As the key component of the steam turbine, the steam turbine blade needs to work in a complex and rigorous operating environment, which easily leads to blade cracks or even fractures and other faults. Excessive vibration is one of the main causes of blade failure, which may affect the safe and stable operation of the equipment. Therefore, it is significant to detect and analyze blade vibration characteristics. Blade tip-timing (BTT) technology has the advantages of non-contact and simple installation, which is widely used in online blade vibration monitoring of turbomachinery. In this paper, the research of using BTT technology to measure the vibration characteristic parameters of the last stage moving blade of a steam turbine with integral shroud and snubber is carried out. Firstly, a finite element model of the last stage blade is built, the stress distribution and mode shape of the blade are obtained through simulation analysis. Secondly, the blade vibration measuring experiment is accomplished on a dynamic balancing test-bed, and the synchronous vibration parameters such as resonance speed are calculated correctly under lowing speed working condition based on BTT technology. Furthermore, the strain gauge method is used simultaneously to verify the accuracy of the measurement results. The resonance frequency and engine order of the blade are measured successfully. The analysis results show that parameters such as resonance speed identified by BTT method are consistent with that measured by strain gauge method. The research results prove the effectiveness of BTT technology in measuring the vibration parameters of the last stage blade with integral shroud and snubber, which can provide reference for design rationality verification and vibration characteristics detection of the steam turbine blade.

Blade tip-timing; Finite element method; Steam turbine blade; Vibration characteristic; Strain gauge