Experimental investigation on the detection of fatigue failures in hydraulic turbines

Hydroelectric power stations are nowadays one of the most important ways to obtain a clean and sustainable electricity supply. Actually, hydroelectric energy is the most renewable energy used in the world. Even so, there still exists a very important potential of development in many areas in these kinds of stations. These plants use mainly 3 types of turbines, called Francis, Kaplan, and Pelton, to obtain electricity due to the flow of water through its blades. We will focus our project on the Kaplan turbines. For doing so, the core of this project was the use of a flat disk of six blades linked with a shaft, which is a simplification of a Kaplan turbine. After installing it in a test rig of reduced scale in a laboratory, some experimental analysis were carried out. The project intention was to investigate the feasibility of detecting fatigue cracks in submerged structures such as Kaplan turbine blades by means of adequate sensors, measurement techniques and signal processing tools. For that, a series of experiments have been carried out in a laboratory with a simplified structure where a fatigue failure has been artificially provoked, which keeps similarity with the cracks observed in actual hydraulic turbines. Various detection techniques have been tested and evaluated to determine their capability to achieve the expected objective. To define a representative crack, before the experiments in the laboratory, some numerical simulations have been carried out to better understand the fracture mechanisms involved, and those simulations have been used to select the best experimental set up in the laboratory machines. Software like SolidWorks or Ansys have been used to simulate the appearance and spread of a crack in the disk until the failure of the structure. To analyze the effect of fatigue in the simplified structure used, a modal analysis has been carried out using instrumentation like accelerometers, software like Labview and theory about vibrations in machines. During this project, thus, the concepts of vibrational behavior and fatigue phenomena have gone hand in hand. Results obtained were really similar between the experiments and the numerical simulations. For the most destructive frequencies, the way that our structure vibrated with a crack practically matched between the numerical simulation and the experiments. Regarding some other frequencies of higher value, results were even closer. Moreover, the variation of frequency as the crack spreads presents a characteristic shape, similar to other machines. Due to the results obtained, I can confirm that it is possible to detect fatigue cracks that appear in the blades of a turbine and identify, by the vibration of the structure, the length of that crack. Linking the brands of studies mentioned (both numerical and experimental), the results obtained, the path we have followed to obtain these results, and with further studies, the future work will try to develop predictive maintenance techniques in actual hydraulic machines in order to avoid failures in the hydroelectric power stations due to the effect of fatigueObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No ContaminantObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructur