Vibration localization of a multi-packet blade system

Abstract

Turbine blades are often grouped by a shroud to improve the vibration characteristics of a multi blade system. A group of blades connected by a shroud is often called a packet and a multi-packet blade system is comprised several packets. In case of a multi-packet blade system, small random property mistuning always exist among the blades due to various reasons, including operation wear, manufacturing tolerances, and material irregularities. It may causes significant changes in the vibration characteristics of a multi-packet blade system, a phenomenon called as vibration localization. Vibration localization often leads to shortening of lifetimes or unexpected failure of the multi-packet blade system. Therefore, the effect of mistuning on the localization of a multi-packet blade system should be investigated thoroughly for safe design. However, it is very difficult to identify the mistuning strength using material/geometrical parameters, since there are always several kinds of mistuning in real systems which cannot be controlled. Therefore, the variance of blade natural frequencies of a mistuned multi-packet blade system is employed to identify the mistuning strength in the present study. The purpose of the present study is to identify an effective random mistuning parameter which determines the mode localization characteristics of a multi-packet blade system.