Design Procedure of a Compact Aerodynamic Crossover Diffuser for Micro Gas Turbine Application

104 Pages·2016·11.29 MB·English

Design Procedure of a Compact
Aerodynamic Crossover Diffuser for Micro Gas
Turbine Application
by
Christiaan Johannes Burger
Thesis presented in partial fulfilment of the requirements for
the degree of Master of Engineering (Mechanical) in the
Faculty of Engineering at Stellenbosch University
Supervisors:
Prof. S.J. van der Spuy
Prof. T.W. von Backström
March 2016
Stellenbosch University https://scholar.sun.ac.za
Declaration
By submitting this thesis electronically, I declare that the entirety of the work
contained therein is my own, original work, that I am the sole author thereof
(save to the extent explicitly otherwise stated), that reproduction and pub-
lication thereof by Stellenbosch University will not infringe any third party
rights and that I have not previously in its entirety or in part submitted it for
obtaining any qualification.
Date: ...............................
Copyright © 2016 Stellenbosch University
All rights reserved.
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Abstract
Design Procedure of a Compact Aerodynamic Crossover
Diffuser for Micro Gas Turbine Application
C.J. Burger
Department of Mechanical and Mechatronics Engineering,
University of Stellenbosch,
Private Bag X1, Matieland 7602, South Africa.
Thesis: M.Eng (Mech)
March 2016
The design of a compact crossover diffuser to replace the size-limited radial
diffuser and axial de-swirl cascade of the BMT120KS MGT is discussed. A
crossover diffuser strives to combine the performance of a channel diffuser
with the operating range and efficiency of a vaneless diffuser. Continuous
aerodynamic vanes are designed to match the centrifugal impeller discharge
flow and gradually diffuse the air towards the axial combustor inlet where the
effectofswirlingflowoncombustorperformanceisexperimentallyinvestigated.
Swirling combustor flow promotes combustion intensity, reduces combustion
length, and enhances combustion stability.
The study includes the development of a one-dimensional Mean-Line Code
(MLC) which aids the designer in preliminary design and performance evalua-
tion. A three-dimensional multiple operating point optimisation is conducted
thereafterusingNumecaFineTM/Turbo). Thefinaldesignismanufacturedus-
ing a five-axis CNC milling machine and experimentally tested by modifying
the existing BMT120KS engine.
The optimised crossover diffuser and modified impeller yielded a numer-
ical increase in the total-to-static compressor stage pressure ratio from 2:93
to 3:83, increase in the static pressure recovery coefficient from 50:92% to
68:49%, and relaxed the compressor stage discharge flow angle from 84:14(cid:14) to
34:28(cid:14) (compared to the modified BMT120KS engine). Experimental results
are recorded up to a rotational speed of 106000RPM and extrapolated to the
design speed of 120000RPM. The extrapolated results indicate a thrust in-
crease from 107:3N to 220N and increase in total-to-static compressor stage
pressure ratio from 2:62 to 3:65 at 120000RPM (compared to the original
BMT120KS engine).
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Uittreksel
Ontwerpsprosedure van ‘n Kompakte Aerodinamiese
Oorgangsdiffusor vir Mikrogasturbine Toepassing
(“Design Procedure of a Compact Aerodynamic Crossover Diffuser for Micro Gas
Turbine Application”)
C.J. Burger
Departement Meganiese en Megatroniese Ingenieurswese,
Universiteit van Stellenbosch,
Privaatsak X1, Matieland 7602, Suid Afrika.
Tesis: M.Ing (Meg)
Maart 2016
Dieontwerpvannkompakteoorgangsdiffusoromdieradialelemdiffusoren
aksiale rig-lemme van die bestaande BMT120KS mikrogasturbine te vervang
wordbespreek. ‘nKompakteoorgangsdiffusorbeoogomdiewerksverigtingvan
‘n kanaaldiffusor met die bedryfsgebied van n lemlose diffusor te kombineer.
Deurlopende aerodinamiese lemme is ontwerp om die sentrifigaalkompressor
rotor uitlaatvloei geleidelik te diffundeer tot waar dit die verbrandingsruim
binne gaan met ‘n beduidende tangensiale vloeikomponent.
Die studie sluit in die ontwikkeling van ‘n een-dimensionele kode wat die
ontwerperinstaatstelom‘nkompakteoorgangsdiffusorteontwerpenteevalu-
eer. DaarnaisoptimeringgedoeninNumecaFineTM/Turbo(BVMsagteware)
en die finale ontwerp is vervaardig met behulp van ‘n vyf-as numeries beheerde
freesmasjien.
