Abstract
Abstract This paper describes the measurement method and results of dynamic stress for a prototype high head Francis turbine runner, blades of which had fatigue cracks near the root of the blade outlet band side within one-year operation. In order to specify the cause of the cracks, first of all, dynamic stress of the runner blade was measured throughout complete one cycle operation including start-up, no load operation, increase/decrease of load and stopping. Excessive variable strain at the portion near the crack occurred at very low rotational speed during start-up. The large strains occurring during start-up are not due to Rotor-Stator Interaction, other definite cyclic forced vibration or resonance, but the stochastic vibration. Consequently, start-up mode survey was conducted with dynamic stress measurement. As a conclusion, maintaining a small guide vane opening below a certain rotational speed is an effective indicator to reduce the strain during start-up and to minimize the damage caused by this phenomenon.
Published Version
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