Session: 28-04: Experimental techniques and applications

Paper Number: 154016

Analysis of Blade Tip Timing Data From Nonuniformly-Spaced Sensors by Discrete Wavelet Transform 

Blade Tip Timing is widely used to measure and monitor the vibration of rotating blades in real operating engines. The success of this technique relies on its robustness, non-intrusiveness and on the possibility to monitor all the blades of the row, making it preferable to the application of strain gauge / telemetry system. On the other hand, the provided dynamic signal is inherently undersampled, at least in the common Nyquist sense. Besides, the sampling times are irregularly distributed due to possible variations of the rotor speed and the non-uniform spacing of the sensors along the circumference of the casing. These properties prevent the application of analysis methods based on classical spectral analysis. On the other hand, several techniques capable of extracting useful information have been proposed and applied. Some of these techniques focus on the deflection of all the blades collected by each sensor (e.g. the traveling wave representation), observing, implicitly, the blade vibration in a fixed reference frame. On the other hand, recent methods exploit the variation of the deflection of each blade as it crosses the different sensors, observing, implicitly, the disk vibration in a rotating reference frame.

This paper describes an analysis technique formulated in the rotating reference and exploiting the non-uniformity of the sensor spacing to suppress aliasing. The analysis starts with the time-frequency representation of the signal obtained through a discrete wavelet transform. Then, aliases are suppressed through an iterative procedure. Finally, standard data processing techniques are applied for signal analysis and system identification and differ whether the rotor speed is constant or not.

The experimental data obtained on an operating last-stage blade of a steam turbine equipped with both BTT and strain gauge systems are considered for discussion and validation.

Presenting Author: Roberto Guida Ansaldo Energia

Presenting Author Biography: Roberto Guida obtained his PhD at the University of Genova in Italy. He works for Ansaldo Energia in the machine validation group.

Authors:

Roberto Guida Ansaldo Energia
Michela Marrè-Brunenghi Ansaldo Energia
Luigi Carassale University of Genova