In order to achieve the highest reliability in operation of large hydraulic turbo-machines, it is essential, amongst other things, to determine the magnitude not only of the static but also of the dynamic stresses under all operating conditions. The adjustable guide vanes of reversible turbine-pumps, for example, form a particularly critical component from the point of view of dynamic stresses, especially during pumping operations. This paper deals with the possibilities of predicting resonance conditions and of obtaining the magnitude of dynamic stresses in full-size machines on the basis of tests on model machines. The laws of similarity for forced and self-excited vibrations as well as vibrations in resonance are derived. It is shown that all kinds of hydraulically excited vibrations can be examined by model tests. It is permissible to carry out these measurements under reduced test head, provided that for the tested components different materials are used for the model and full-scale machine, and that the head ratio model-prototype is chosen accordingly. Suitable materials for model tests are recommended. The evaluation of the dynamic stresses for the full-size machine, based on the measured data of model tests, is shown for resonant and non-resonant conditions. Further, as an example, vibration investigations are described on the movable guide vanes of a pump-turbine, that is, using the derived laws of similarity.
Hydroelastic vibrations of the covers on water turbines with the upper ring of The guide vanes
