A SURVEY OF BLADE TIP-TIMING MEASUREMENT TECHNIQUES FOR TURBOMACHINERY VIBRATION

This paper aims at providing a comparative survey of current analysis methods for the interpretation of vibration data measured at turbomach inery rotor blade tips using optical laser probes. The methods are cla ssified by the form of the vibration that they attempt to identify, na mely, asynchronous and synchronous with respect to rotor speed. The pe rformance of the various techniques is investigated by using both actu al assembly measurements and simulated response data. In the latter ca se, synchronous vibration data are obtained via a multidegree-of-freed om numerical simulator that includes the structural and geometric prop erties of the bladed-disk assembly the external forcing terms, and the characteristics of the optical probe. When using experimental data, t he results of the tip tinting analysis are compared to those obtained from standard strain-gauge tests and the relative merits of the two ap proaches 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. Of particular note is the introduction of a new indirect analysis method for identifying the characteristics of synchronous vibration modes using measurements from two probes. Fi nally, new avenues for future analysis methods and further development s in tip-timing systems are also discussed.