The in-situ measurement of aero-engine blade flap using an optical fibre sensor

This paper describes the principle of operation and performance characteristic of an optical system for the real-time measurement of the vibration modes of aero-engine compressor and turbine blades. The system is based on a minimally invasive, fibre optically linked sensor which enables the instantaneous blade displacement and velocity to be measured during engine operation. The primary advantages of this approach is that it is noncontacting and passive (no electronics local to the sensor are required), and it enables measurements to be made on each blade. Real-time processing of the output data enables the vibration amplitude and modes of vibration to be picked out against the random background fluctuations of the blades. The system has been developed primarily for the online diagnosis of aero-engines but may be adapted for the long term, in-situ condition monitoring of various classes of turbo machinery. An important feature of the probes is that they have been designed to operate at high temperatures (~500°C)