SLDV technology for measurement of mistuned bladed disc vibration


Bladed discs are very sensitive structures and the amplitude vibration of each blade can vary significantly from blade to blade due to a series of factors such as geometrical inhomogeneity between blades or material properties. These factors lead to bladed disks mistuned thus the forced response amplitudes can be much higher than the level predicted for a tuned assembly. Designed models need to be “validate” to predict the response of a real bladed disc within the tolerances set by the manufactures and this process is very expensive as well as difficult. The validation process needs “reference data” as fundamental input against what all predictions can be compared and validated. Data that can be provided both under stationary conditions and under rotating conditions and the latter is the most difficult to achieve, especially for bladed disc assemblies which are very sensitive to any structural modification as it could be attaching a transducer to measure vibrations. There are contact-less measurement techniques available which, however, provide limited information because they can measure only limited areas of the vibrating structures. The aim of this study is to design measurement methods, using a standard Scanning Laser Doppler Vibrometer (SLDV) and to integrate it into a software platform which will be able to handle a series of measurement tasks both under stationary and rotating conditions. The main contribution of this thesis is to extend the use of Continuous Scanning LDV (CSLDV) to the rotating structures, such as bladed discs, thus to perform synchronous measurements. Hence, a bladed disc is needed to be designed to perform vibration predictions and measurements and a mathematical model of the measurement test to control, critically, all possible sources of errors involved in measurement under rotating conditions; all these to produce a robust measurement method. While the primary focus is the measurement method, the study also extends to evaluation of the sensitivity properties of the bladed disk test pieces that are the object of the measurement tool

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