Mathieu Mercadal

Health monitoring and prognostics of blades and disks with blade tip sensors

Blade tip sensors embedded in the engine case have been used for decades to measure blade tip clearance and blade vibration. Many sensing technologies have been used: capacitive, inductive, optical, microwave, infrared, eddy-current, pressure and acoustic. This paper outlines the technology of blade and disk health monitoring with such sensors. The basic measurement techniques are reviewed, along with damage signatures which might be recognized with such sensors. The compromise between system complexity (in terms of sensor count) and data quality is discussed.

Autonomous PHM with blade-tip-sensors: algorithms and seeded fault experience

Blade tip sensors embedded into the engine case have been used for decades to measure blade tip clearance and blade vibration. Many sensing technologies have been used; capacitive, inductive, optical, microwave, infra-red, eddy-current, pressure and acoustic. These sensors generate data streams far greater than have been historically used in engine diagnostic units. Data streams of about 10,000 samples per second per sensor are about the minimum achievable, with some sensor front-ends delivering data streams of greater than 1Megasamples per second per sensor. In a PHM application, this data cannot be stored for later human analysis, but must be analyzed and discarded. This paper outlines autonomous algorithms for the real-time analysis of this data stream for PHM purposes. The application of these algorithms to several seeded fault tests is described. The need for a series of additional seeded fault tests is highlighted, for the purpose of maturing these algorithms prior to introduction into service.

Electronic controller for an adaptively tuned vibration absorber

An apparatus for absorbing vibrations in a structural member has a mass suspended between two mounting plates by a separate springs. The mass has two sections and a mechanism for adjusting the spacing between the sections to alter the spring stiffness. Two sensors produce first and second signals representing the vibration of the structural member and the mass. The mechanism is operated by a controller that includes separate filters for the first and second signals in which each filter has a center frequency that is tuned by a clock signal. The phase comparator produces a phase output signal indicating a phase relationship between signals from the two filters and the control signal for the mechanism is produce in response to the phase output signal. A phase locked loop produces the clock signal for tuning the filters in response to a comparison between one of the first and second signals and a signal from one of the filters.

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.

Evaluation of actuation schemes used for acoustic attenuation of vibrating surfaces

This paper compares three actuation schemes to attenuate turbulent boundary layer sound radiated into the cabin through an aircraft fuselage. Two actuation schemes make use of piezoelectric materials and are compared with conventional electromagnetic voice coil actuation. Volume displacement of electromechanical actuators is typically proportional to either volts or amperes. Comparison between actuators can be problematic since drive impedances vary greatly. This paper presents a reliable method to compare actuator power using a transfer function of volume per square root of power. This power consumption curve is useful in direct comparison of actuator stroke capability and spacing requirements.