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

Algorithmic Aero Engine Life Usage Monitoring
Based on Reference Analysis of Design Mission
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MANFRED KOEHL
1 ABSTRACT
Fracture critical areas in an aero engine are usually located in fast rotating com
ponents which are exposed to high temperatures. Therefore, a direct local meas
urement 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 physi
cal parameters needed for assessing the life consumption of each critical area.
The models for temperature and stress calculation consist of algorithms con
taining parameters which have to be adjusted individually for each considered en
gine 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 ma
noeuvring, to the calculated temperatures and stresses.
From the temperature and stress histories of a flight, the cyclic damage is de
termined by application of the crack initiation or crack propagation data. Life con-.