Determination of Vibration Properties and Reliable Frequency Estimation for Synchronous Vibrations Through Improved Blade-Tip-Timing Techniques Without a Once-per-Revolution Sensor

Synchronous vibrations, which are caused by periodic excitations, can have a severe impact on the service life of impellers. Blade-Tip-Timing (BTT) is a promising technique for monitoring synchronous vibrations due to its non-intrusive nature and ability to monitor all blades at once. BTT generally employs an Once-per-Revolution (OPR) sensor that is mounted on the shaft for blade identification and deflection calculation. Nevertheless, OPR sensors can be unreliable as they may be affected by shaft vibrations and their implementation can be restricted by space constraints. Moreover, the low number of BTT sensors typically leads to under-sampled deflection signals, which consequently hinders the estimation of the vibration frequencies due to aliasing problems. For this reason, BTT is commonly accompanied by strain gauge measurements on some blades. In this paper improved BTT techniques are presented, which enable the determination of vibration properties of synchronous vibrations without the need for an OPR sensor and ensure a reliable frequency assessment. Specifically, the blades are identified by unique characteristics resulting from manufacturing tolerances while the blade deflections are calculated through a novel method, which relies on the impeller’s circumferential position. Subsequently, by employing approaches based on Non-Uniform Fast Fourier Transform the vibration frequency is accurately estimated. Finally, the vibration properties are determined using regression models. The proposed BTT techniques are validated through comparison with a commercial BTT system as well as SG measurements using experimental data acquired from a turbocharger test bench. The proposed methods eliminate the need for an OPR sensor and parallel strain gauge measurements.