Die geoptimeerde oorgangsdiffusor en rotor lewer ‘n numeriese toename in
die totale-tot-statiese kompressor stadium drukverhouding vanaf 2:93 na 3:83,
‘ntoenameindiestatiesedrukherwinningskoëffisiëntvanaf50:92%tot68:49%,
en verminder die uitlaat-vloeihoek vanaf 84:14(cid:14) na 34:28(cid:14) (vergeleke met die
gewysigde BMT120KS enjin). Eksperimentele resultate is verkry tot by ‘n
rotasie spoed van 106000RPM en geëkstrapoleer tot die ontwerpspoed van
120000RPM. Die resultate dui op ‘n stukrag toename vanaf 107:3N na 220N
en ‘n toename in die totale-tot-statiese kompressorstadium drukverhouding
vanaf 2:62 na 3:65 (vergeleke met die oorspronklike BMT120KS enjin).
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Acknowledgements
I would like to express my sincere gratitude to God. Father, You have contin-
ually guided me and taught me that it is not about what I do, but rather for
Whom I am doing it. That love is proven in my willingness to lose and not by
my ability to succeed. In like manner I thank You for the work of Jesus Christ
on the cross which enables me to spend eternal life with You, words cannot
express my excitement! I would also like to express my sincere gratitude to
the following persons and institutions:
• My parents, Murray and Bessie Burger, who selflessly and enduringly
supported me through the good and the difficult times. Their encour-
agement and stories have carried me through the difficult times, and
their faith in me has enabled me to finish.
• David Krige, for his patience, advice, support, and friendship. I am truly
grateful to him for placing my interests above his own, helping amid the
privilege of organising his own wedding.
• My two supervisors, Prof. S. J. van der Spuy and Prof. T. W. von
Backstrom, for their guidance, advice, positive attitude, and many con-
versations pertaining to things more than merely existing. Thank you
for building me up and reminding me to dream.
• Frans-Johan Pienaar, for the prayers, wisdom, and support you have
given. May there be many more coffees and many more victories to-
gether.
• Francois Louw, Maurisha Galant, Olaf Diener, Kenny Allen, and Fine
Wilms, for all the conversations, coffee, and even tea. You all have
contributed significantly.
• CSIR, ARMSCOR and the South African Airforce, for the funding of
this project.
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Dedications
To my brother, Murray Burger...
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Contents
Declaration i
Abstract ii
Uittreksel iii
Acknowledgements iv
Dedications v
Contents vi
List of Figures ix
List of Tables xi
Nomenclature xii
1 Introduction 1
1.1 Background and Motivation . . . . . . . . . . . . . . . . . . . . 2
1.2 Previous Work on the BMT120KS at the University of Stellen-
bosch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.1 Centrifugal Impeller Design . . . . . . . . . . . . . . . . 3
1.2.2 Vaned Radial Diffuser Design . . . . . . . . . . . . . . . 4
1.2.3 Impeller-Diffuser Interaction . . . . . . . . . . . . . . . . 5
1.3 Objectives and Project Overview . . . . . . . . . . . . . . . . . 5
2 Literature Review 7
2.1 Centrifugal Compressor Principles . . . . . . . . . . . . . . . . . 7
2.1.1 Operating Principles . . . . . . . . . . . . . . . . . . . . 7
2.1.2 Impeller . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.3 Vaneless Passage Gap . . . . . . . . . . . . . . . . . . . 9
2.1.4 Diffuser and De-Swirl Cascade . . . . . . . . . . . . . . . 10
2.2 Conventional Diffuser Design . . . . . . . . . . . . . . . . . . . . 10
2.2.1 Vaneless Diffusers . . . . . . . . . . . . . . . . . . . . . . 10
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CONTENTS vii
2.2.2 Channel Diffusers . . . . . . . . . . . . . . . . . . . . . . 11
2.3 Aerodynamic Diffuser Design . . . . . . . . . . . . . . . . . . . 12
2.3.1 Cascade Diffusers . . . . . . . . . . . . . . . . . . . . . . 12
2.3.2 Tandem Cascade Diffusers . . . . . . . . . . . . . . . . . 13
2.3.3 Low Solidity Diffusers . . . . . . . . . . . . . . . . . . . 14
2.4 Compact Diffuser Design . . . . . . . . . . . . . . . . . . . . . . 16
2.5 Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.5.1 Combustor Flow and Operating Principles . . . . . . . . 18
2.5.2 Swirl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.5.3 Combustor Liner Separation . . . . . . . . . . . . . . . . 20
2.5.4 Impinging Jets as Swirl Inducers . . . . . . . . . . . . . 21
