Nonlinear Vibration by Asynchronous Excitation Force in Friction Damper of Turbine Blade

Abstract

Turbine blades are being used under increasingly severe conditions in order to increase the thermal efficiency of the gas turbines in which they run. Friction dampers are often used in order to reduce vibration along the blade and increase the plant reliability. Blades using the friction between platforms and dampers have been widely adopted in gas turbines. Characteristics of dynamical response of blades with friction dampers depend on excitation force. It is well known that there are excitation components corresponding to the number of nozzles and of combustors. Theses excitation forces are synchronous for rotation speed. Therefore, blade vibration is often calculated with single harmonic balance method. However, asynchronous components exist actually in excitation force and make it difficult to predict resonant frequency of the blades. In this study, we have developed a new method for predicting the characteristics of nonlinear vibration under excitation force including synchronous and asynchronous components. In order to investigate the effect of asynchronous components, time history response analysis and experiments using a mock-up blade were conducted. Analytical and experimental result showed dampers were slipped easily under the excitation force including synchronous and asynchronous components. Moreover, it is possible to predict the characteristics of vibration accurately by estimating the ratio of overall excitation force to single harmonic excitation force.