integrated approach for stress based lifing of aero gas turbine blades

236 Pages·2014·5.12 MB·English

CRANFIELD UNIVERSITY

ABDULLAHI OBONYEGBA ABU

INTEGRATED APPROACH FOR STRESS BASED LIFING
OF AERO GAS TURBINE BLADES

SCHOOL OF ENGINEERING
DEPARTMENT OF POWER AND PROPULSION

PhD

Academic Year: 2013 - 2014

Supervisors: Dr. Panagiotis Laskaridis
Professor Riti Singh

December, 2013

CRANFIELD UNIVERSITY

SCHOOL OF ENGIEERING
DEPARTMENT OF POWER AND PROPULSION

PhD

Academic Year 2013 - 2014

ABDULLAHI OBONYEGBA ABU

INTEGRATED APPROACH FOR STRESS BASED LIFING
OF AERO GAS TURBINE BLADES

Supervisors: Dr. Panagiotis Laskaridis
Professor Riti Singh

December, 2013

This thesis is submitted in partial fulfilment of the requirements for
the degree of Doctor of Philosophy

© Cranfield University 2013. All rights reserved. No part of this
publication may be reproduced without the written permission of the
copyright owner.

ABSTRACT
In order to analyse the turbine blade life, the damage due to the combined
thermal and mechanical loads should be adequately accounted for. This is more
challenging when detailed component geometry is limited. Therefore, a
compromise between the level of geometric detail and the complexity of the
lifing method to be implemented would be necessary. This thesis therefore
focuses on how the life assessment of aero engine turbine blades can be done,
considering the balance between available design inputs and adequate level of
fidelity. Accordingly, the thesis contributes to developing a generic turbine blade
lifing method that is based on the engine thermodynamic cycle; as well as
integrating critical design/technological factors and operational parameters that
influence the aero engine blade life. To this end, thermo-mechanical fatigue was
identified as the critical damage phenomenon driving the life of the turbine
blade.
The developed approach integrates software tools and numerical models
created using the minimum design information typically available at the early
design stages. Using finite element analysis of an idealised blade geometry, the
approach captures relevant impacts of thermal gradients and thermal stresses
that contribute to the Thermo-mechanical Fatigue damage on the gas turbine
blade. The blade life is evaluated using the Neu/Sehitoglu Thermo-mechanical
Fatigue model that considers damage accumulation due to fatigue, oxidation,
and creep. The leading edge is examined as a critical part of the blade to
estimate the damage severity for different design factors and operational
parameters. The outputs of the research can be used to better understand how
the environment and the operating conditions of the aircraft affect the blade life
consumption and therefore what is the impact on the maintenance cost and the
availability of the propulsion system. This research also finds that the
environmental (oxidation) effect drives the blade life and the blade coolant side
was the critical location. Furthermore, a parametric and sensitivity study of the
Neu/Sehitoglu model parameters suggests that in addition to four previously
reported parameters, the sensitivity of the phasing to oxidation damage would
be critical to overall blade life.
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All thanks and praises belong to Allah, the almighty creator.
ACKNOWLEDGEMENTS
I wish to sincerely thank my supervisor Dr Panagiotis Laskaridis for his
guidance, support and invaluable advice, throughout my PhD research.
Many thanks to my advisor, Professor Riti Singh, for his support and
assistance. My appreciation also goes to Prof Pilidis, and to all the
Department of Power and Propulsion staff at Cranfield University.
I am very grateful to the Chief of the Air Staff of the Nigerian Air Force for
sponsoring the course. Also, the efforts and contributions by Samir Eshati,
Esmail Najafi Saatlou, Panos Giannakikis, Godwin Abbe, Luis Conssolino and
Angelinas Stamatis are highly appreciated. To Alice and the MSc students I
worked with: Alex, Pablo, Jose, Alvaro, Jon and Mazhar, I say a big thank you
for your cooperation.
Lastly, this project would not have been successfully completed without the
prayers of my parents, and the patience, endurance and painful sacrifices of
my wife and kids. Words can therefore not express my profound gratitude to
my dear parents and family.

