Development of excitation test method for non-synchronous vibration of rotating turbine blade (Measurement of damping of non-synchronous vibration mode)

Abstract

In order to analyze the blade vibration caused by flutter, it is necessary to understand both the aerodynamic damping and structural damping of the high vibration stress. Flutter Vibration mode occurring in the rated speed is non-synchronous mode. To measure non-synchronous mode damping, high frequency excitation magnet was developed. Damping characteristics of the non-synchronous mode of nodal diameter 12 and 4 were measured in the rotation test. For comparison, synchronous mode of nodal diameter 4 was measured. From these results, it was concluded as follows. (1) It is possible to excite non-synchronous mode by high frequency excitation magnet and measure the damping ratio. (2) According to the measurement results of non-synchronous mode of nodal diameter 12 and 4, damping ratio is increased if the excitation force become large. Synchronous mode of nodal diameter 4 is also a similar trend. (3) Nodal diameter 4 damping ratio of non-synchronous mode(Resonance speed : 100%) was lower than synchronous mode(Resonance speed : 75%). (4) When evaluating flutter which occurs at rated speed, it is necessary to measure structural damping ratio at rated speed.

Keywords

• turbine
• blade
• natural frequency
• non-synchronous mode
• damping
• high frequency excitation