The Last Few Minutes Prior to a Fatigue Blade Failure in an Axial Compressor: Observations of Blade Vibration and Blade Lean

Blade-tip measurement systems are in development for monitoring and prognosis of rotor health and blade health in turbomachinery. The preliminary development of these systems suffers from lack of experience with failure signatures; technical staff are improvising with a combination of test and inspired guesswork. Perhaps mistakes are being made; it may be that mature systems of the future will use logic very different from what is being implemented by the developers today. This paper makes a small contribution to the knowledge base of failure modes and failure signatures in axial compressors. The paper describes observed signatures in data taken with a turbomachinery tip-timing system in the final 12 minutes of operation of an axial compressor before one of the blades of this axial compressor was liberated by growing crack. The crack growth was driven by a resonant vibration of that blade. The data file ends when the blade is liberated. The data system employed for this test used non-intrusive sensors. Each sensor launched a laser beam into the compressor inlet from several feet range. The blades were driven at a 2/rev synchronous resonance. This paper details signatures of impending failure on both leading edge and trailing edge measurements.