PRACTICAL BLADE VIBRATION ANALYSIS USING THE RESULTS OF FREE-FREE MODAL TEST

摘要

Experimental results show that natural frequencies are often significantly affected by small differences in the construction of joints in nominally identical test pieces. But it can be difficult to find joint parameters to which the numerical predictions are sensitive. Testing in free-free condition needs no fixture; this advantage has made it cost efficient and easier to install than clamped test, especially for test pieces with complex shapes such as turbine blades. In addition clamped test often produces relatively inaccurate data. The modal analysis of a single turbine blade is investigated in this paper. The blade has been tested in free-free and clamped conditions. Finite element analysis is firstly accomplished for free-free condition and the FE model has been updated using experimental data obtained from the free-free test. The accuracy of the FE model has been verified by comparing results with the experimental data of clamped test. Good correlation between results obtained from modal test and FEA in clamped condition shows that free-free test of the blade can be used to update the FE model. Subsequently, the reconciled FE model can be fixed to find natural frequencies of the blade in clamped condition.