Session: 28-04: Experimental techniques and applications

Paper Number: 151774

On the Determination of Nodal Diameter Spectrum and Mistuning Quantification of Synchronous Blade Vibrations Through Blade-Tip-Timing Measurements 

Synchronous vibrations can severely impact the service life of impellers. Previous studies have demonstrated that mistuning significantly influences the nodal diameter of these vibrations. Specifically, mistuned impellers exhibit forced vibration responses comprising multiple nodal diameters, leading to asymmetric vibration expression among the impeller sectors and substantial amplitude overshoots.

Blade-Tip-Timing (BTT) is a promising technique for monitoring synchronous vibrations due to its non-intrusive nature and capability to monitor all blades simultaneously. This paper presents a novel method for calculating the nodal diameter spectrum (NDS) of synchronous blade vibrations through BTT measurements. The method utilizes the vibration properties estimated via BTT to reconstruct the blade vibrations. Since the vibration properties of the blades are not determined at the same time, the vibrations are synchronized to acquire the mistuned mode shape of the impeller. Subsequently, the NDS is determined by performing Discrete Fourier Transform (DFT) analysis on the mistuned mode shape.

Simulated data are used to assess the effect of the vibration sample point on the DFT results as well as the impact of noise. Based on these results a strategy for the determination of the NDS in a revolution is derived. Next, the method is applied to experimental data acquired from a turbocharger test bench. To investigate the consistency of the proposed method, the results of multiple datasets of the same vibration are presented. In addition, the proposed method is validated by comparing the experimental results with those acquired by forced response simulations. Finally, by employing the experimentally determined impeller mode shape and NDS mistuning quantification factors are calculated.

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
Jonte Becker RWTH Aachen, Institute of Power Plant Technology, Steam and Gas Turbines
Manfred Wirsum RWTH Aachen, Institute of Power Plant Technology, Steam and Gas Turbines
Bernd Beirow BTU Cottbus, Chair of Structural Mechanics and Vehicle Vibrational Technology