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Algorithmic Aero Engine Life Usage Monitoring Based on Reference Analysis of Design Mission

1 ABSTRACT Fracture critical areas in an aero engine are usually located in fast rotating components which are exposed to high temperatures. Therefore, a direct local measurement of damage related parameters like strains and temperatures is not feasible. Instead, only a few remotely measured quantities, e.g. engine intake conditions, rotational speeds, and, possibly, gas path temperatures and pressures, are accessible as input for an on-board life usage monitoring system. This shortcoming has been compensated by sophisticated mathematical models which calculate the local physical parameters needed for assessing the life consumption of each critical area. The models for temperature and stress calculation consist of algorithms containing parameters which have to be adjusted individually for each considered engine area. This is achieved by an optimization with respect to a reference analysis performed for the purpose of structural life prediction which is part of the engine development process. The reference analysis is usually a finite element calculation applied to a representative flight profile (the design mission). The parameters of the algorithm are determined in such a way that the maximum deviation between the results of the algorithm and those of the reference analysis is minimized over the whole design mission. The algorithms are suitable for use in real time. They allow for fast transition of the input signals, measured under real aircraft and engine manoeuvring , to the calculated temperatures and stresses. From the temperature and stress histories of a flight, the cyclic damage is determined by application of the crack initiation or crack propagation data. Life consumption results are available immediately after the end of a flight. They are measured in units of consumed reference cycles which are defined by the most damaging cycle of the design mission. The remaining operational life of each critical area is obtained by a comparison with the respective number of reference cycles of the released service life.