THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS VIBRATIONAL RESPONSE ANALYSIS OF MISTUNED BLADED DISK SYSTEM OF GROUPED BLADES

Abstract

ABSTRACT For the purpose of the efficient analysis of a mistuned Waded disk system, a new analysis method which applies the substructure synthesis method and the modal analysis method is proposed. Using the proposed method, the vibrational characteristics of the grouped blades structure are studied. From the results, it is found that the grouped blades structure is very sensitive to the mistuning. It is also found that the mixed grouped blades structure (a bladed disk system consisting of some different types of grouped blades relating to the number of blades contained) has an undesirable effect on the forced response. Moreover, by comparing the vibrational characteristics of the integral shroud blades (ISB) structure with those of the grouped blades structure, it is clarified that the reliability of the ISB structure is superior to other sauctures also from the viewpoint of the mistuning. INTRODUCTION Some Waded disks of steam turbines consist of grouped blades in which several blades are connected into one group by elements such as a shroud or stub. When carrying out a vibration response analysis for such a bladed disk of grouped blades, the effect of the disk is usually neglected under the assumption that the stiffness of the disk is sufficiently larger than that of the blade, in order to avoid the complicated calculation. And even if taking the disk into account, all blades on a disk are assumed to be identical (tuned system). In a real bladed disk, however, the vibration of grouped blades is coupled with each other through the disk and furthermore, the vibrational characteristics of blades on a disk vary slightly due to manufacturing and material tolerances (mistuned system). Therefore, in the forced response of a mistuned system by a harmonic excitation, Eq.(1), which is a conditional equation of resonance for a tuned system (e.g.. Wagner and Griffm 1996), is no longer effective because of the split of natural frequencies or the distortion of vibrational modes, and a difference in the amplitudes among individual blades appears, causing certain blades to respond remarkably. Moreover, blades become responsive over a wider excitation frequency range than the tuned system