Comprehensive stay vane vibration analysis by means of numerical and experimental approaches

Abstract

Abstract Vortex-induced vibration is the most common phenomenon associated with the development of cracks in hydraulic turbine stay vanes and although the trailing edge modification is an usual and well-known solution, its empirical application may not lead to the complete elimination of the cracks. During Ilha Solteira hydropower plant history several modifications were implemented, but only the one applied to vane 24 was successful in avoiding cracks recurrence. To better understand this phenomenon, a 2D transient Computational Fluid Dynamics (CFD) simulation was developed incorporating the fluid-structure interaction effect by allowing the simulated vane to move perpendicularly to the flow. Additionally, field measurements and laboratory experimental results were used to calibrate the numerical model. A comparison of the results obtained by CFD with the ones measured in the laboratory revealed differences smaller than 1% for the peak displacement amplitude. When applied to the prototype scale, the simulation was able to capture the lock-in effect in a frequency around the one measured at site which corresponds to the first bending mode of the vanes. A geometrical modification was developed, tested numerically and implemented at site. Later strain-gauge measurements confirmed that the modified stay vanes were no longer being excited in their first mode, resulting in a 90% reduction of the oscillating stress amplitude.