Eventos Anais de eventos
COBEM 2017
24th ABCM International Congress of Mechanical Engineering
Vortex-induced cracks on stay vanes of a Francis turbine: An application of experimental and numerical analysis
Submission Author:
Ricardo Sampaio , SP
Co-Authors:
Alexandre D Agostini Neto, Humberto Gissoni, Vicente Borri, Renato Castilho, Ricardo Sampaio
Presenter: Ricardo Sampaio
doi://10.26678/ABCM.COBEM2017.COB17-1440
Abstract
Stay Vane cracks on a 105 MW, 73 m head Francis turbine have been reported since 1974 and this cracks issue was never completely solved. Although Voith Hydro was not the original manufacturer of the turbine, all the information was available to execute an engineering diagnostic of the reported problem and to propose a profile modification able to eliminate the cracks occurrence. This work describes the activities performed for diagnosing the Vortex Induced Vibration phenomenon occurring at stay vane profiles with associated cracks history and the resulting trailing edge modification. Firstly modal analysis by the Finite Element Method and by an analytical model based on the plate and potential flow theories were used to evaluate the natural frequencies of the stay vanes both in air and water. Results obtained from a bump test in air performed at site were used to evaluate both methods. Then stay vanes vibration was measured indirectly at the prototype. The combination of modal analysis and experimental data revealed that the second natural frequency of the stay vanes was being excited. The actual stay vane profiles were obtained by 3D measurement techniques and transient Computational Fluid Dynamics simulations were performed to numerically reproduce the phenomenon occurring in the original stay vane profile and to develop and validate a profile modification able to eliminate the vortex shedding. The geometrical modification was implemented at site and a second measurement vibration campaign happened on April 2017 revealing that the second natural frequency is no longer being excited. Although a higher frequency vibration was measured, in August 2017 there was a visual inspection of the vanes and no cracks were found.
Keywords
Stay Vanes, vortex induced vibrations, Vortex shedding, Indirect measurements
