EXPERIMENTAL RESEARCH ON STRESS FLUCTUATIONS IN RUNNER VANES OF HIGH-HEAD PUMP-TURBINES

By measuring stress fluctuations in runner vanes of a prototype 500 m class Francis-type pump-turbine and a 1/12 reduced scale model of that pump-turbine, it was revealed that the stress fluctuations consist of (1) components of higher harmonics of runner speed n, (2) components whose frequencies are constant, that is, independent of runner speed, and (3) components caused by interference from the wicket gates. The 1st components are generated by an unequal distribution of flow properties on the periphery of the runner. The 2nd components are estimated as components of acoustic resonance in flow paths very close to the runner. Comparisons of the prototype and the model are made about the over-all amplitude and amplitudes of major frequency components of the stress fluctuations.