Optimizing probes positioning in Blade Tip Timing systems

Abstract

The monitoring of the blades in bladed disk assembly is done via a continuous determination and analysis of the blade dynamics, which is mostly subjected to different type of excitation forces inducing the synchronous and asynchronous vibration of the blades. These vibrations can cause fatigue and crack of the blade, which can damage the overall turbo-machinery. Thus, avoiding such a damage motivates the determination of the blade’s vibration. Which is done traditionally by the used of strain gauge, which unfortunately monitor only the instrumented blade but not all the blade at the same time. Nowadays, such vibration measurements are done by Blade Tip Timing (BTT) system, where the arrangement of the probe is extremely important in order to extract useful information of the blade’s vibration signal. Thus, this article proposes a simple approach for the determination of the optimal probe positioning based on the minimization of the coherence of the measurement matrix derived from the mathematical model used to infer the vibration parameters, while the blade exhibits synchronous and asynchronous vibrations.