gas path analysis for enhanced aero-engine condition monitoring and maintenance

175 Pages·2017·3.4 MB·English

Delft University of Technology

Gas path analysis for enhanced aero-engine condition monitoring and maintenance
Verbist, Michel
DOI
10.4233/uuid:e1079009-84c2-482d-afe4-e1f9fde0d137
Publication date
2017
Document Version
Final published version
Citation (APA)
Verbist, M. (2017). Gas path analysis for enhanced aero-engine condition monitoring and maintenance.
https://doi.org/10.4233/uuid:e1079009-84c2-482d-afe4-e1f9fde0d137
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GAS PATH ANALYSIS
FOR ENHANCED AERO-ENGINE CONDITION MONITORING
AND MAINTENANCE
Proefschrift
ter verkrijging van de graad van doctor
aan de Technische Universiteit Delft,
op gezag van de Rector Magnificus prof. ir. K. Ch. A. M. Luyben;
voorzitter van het College voor Promoties,
in het openbaar te verdedigen op
woensdag 1 maart 2017 om 12:30 uur
door
Michel Louis VERBIST
Ingenieur luchtvaart- en ruimtevaart,
Technische Universiteit Delft, Nederland
geboren te Willemstad, Curaçao
This dissertation has been approved by the
promotor: Prof. ir. J. P. van Buijtenen
copromotor: Dr. ir. W. P. J. Visser
Composition of the doctoral committee:
Rector Magnificus Chairman
Prof. ir. J. P. van Buijtenen Delft University of Technology
Dr. ir. W. P. J. Visser Delft University of Technology/B&B Agema
Independent members:
Prof. dr. ir. S. Klein Delft University of Technology
Prof. dr. ir. T. Tinga University of Twente
Prof. T. Grönstedt Chalmers University of Technology, Sweden
Dr. ir. A G. Rao Delft University of Technology
Ing. R. Duivis KLM Engineering & Maintenance
Prof. Dr. Ir. B.J. Boersma Delft University of Technology, reserve member
This research is supported by by the Netherlands Agency for Aerospace
Programmes NIVR as a Basic Research Program (BRP) with project number
49212N.
Copyright (cid:13)c 2017 by Michel L. Verbist 1
All rights reserved. No part of the material protected by this copyright notice
may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying, recording or by any information storage
and retrieval system, without the prior permission of the author.
ISBN 978-94-6299-536-9
1Authoremail: [email protected]
To my parents and my dearest Jivika, Kira and Nikita.