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Publications
A . Abu, S. Eshati, P. Laskaridis, R.Singh “Aero-engine turbine blade life
assessment using the Neu/Sehitoglu damage model” International Journal of
Fatigue, In Press, Available online 28 November 2013.
A. Abu, S. Eshati, P. Laskaridis, A. Haslam “Physics based approach to gas
turbine blade thermo- mechanical fatigue life assessment”. 21st International
Symposium on Air breathing Engines, ISABE 2013. 9 -13 September, Busan
South Korea.
S Eshati, A. Abu, P. Laskaridis, Firoz Khan “Influence of humidity on the heat
transfer and creep life of high pressure gas turbine blade” Applied Thermal
Engineering, Volume 60, Issues 1–2, 2 October 2013, Pages 335-347.
Samir Eshati, Abdullahi Abu, Panagiotis Laskaridis, Anthony Haslam,
“Investigation Into The Effects of Operating Conditions and Design Parameters
on The Creep Life of High Pressure Turbine Blades In A Stationary Gas Turbine”
Mechanics and Mechanical Engineering.Vol. 15, No. 3 (2011) 237–247,
Technical University of Lodz.
Samir Eshati, Abdullahi Abu, Panagiotis Laskaridis, Anthony Haslam,
“Investigation Into the effects of operating conditions and design parameters on
the creep life of high pressure turbine blades in a stationary gas turbine engine”
10th international symposium on compressor and turbine flow systems-theory
and application areas, SYMKOM, 2011, Lodz, 26-28 October, 2011
E. Najafi Saatlou, K.G. Kyprianidis, V. Sethi, A.O. Abu, P. Pilidis, • ‘On The
Trade-Off Between Minimum Fuel Burn And Maximum Time Between Overhaul
For An Intercooled Aero Engine’ Proc. IMechE Journal of Aerospace
Engineering, In Press
W. Mohamed, V. Sethi, P. Pilidis, A.O. Abu ,A.Nasir, O. Lotfi, , ‘Evaluation of
Electricity Cost in a Growing Market’ GT2013-95466 Proceedings of ASME
Turbo Expo 2013: Power for Land, Sea and Air, Texas, June 03-07,2013.
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TABLE OF CONTENTS
ABSTRACT .......................................................................................................... iii
ACKNOWLEDGEMENTS ..................................................................................... iv
TABLE OF CONTENTS ..................................................................................... vi
LIST OF FIGURES ............................................................................................. ix
LIST OF TABLES .............................................................................................. xii
LIST OF SYMBOLS ......................................................................................... xiii
LIST OF ABBREVIATIONS ............................................................................ xviii
1 INTRODUCTION ............................................................................................. 1
1.1 Research Background .............................................................................. 1
1.2 Scope, Aim and Objectives ....................................................................... 1
1.3 Authors Contribution ................................................................................. 3
1.4 Thesis Outline ........................................................................................... 5
2 TURBINE BLADE DAMAGE MECHANISMS, LIFING AND HEAT TRANSFER
8
2.1 Common damage mechanisms ................................................................ 8
2.1.1 Creep .................................................................................................. 9
2.1.2 Fatigue .............................................................................................. 10
2.1.3 Oxidation ........................................................................................... 14
2.2 Cumulative Damage Rules ..................................................................... 16
2.2.1 Lifing Philosophies and Methods for Gas Turbine Engines ............... 18
2.3 Turbine Blade Heat Transfer and Cooling ............................................... 22
2.3.1 Turbine Blade Cooling ....................................................................... 23
2.3.2 Convective Cooling ........................................................................... 24
2.3.3 Film Cooling ...................................................................................... 24
2.3.4 Impingement Cooling ........................................................................ 24
2.3.5 Thermal Barrier Coating (TBC) ......................................................... 25
2.4 Turbine Blade Cooling Approaches ........................................................ 28
2.5 Chapter conclusions ............................................................................... 31
3 THERMO-MECHANICAL FATIGUE .............................................................. 35
3.1 Thermo- Mechanical Fatigue Concept .................................................... 35
3.2 TMF Experiments ................................................................................. 36
3.2.1 Thermo-Mechanical Fatigue Tests .................................................... 36
3.2.2 TMF Tests for Turbine Blades ........................................................... 38
3.3 TMF Damage Interactions ...................................................................... 39
3.3.1 Creep-Fatigue Interaction ................................................................. 40
3.3.2 Fatigue-Oxidation Interaction ............................................................ 40
3.4 TMF Models and Lifing Approaches ....................................................... 42
3.4.1 TMF Models ...................................................................................... 43
3.4.2 Assessment of TMF Models .............................................................. 49
3.5 Thermo-Mechanical Fatigue in Aero Engines ......................................... 50
3.5.1 Thermo-Mechanical Fatigue in Turbine Blades ................................. 51
3.6 Chapter Conclusions............................................................................... 52
4 METHODOLOGY .......................................................................................... 54
4.1 Integrated Lifing Approach: Overview and limitation ............................... 54
4.2 Engine and Aircraft Performance Simulation .......................................... 57
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4.2.1 Engine Performance ......................................................................... 57
4.2.2 Aircraft Performance ......................................................................... 59
4.3 Turbine Sizing ......................................................................................... 60
