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An Acoustic Travelling Wave System for the Analysis of Blisk Mistuning

One of the few acoustic travelling wave systems (TWS) in the world has been developed by Defence Science and Technology Group Australia (DST). This system uses acoustic excitation of blisks by means of a high-powered speaker cluster. The response to this acoustic excitation is measured by a laser doppler vibrometer which shows the natural frequencies and mode shapes of the blisk. To date, this system has been verified and validated on a simple, twelve-bladed research blisk with a maximum error of 3.78% from FEM modal and harmonic analysis. Furthermore, the system has been refined and tested on a current in-service blisk with an accuracy of approximately 1%. This study outlines how the TWS has been used to investigate the effects of mistuning on blisks. Promising results have been achieved with the system able to accurately identify changes in resonant behaviour due to mistuning with correlation to finite element modelling predictions. The limitations are also outlined, along with suggested areas of research and improvement. This may ultimately result in the ability to verify manufacturer blending limits and assess the effect of foreign object damage and repairs on the dynamic response characteristics of a blisk without a complex and labour intensive mechanical spin rig investigation.