A Theoretical Consideration on the Vibration of Turbine Blade System

抄録

Hitherto, the turbine blade of about ten centimeter long has been failed sometimes due to the fatigue caused by vibration. The cause of the failure is considered by the author to be the resonant vibration of the blade system excited by pulsating steam flow passing through the nozzle group. Turbine blades strengthened by the shroud at their periphery constitute a vibration system having normal vibrations of fixed free type and also a vibration system of fixed supported type. The latter type of vibration system has (n-1) kinds of normal mode with nearly same natural frequency. These natural frequencies coincide with each other when the stiffness of shroud is negligibly small. The first order of these vibration is apt to resonate with exciting force caused by the steam flow, when the ratio of interval of nozzles to that of blades are about two. Therefore, it is more important to avoid the resonance of fixed supported type normal vibration of the system with pulsating steam force than to avoid that of fixed free type.