The blade tip clearance, inter-blade spacing, and blade angle are good indicators and predictors of engine damage. Detection of early signs of engine damage, without engine disassembly, would potentially increase the inspection intervals, as well as the aircraft availability. If the blade condition deteriorates gradually, the time it would take to reach potentially dangerous damage conditions could be predicted and maintenance measures could be planned accordingly. The existing, most common alternatives to eddy current sensors are the optical and capacitive sensors. Both are reported to be prone to effects of contaminants, such as water, oil, dust, and dirt; moreover, they are not able to simultaneously detect both blade timing and clearance, as is the case with eddy current probes. On the other hand, the effectiveness of eddy current sensors containing permanent magnets is decreased with higher temperatures and low frequency vibrations. For these reasons, the pulsed eddy current technology proposed herein represents an opportune alternative to other types of sensors. This blade condition monitoring system does not need in-flight operation, but periodically, on ground activation, with the monitoring system attached to the engine when necessary. In this way, the blade vibrations and rotating speeds, as well as temperature levels could be kept to a minimum. While detection of blade tip clearance and inter-blade spacing need only one sensing element per stage, for the detection of the blade angle, there is a need for at least two pulsed eddy current sensors per stage: one focusing on the leading edge and the other on the trailing edge of the blade. On an engine, there are many sources of errors that could inflict significant challenges to blade monitoring, such as: axial shift of the rotor during engine operation, electromagnetic interferences, vibrations, etc. Transition of this technology from room temperature, table-top experiments to the engine operating environment shall include test cell and spin rig validation. Conditions of high vibrations and temperatures need to be compensated for or calibrated against. Thermally shielded probes or monitoring at low temperature sections of the engines, such as fan and compressor stages, where foreign object damage is most likely to occur, could help with this challenge. Moreover, acquisition of baseline data is essential in quantifying the signal changes and relating them with blade position changes.
Aircraft engine blade tip monitoring using pulsed eddy current technology
2012
9 Seiten, 9 Bilder, 12 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch
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