Parameter identifications of synchronous vibration of rotating blades with large amplitude based on blade tip timing

Abstract

Blade Tip Timing (BTT) is a promising method to measure the vibration of rotating blades by installing probes on the casing. The Zablotsky-Korostelev Single Parameter Technique (SPT) is widely used to identify the vibrational characteristics of blade synchronous responses. This method assumes that the influence of blade’s own vibration on arrival time can be neglected. However, it is reported that vibrations of rotating blades with large amplitudes will cause errors in identifying maximum vibration amplitude because of the above-mentioned assumption. In this paper, we derived a mathematical model of single degree of freedom (SDOF) blade model discarding the assumption of small amplitude related to BTT actual measurement. Compared to traditional SPT, our model takes the influence of blade’s own vibration into consideration. Then, we improved SPT and derived a precise measurement formula. Arrival time of blade to the sensor was revised. Based on this, we conducted a parametrical study on the effects of changes in various factors including excitation force, damping ratio, engine order, and the installation position of the sensor by numerical simulations. Displacements between considering blade’s own vibration and not were compared. Errors in fitted parameters were also analyzed. The numerical simulation results show that large engine order will magnify the error in fitted parameters if traditional SPT was used. Damping ratio and maximum vibration amplitude have relatively large errors in fitting parameters. Furthermore, we designed an experimental bench to verify the mathematical model and the revised measurement formula.