Non-contact blade vibration measurement analysis using a multi-degree-of-freedom model

The non-contact blade vibration measurement technique (tip timing) has been developed in the 1970s with focus on large steam turbine blades. Today, most of the turbo machine manufacturers are using tip timing for vibration amplitude or frequency evaluation of rotating blades. Different analysing methods have been developed. The most common method is a time domain analysis of a resonance passing using one- or two-blade sensors and a 1/rev sensor on the shaft. Normally, this analysing method is based on a single-degree-of-freedom resonator model. For mistuned blade rows, a single-degree-of-freedom model is not suitable. The possible errors of the single-degree-of-freedom model were repeatedly investigated. In this article, a multi-degree-of-freedom evaluation method is presented in detail. For the first time, a successful application on measurement data is reported.