Étude detaillée de la comparaison entre essais industriels et modèle dans quelques cas bien définis

Abstract

1. Introduction. Information on cavitation affecting hydraulic machines is obtainable from the following sources : (i) The scale model ; (ii) The prototype. Observation of the latter, however, is most usually confined to effects of cavitation, such as erosion, vibration, etc... whereas mainly cavitation figures are observed on the model, while noting effects of cavitation on machine performance. The purpose of this study, therefore, is to compare the prototype with the model in order to show the usefulness of model tests in studying cavitation problems. 2. Francis turbines. Two cases have been investigated : (i) Two 20,900 HP vertical Francis turbines at the Carla power plant (500 r.p.m. under 137 m head) showed erosion al the runner blade entrance. These machines ran for 31.6 % of the overall time in an operating range in which cavitation had been observed on the model ; (ii) The 90,000 HP vertical Francis turbines at the Genissiat power plant (150 r.p.m. under 64.5 m head) were affected by erosion at the runner blade exits. These machines ran for 10 % of the total time in an operating range in which cavitation had been observed on the model. There was close agreement between prototype and model, and in the case of the Carla turbines the visible swirl underneath the model and prototype runners was almost identical for both. 3. Kaplan and bulb turbines. No erosion was observed near the runner hub and blade leading edges of the 11,500 HP La Vanelle plant Kaplan turbine (100 r.p.m. under 6.95 m head) and the 62,500 HP Châteauneuf-du-Rhone Kaplan turbine (93.7 r.p.m. under 19.3 m head), even though the respective models had shown traces of cavitation. The marginal cavitation observed on the La Vanelle model did leave any erosion on the blades. No erosion was observed on the prototypes nor cavitation on the models of the 17,600 HP Saint-Hilaire-du-Rozier Kaplan turbine (107 r.p.m. under 10 m head) and the 12,400 HP Beaumont-Monteux bulb turbine (150 r.p.m. under 11 m head).