Analysis on Nonlinear Vibrations of Mistuned Blades With Frictional Under-Platform Dampers Considering Asynchronous Excitation Force

Abstract

Abstract Turbine blades are used under increasingly severe conditions to increase the thermal efficiency of the gas turbines in operation. Friction dampers reduce vibration responses of the blades and improve the power plant reliability. One of the representative friction dampers is the under-platform damper designed to generate friction between two blade platforms and a damper pin. The under-platform damper has been widely adopted in gas turbines. It is important to predict the characteristics of vibration for turbine blades with the dampers analytically on design phase. Thus, a lot of analytical methods have been intensively proposed. However, it is very difficult to obtain analytical results showing high consistency with actual phenomena, which depend on mistuned blades with nonlinear friction dampers and on complicated excitation force included asynchronous random force. The authors indicated necessity of consideration of the two effects, i.e., synchronous harmonic excitation force and asynchronous random excitation force, in the past paper. Although some papers are specific to frictional vibration analysis on mistuned blades, there are no papers considering the effect of asynchronous excitation force. This paper presents the analytical method dealing with nonlinear vibrations of mistuned blades with under-platform dampers on actual condition considering asynchronous excitation force. The analytical results show good agreement with amplitude of vibration and variation of frequency response curves under the mistuned condition. It is suggested that analytical models should take into consideration of variation in the blade properties and asynchronous excitation force to obtain reproducible analytical results on the actual variation of each blade response.