Harmonic Component Analysis of Mode Shapes for Packeted Bladed Disk

Abstract

Vibration characteristics of packeted bladed disk is complicated. To study the vibration characteristics of the governing stage bladed disk of 660mw steam turbine, cyclic symmetry method is used to calculate the mode shapes. Fourier transformation of vibration distribution in the tangential and axial direction along the circumferential of the bladed disk is applied to obtain the harmonic components. It is found that the Fourier decomposition of each blade displacement contains not only unique component, but also other components. For integrally shrouded blades, the resonance of the m nodal diameter mode can be obtained only when the corresponding natural frequency satisfies the condition ωn = kn = mn, where n is the rotational speed and m is the harmonic number. For packeted bladed disk, there are additional harmonics that resonance occurs. The harmonic components are related to the nodal diameter number when the number of blades groups and the total number of blades are given. The diagrammatic method is applied to predict the wavenumbers present in modulated eigenfunctions.