Multiple Frequency Analysis Methods for Blade Tip-Timing Data Analysis

Blade Tip-Timing (BTT) is a method for the measurement of blade vibration in rotating bladed assemblies such as those found in turbomachinery. The system aims to replace strain gauge technology. However all current BTT analysis methods fail to recover the correct frequencies when two blade modes are excited simultaneously by a synchronous vibration. In this paper, five new methods that can recover simultaneous frequencies from BTT data are presented. The methods are based on the auto-regressive approach. The approached make use of data either from a single blade and single revolution or from multiple revolutions. Furthermore, some of the methods are designed to allow for the presence of measurement errors. The techniques are validated on three test cases in which simulated data was used. It is shown that most of the methods produce accurate estimates for the vibration frequency, even in the presence of significant noise levels, provided that a suitable amount of the response waveform is measured. The most consistent estimates are obtained from the methods that make use of data from multiple revolutions.