Session: 28-02 System Response / Blade-Tip-Timing

Paper Number: 122642

122642 - 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 the impeller. 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 a 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 at 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 have been validated through comparison with strain gauge 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.

Presenting Author: Marios Sasakaros RWTH Aachen, Institute of Power Plant Technology, Steam and Gas Turbines

Presenting Author Biography: I have completed my bachelor’s and master’s degree in mechanical engineering at RWTH Aachen University with specialization in aerospace engineering. I wrote my bachelor thesis in 2018 at the Institute of Structural Mechanics and Lightweight Design of RWTH Aachen on the numerical aeroelastic investigation of the flutter behavior of a flat plate using coupled fluid structure interaction models. My master thesis was caried out in 2020 at the Institute of Power Plant Technology, Steam and Gas Turbines of RWTH Aachen on the numerical analysis of heat transfer on a radial turbine of a turbocharger. Since February 2021 I am working as a research assistant at the Institute of Power Plant Technology, Steam and Gas Turbines of RWTH Aachen. Currently focusing on the experimental investigation of blade vibrations at the radial turbine of an exhaust gas turbocharger.

Authors:

Marios Sasakaros RWTH Aachen, Institute of Power Plant Technology, Steam and Gas Turbines
Luca Mann RWTH Aachen, Institute of Power Plant Technology, Steam and Gas Turbines
Markus Schafferus RWTH Aachen, Institute of Power Plant Technology, Steam and Gas Turbines
Manfred Wirsum RWTH Aachen, Institute of Power Plant Technology, Steam and Gas Turbines