Measurement of out.of.plane vibrations of a rotating bladed disk using Blade Tip Timing measurement method

摘要

The aim of this paper is to compare the results of vibration measurements performed under rotating conditions using two different methods Blade Tip Timing (BTT) and Scanning LDV (SLDV). We have presented a brief overview of the rotating test rig and the redesigns were made during the past to upgrade its capabilities. In order to use the BTT system with the existing rig a new chamber was needed to install BTT probes. A series of measurements about the rotational speed fluctuations were carried out because the sensitivity of the system to those oscillations. We have presented a 24.bladed disc which was modified applying triangular wedges at the blade tips and so out.of.plane vibrations could be measured by the BTT system. The capability of such a system to measure vibrations has been demonstrated but the same was suffering in measuring very low amplitude resonance which was blurred by the background noise. However, increasing the force level, applied to the rotating blisk, the BTT system managed to measure vibrations. The comparison of the BTT results against the SLDV ones showed that BTT system was overestimating the amplitude level of the vibrations and in fact the resonances amplitude peaks were somewhat higher than the ones measured using the SLDV system. Another remark would be addressed to the slight shift in frequency of the resonances between the two systems. An explanation of the disagreement between the measured data was addressed to the imprecise positioning and manufacturing of the wedges.