“Life is what happens to you while you’re busy making other plans.”
John Lennon

Summary
Maintenance of aero-engines is essential for safe, reliable and cost-effective air-
craft operations. Operational aero-engines deteriorate over time. This affects
their mechanical and aero-thermodynamic performance and reduces engine
safety, reliability and efficiency. However, maintenance is a major component
of the cost per fired hour of a gas turbine. Because the engines are a relatively
expensive component of an aircraft, aero-engine maintenance is an important
subject for cost reduction.
Cost-effective maintenance of gas turbine aero-engines is achieved by com-
biningtwostrategies: maintenanceatfixedintervalsandcondition-basedmain-
tenance. Whereas maintenance at fixed intervals is specified by the engine
manufacturer, condition-based maintenance is scheduled by the engine oper-
ator, which enables them to potentially optimize this process. Regular in-
spections, engine condition monitoring and performance diagnostics methods
are used to establish the degree of deterioration for scheduling condition-based
maintenance.
An important element in the maintenance process is engine overhaul. Dur-
ing this process an aero-engine is removed from the aircraft, disassembled,
cleaned, inspected, repaired as necessary, and finally tested. Detailed knowl-
edgeofengineconditionpriortooverhaulprovidesengineoperatorsandengine
repair shops with the necessary information to plan overhaul work scopes and
to help ensure a cost-effective process.
Condition monitoring methods can be used during engine tests and during
in-flightoperation. Traditionalmethodsarecapableofestimatingthecondition
of the overall engine, but lack the ability of component-level condition estima-
tion. A much better understanding of the actual condition per component can
be obtained from detailed analysis of the complete engine gas path.
The goal of this research was to solve challenges encountered with the ap-
plication of gas path analysis in the aero-engine maintenance process. Gas
path analysis (GPA) is a performance diagnostic method that can identify en-
gine modules responsible for engine performance problems without the need
forengineremovalordisassembly. Itrelatesvariationsofmeasuredengineper-
viii Summary
formanceparametersresultingfromenginedeteriorationtotheconditionofits
gas path components. The earliest GPA methods, which used linearized rela-
tionsbetweenconditionparametersandperformanceparameters,werenotsuf-
ficiently accurate for maintenance application. Advancements in performance
modelingmethods,numericalmethodsandcomputerplatformtechnologyhave
resulted in more accurate GPA methods that can be divided into two cate-
gories: empirical GPA methods and model-based GPA methods. Empirical
GPA methods use measurements obtained from the field or experiments to
correlatecomponentconditiontoengineperformancedata,andusetheinverse
of those correlations to assess engine condition from measured performance.
Model-based GPA methods, on the other hand, use thermodynamic principles
to link measured engine performance parameters to gas path component con-
dition. Even though empirical and model-based GPA methods are different
in many aspects, all GPA methods require sufficient measured performance
data and an accurate relation between gas path component condition and per-
formance parameters to provide accurate results. In practice, limited engine
operational data, inaccurate GPA tools and the absence of an information sys-
tem means that often GPA is not used effectively or not used at all in the
maintenance process.
This work is focused on three subjects. First, improving the accuracy and
reliability of a non-linear, model-based GPA tool. Second, more effectively
using available engine performance data for GPA. Third, developing an infor-
mation system concept for GPA applications. Results were obtained by using
both simulated gas turbine performance data as well as field data measured
during engine performance tests and during in-flight operation. The Gas tur-
bine Simulation Program (GSP) was used for performance simulation. GSP is
a component-based performance simulation tool with a library of component
sub-modelsthatrepresentaero-thermodynamicgaspathcomponents,mechan-
ical components and engine control components. GSP has a generic adaptive
modeling (AM) capability that can be used for model-based GPA.
The first important element of this work has been improving the accuracy
andreliabilityofmodel-basedGPAresults. Eventhoughchangesincomponent
condition from a performance perspective cannot be directly measured, they
can be modeled. More importantly, deterioration effects can be observed by
changes in performance parameters. GPA tools calculate deviations of an en-
gine’sgaspathcomponentconditionrelativetoareferenceengine. Model-based
GPA tools use gas turbine performance models to calculate these deviations.
Two sources that affect the accuracy of model-based GPA are the accuracy of
the performance model and the reference engine used.
Gas turbine performance models use the thermodynamic laws of conserva-
tion of mass, energy and momentum to simulate the interaction among gas
pathcomponents. Tosimulatethebehaviorofindividualgaspathcomponents
Summary ix
at various operating conditions, so-called component maps are used. Because
component maps describe the behavior of actual gas path components, the
accuracyofgasturbineperformancemodelsisstronglydependentontheaccu-
racy of these component maps. However, gas turbine manufacturers consider
such detailed data proprietary and as a result the required component maps
for creating accurate performance models are not available outside the man-
ufacturers’ domain. The common alternative is to use component maps that
are available in the public domain and scaling them such that they sufficiently
representthe desiredcomponent. However, scaled component maps, which are
usually scaled relative to a single operating point, are not sufficiently accurate
for GPA. To overcome this challenge, a more detailed scaling method was in-
vestigated that used large volumes of on-wing measured performance data of
recently overhauled engines. By using large volumes of engine performance
dataavailable forawideoperatingrange, thecomponent mapscouldbetuned
with more detail. The tuned maps captured the behavior of the real gas path
componentmoreaccuratelyandtherebyimprovedtheaccuracyofGPAresults.
Additional improvements to the accuracy and reliability of GPA were ob-
tained by using multiple reference engines to calculate the condition of an
engine. Because operational engines with a good overall condition, which can
serve as a reference engine, still show significant component condition devia-
tions relative to each other, selecting the right engine is important for obtain-
ing reliable GPA results. Because every engine has its own deterioration and
maintenancehistory,selectingareferenceenginebyconsideringonlyitsoverall
conditionmaynotbesufficient. Usingmultiplereferenceenginesforestimating
the condition of a single engine takes this engine-to-engine variation into ac-
count and improves the reliability of the GPA results. Because each reference
engine provides slightly different component condition estimations, the varia-
tion of multiple reference engines provides a way to visualize the uncertainty
of the estimated component condition.
The second important element has been the development of methods to
more effectively use GPA in the aero-engine maintenance process. Tradition-
ally,engineperformanceafteroverhaulistestedduringmandatoryperformance
acceptance tests. Because those tests are expensive and time-consuming few
engines are tested before being overhauled. As a result, maintenance work
scopes are often planned without knowing the detailed condition of gas path
components. Becauseefficientgasturbineoperationistheresultofafine-tuned
balanceamongtheperformanceofitsgaspathcomponents,knowingtheircon-
dition is essential for effective maintenance. On-wing measured performance
data would provide an excellent opportunity to obtain that information. By
analyzing those data with GPA, detailed in-flight component condition data
can be obtained, which provides an excellent alternative to performance tests
prior to engine overhaul at minimal additional cost and time.