Session: 28-04: Experimental techniques and applications

Paper Number: 151780

A Unified Approach for the Quantitative Comparison of Strain Gauge and Blade Tip-Timing Measurement Results for Blade Vibration in Turbomachinery 

Accurate measurement of blade vibrations in turbomachinery is crucial for precise service life assessment. The most commonly employed techniques are Strain Gauge (SG) and Blade Tip-Timing (BTT) methods. While BTT has gained prominence over the past decades due to its non-intrusive nature, it is limited by undersampled data, leading to uncertainties when applied to impellers with unknown vibration frequencies. To compensate for this limitation, BTT is frequently accompanied by SG for vibration frequency identification. However, a quantitative comparison between these methods is particularly challenging due to differences in the measured quantities, sampling resolution, and evaluation procedures.   

This paper addresses the discrepancies between SG and BTT measurements and proposes a unified methodology for their quantitative correlation. Initially, a modal analysis is conducted to derive mode-dependent conversion factors between the SG measurements and the tangential deflections captured by BTT. To ensure accurate time-domain comparisons between the measurement techniques, the methodology incorporates the synchronization of their evaluation windows and validates them by comparing vibration properties such as amplitude, resonance frequency, and damping. Additionally, the actual SG position on the blade as well as the axial plane of the BTT sensors are meticulously analyzed to refine the conversion factors. 

The proposed methodology is validated using experimental data from a radial impeller acquired from an exhaust turbocharger test bench. These results not only improve the reliability and precision of vibration analysis in turbomachinery but also offer a comprehensive framework for future applications in blade health monitoring.  

Presenting Author: Markus Schafferus Institute of Power Plant Technology, Steam and Gas Turbines

Presenting Author Biography: Bachelor’s and Master’s degree in mechanical engineering specialized in aerospace technology from RWTH Aachen. Internship at GKN Aerospace in Trollhättan, working on the heat transfer at the turbine exhaust case. Bachelor and Master’s thesis written at the Institute of Jet Propulsion and Turbomachinery from RWTH Aachen on the subject of acoustic rotor-stator interactions in an axial compressor, as well as the experimental investigation of adjustable guide vanes with penny cavities in a ring-grid wind tunnel. Since June 2020 research assistant at the Institute of Power Plant Technology, Steam and Gas Turbines. Now working on the experimental investigation of blade vibrations at the radial turbine of an exhaust gas turbocharger.

Authors:

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