Abstract:
A need has been established in industry and academic publications to link an
engine’s maintenance costs throughout its operational life to its design as well as
its operations and operating conditions. The established correlations between engine
operation, design and maintenance costs highlight the value of establishing a
satisfactory measure of the relative damage due to different operating conditions
(operational severity). The methodology developed in this research enables the
exploration of the causal, physics-based relationships underlying the statistical
correlations in the public domain and identifies areas for further investigation.
This thesis describes a physics-based approach to exploring the interactions,
for commercial aircraft, of engine design, operation and through life maintenance
costs. Applying the “virtual-workshop” workscoping concept to model engine
maintenance throughout the operating life captures the maintenance requirements
at each shop visit and the impact of a given shop visit on the timing and
requirements for subsequent visits. Comparisons can thus be made between the
cost implications of alternative operating regimes, flight profiles and maintenance
strategies, taking into account engine design, age, operation and severity.
The workscoping model developed operates within a physics-based methodology
developed collaboratively within the research group which encompasses
engine performance, lifing and operational severity modelling. The tool-set of coupled
models used in this research additionally includes the workscoping maintenance
cost model developed and implements a simplified 3D turbine blade geometry,
new lifing models and an additional lifing mechanism (Thermo-mechanical
fatigue (TMF)).
Case studies presented model the effects of different outside air temperatures,
reduced thrust operations (derate), flight durations and maintenance decisions.
The use of operational severity and exhaust gas temperature margin deterioration
as physics based cost drivers, while commonly accepted, limit the comparability
of the results to other engine-aircraft pairs as the definition of operational
severity, its derivation and application vary widely. The use of a single operation
severity per mission based on high pressure turbine blade life does not permit
the maintenance to vary with the prevalent lifing mechanism type (cyclic / steady
state).