An investigation into distribution parameters of steam turbine blade and wheel vibration measurements

Abstract

This investigation was carried out to find a concise and meaningful way of describing the steam turbine blade and wheel vibration measurements which would enable predictions from "experimental" to "production" wheels to be made with known level of confidence. A large volume of vibration measurements from many years of testing was available. For the purpose of this study it was decided to concentrate the analysis on stage six of low-pressure turbine wheels. Two types of wheels, similar in every respect except root fixation, were used. The method of obtaining and interpreting static and dynamic blade and wheel vibration frequency measurements is described. Measurements from the wheels selected for study were analysed by appropriate statistical techniques to test assumptions and hypotheses derived from long-standing experience of empirical vibration tests. It was found that statistical analysis yields results in line with engineering expectations. In specific instances relating to the use of "experimental" wheels in predicting the performance of "production" wheels the statistical analysis not only confirmed existing practice, but pointed towards a more precise foundation of the procedure of estimating dynamic frequencies for production wheels. The suitability of the use of statistical techniques for analysis of problems of this kind is discussed.