Vibration Analysis From Simulated Tip Timing Sensor Signal Shape Modulation

Blade Tip Timing (BTT) enables non-contact and non-intrusive measurements of the vibrational behaviour of rotating blades. The classical tip timing technology is based on arrival times when blades pass sensors mounted around the casing. Various post-processing methods have been proposed in the literature to extract the vibration behaviour of the bladed disk from arrival time data. However, the accuracy of these methods to determine vibration and modal parameters suffers from inherent under-sampling of BTT. Novel solutions are needed to extend BTT capabilities to non-linear and multi-mode vibration analysis. In this paper, an alternative approach to the signal processing of BTT sensor data is presented, focusing on the actual sensor signal shape data. The approach is based on the assumption that the vibration of blades leads to a certain modulation of the sensor output. Comparing this modulation with one from a non-vibrating condition, it is possible to extract vibration information. In this numerical study, a virtual capacitance sensor and bladed disk model is introduced to simulate the sensors with adjustable signal shape functions and to generate signal shapes from passing blades for three test cases. Data processing techniques are used to extract relevant vibration data from simulated signal shapes. It could be shown that the sensor signal shapes are modulated differently depending on the vibrational state of a passing blade. Parameters such as the blade tip dimension, sensor field characteristics, excitation, rotational speed, amplitude and frequency of vibration have a discernible effect on the sensor signal shapes.