A Review of Analysis Techniques for Blade Tip-Timing Measurements

This paper aims at evaluating the performance of the analysis methods currently used for the interpretation of vibration data measured at turbomachinery rotor blade tips using optical laser probes. The methods are classified by the form of the vibration which they can identify, namely asynchronous and synchronous with respect to rotor speed. Both actual assembly measurements and simulated response data are used during the investigation. In the latter case, synchronous vibration data are obtained via a multi-degree-of-freedom numerical simulator, which includes the structural and geometric properties of the bladed-disk assembly, the external forcing terms and the characteristics of the optical probe. The results of the tip timing analysis are compared to those obtained from standard strain-gauge tests and the relative merits of the two approaches are discussed with emphasis on the effects of blade mistuning. Existing industry-standard tip-timing analysis techniques are found to exhibit a number of inherent limitations and suggestions were made to address these deficiencies. A detailed tip-timing case study for a steam turbine rotor is presented in some detail and other potential application areas are explored. Finally, future analysis methods and possible future developments in tip-timing systems are discussed.