4.4 Stress Model ........................................................................................... 61
4.5 Heat Transfer Model ............................................................................... 63
4.6 Idealised LE blade Geometry .................................................................. 66
4.7 FEA Model .............................................................................................. 68
4.7.1 ABAQUS Thermal Model .................................................................. 69
4.7.2 ABAQUS Thermo-Mechanical Model ................................................ 70
4.8 Lifing Model ............................................................................................ 70
4.8.1 Neu/Sehitoglu Model Implementation ............................................... 72
4.9 TMF Life Extraction ................................................................................. 74
4.10 Severity Study ....................................................................................... 74
4.11 Chapter Conclusions ............................................................................. 75
5 TOOLS AND MODELS: RESULT ANALYSIS ............................................... 77
5.1 Performance Simulation and Turbine Sizing ........................................... 77
5.2 Heat Transfer Analysis ............................................................................ 80
5.2.1 Heat Transfer Model Verification ....................................................... 81
5.3 Finite Element Analysis (FEA) ................................................................ 83
5.3.1 Thermal Analysis .............................................................................. 83
5.3.2 Thermo-Mechanical Analysis ............................................................ 88
5.4 Life Estimation Using N-S Model ............................................................ 94
5.5 Chapter Summary ................................................................................... 97
6 GEOMETRY AND METHOD VERIFICATION ............................................... 99
6.1 Rationale for Simplified Geometry .......................................................... 99
6.2 Idealised Blade Leading Edge Geometries ........................................... 101
6.3 Comparison of FEA Results for Idealised Geometries .......................... 102
6.3.1 Temperature and Stresses Distribution ........................................... 102
6.3.2 Analysis of TMF Life ........................................................................ 107
6.4 Blade Geometry Verification ................................................................. 110
6.5 Lifing Method Verification ...................................................................... 114
6.5.1 Thermal Analysis ............................................................................ 114
6.5.2 Thermo-Mechanical Analysis .......................................................... 115
6.6 TMF Life Comparison ........................................................................... 115
6.6.1 Result Comparison ......................................................................... 117
6.7 Chapter Conclusions............................................................................. 118
7 INFLUENCE OF TMF MODEL MATERIAL PARAMETERS ........................ 120
7.1 Motivation ............................................................................................. 120
7.2 Sensitivity of TMF Model Parameters ................................................... 120
7.3 Severity of TMF Model Parameters ...................................................... 126
7.3.1 Influence of TMF Material Parameters on Severity ......................... 126
7.4 Chapter Conclusion .............................................................................. 131
8 CASE STUDIES .......................................................................................... 132
8.1 Operational Parameters ........................................................................ 132
8.1.1 Take-Off (TO) Derate ...................................................................... 133
8.1.2 Flight Length ................................................................................... 136
8.1.3 OAT at Take-Off Conditions ............................................................ 139
8.2 Design parameters................................................................................ 142
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8.2.1 The effect of RTDF on blade life ..................................................... 142
8.2.2 The Effect of Cooling Effectiveness ................................................ 145
8.2.3 The Effect of TET ............................................................................ 147
8.3 Chapter Summary ................................................................................. 148
9 THERMAL BARRIER COATING MODELLING AND ANALYSIS ................ 151
9.1 Limitations ............................................................................................. 151
9.2 TBC FEA Modelling .............................................................................. 152
9.2.1 FEA TBC Thermal Model ................................................................ 152
9.2.2 Thermo- Mechanical Model ............................................................. 153
9.3 Impact of TBC on TMF Life ................................................................... 153
9.4 Effect of TBC Thermal Expansion, Conductivity and thickness ............ 156
9.4.1 Thermal Expansion and Conductivity .............................................. 156
9.4.2 Effect of TBC Thickness on TMF life ............................................... 159
9.5 Chapter Conclusions............................................................................. 160
10 CONCLUSIONS AND FUTURE WORK .................................................... 162
10.1 Conclusions ........................................................................................ 162
10.1.1 Summary of Findings .................................................................... 164
10.2 Future Work ........................................................................................ 170
REFERENCES ............................................................................................... 173
Appendix A ................................................................................................. 185
Appendix B ................................................................................................. 192

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