0 and 24 f0. The occurrence of 24 f0 is linked to the number of movable guide vanes, while the presence of “Y” type reflux vortex results in 4 f0 and 8 f0. Additionally, actual engineering is applied to analyze the common crack locations. Crack at intersection between blade trailing edge and lower ring shows main equivalent stress frequency in 30–50 f0 range. However, main equivalent stress frequency at intersection between blade trailing edge and upper crown is seen in the 0–10 f0 range.