Analysis and Solution of a Nonsynchronous Vibration Problem in the Last Row Turbine Blade of a Large Industrial Combustion Turbine

This paper presents the analysis and corrective action taken to solve a flow-induced nonsynchronous vibration failure problem encountered in the last-stage rotating blade in a large industrial combustion turbine. A description of the fatigue failures and of temporary operation restrictions that precluded further failure is given. The results from a strain gage telemetry test are presented which show that failure was due to high vibratory stress excursions from fundamental mode vibration, which resulted from broad band buffeting excitations and very low aerodynamic damping at high levels of power and mass flow. From these data, design criteria were developed for designing a retrofittable blade that removed the operating restrictions. Telemetry test results (from the same turbine), which verified the new design, are also briefly presented and discussed. This investigation shows that the design of future high-performance exhaust end combustion turbine blading must take into account nonsynchronous excitation (buffeting) and the aeroelastic interaction between blade structure and flow, in addition to the synchronous excitations traditionally allowed for in the design process.