An Improved Key-Phase-Free Blade Tip-Timing Technique for Nonstationary Test Conditions and Its Application on Large-Scale Centrifugal Compressor Blades

Abstract

Large-scale centrifugal compressor is an essential fluid machinery in modern industry. The blades, a critical part of compressors, always work under severe and harsh conditions and are prone to fatigue failure. Thus, a suitable monitoring technique is necessary to guarantee reliable operation of blades in the long-term. One promising, noncontact, online, technique, is the blade tip-timing (BTT) which is able to recover the vibration characteristics of all the blades simultaneously. However, improvements are still necessary to ensure the accuracy and reliability of the BTT technique for vibration monitoring of large-scale centrifugal compressors. In this article, the resolution error induced by the finite, discrete sampling is studied first. Then, the experimental random errors brought by nonstationary operating conditions are analyzed in detail and the error introduced by the compensation of the geometrical imperfection of the blades is also taken into account. An improved technique is proposed to reduce such random errors by substituting the real key-phase signal with reconstruction by means of the tip-timing signal. Experiment on a centrifugal compressor test-rig with a cracked blade is conducted to verify the effectiveness of the improved technique. Finally, a dynamic model is built to support the experimental result. This work demonstrates the reliability of the improved BTT technique for blade condition monitoring and fault warning of large-scale centrifugal compressors.