3 Design Methodology 23
3.1 Baseline Design Weaknesses . . . . . . . . . . . . . . . . . . . . 24
3.2 Conceptual Design . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.3 Design Constraints . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.4 Important Design Parameter . . . . . . . . . . . . . . . . . . . . 26
3.5 Impeller Considerations . . . . . . . . . . . . . . . . . . . . . . 26
4 Mean-Line Code 28
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.2 Code Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.3 Code Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.4 Meridional Channel Design . . . . . . . . . . . . . . . . . . . . . 31
4.4.1 Bezier Approximation . . . . . . . . . . . . . . . . . . . 31
4.4.2 Quasi-Normal Construction . . . . . . . . . . . . . . . . 31
4.4.3 Channel Construction . . . . . . . . . . . . . . . . . . . 32
4.5 Blade Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.5.1 Blade Leading Edge Design . . . . . . . . . . . . . . . . 33
4.5.2 Blade Camberline Construction . . . . . . . . . . . . . . 34
4.5.3 Blade Thickness Distribution . . . . . . . . . . . . . . . 35
4.6 Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.7 Performance Analysis . . . . . . . . . . . . . . . . . . . . . . . . 36
4.7.1 Inlet Losses . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.7.2 Blade and Passage Losses . . . . . . . . . . . . . . . . . 38
4.7.3 Discharge Losses . . . . . . . . . . . . . . . . . . . . . . 38
4.8 Code Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.9 Design Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.10 Mean-Line Design Optimisation . . . . . . . . . . . . . . . . . . 41
4.11 Optimisation Results and Code Validation . . . . . . . . . . . . 43
4.11.1 Preliminary Design . . . . . . . . . . . . . . . . . . . . . 43
4.11.2 Updated Design . . . . . . . . . . . . . . . . . . . . . . . 44
5 Numerical Analysis 45
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CONTENTS viii
5.1 Meshing - AutoGrid5TM . . . . . . . . . . . . . . . . . . . . . . 45
5.1.1 Mesh Generation . . . . . . . . . . . . . . . . . . . . . . 46
5.1.2 Grid Independence and Validity . . . . . . . . . . . . . . 47
5.2 Simulation Setup - FineTM/Turbo . . . . . . . . . . . . . . . . . 48
5.2.1 Fluid and Flow Model . . . . . . . . . . . . . . . . . . . 48
5.2.2 Boundary Conditions . . . . . . . . . . . . . . . . . . . . 48
5.2.3 Computational Setup . . . . . . . . . . . . . . . . . . . . 49
5.2.4 Simulation Convergence . . . . . . . . . . . . . . . . . . 49
5.3 Optimisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
5.3.1 Parametric Modeller - AutoBladeTM . . . . . . . . . . . 51
5.3.2 Database Generation - FineTM/Design3D . . . . . . . . . 55
5.3.3 Performance Indicator Behaviour . . . . . . . . . . . . . 57
5.3.4 Optimisation Procedure - FineTM/Design3D . . . . . . . 58
5.4 Optimised Design . . . . . . . . . . . . . . . . . . . . . . . . . . 62
6 Manufacturing and Testing 66
6.1 Manufacturing and Assembly . . . . . . . . . . . . . . . . . . . 66
6.2 Test Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
7 Results and Validation 70
7.1 Mean-Line Code Results . . . . . . . . . . . . . . . . . . . . . . 70
7.2 CFD Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
7.2.1 Impeller Performance . . . . . . . . . . . . . . . . . . . . 71
7.2.2 Compressor Stage Performance . . . . . . . . . . . . . . 72
7.3 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . 74
8 Conclusion and Recommendations 79
8.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
8.2 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Appendices 82
A Experimental Test Bench 83
List of References 85
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List of Figures
1.1 BairdMicroTurbine120KeroStart(BMT120KS)EngineOverview
and Important Design Regions . . . . . . . . . . . . . . . . . . . . . 1
1.2 a) Original BMT120KS, b) Modified BMT120KS, and c) Compact
Crossover Diffuser . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Impeller Comparison (van der Merwe, 2012) . . . . . . . . . . . . . 4
1.4 Diffuser Comparison (Krige, 2013) . . . . . . . . . . . . . . . . . . 4
1.5 Visualisation of the de Villiers (2014) Compressor Stage . . . . . . 5
2.1 Conventional Compressor Stage of a MGT . . . . . . . . . . . . . . 8
2.2 Compressor Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3 a)TandemLSD(Ohet al.,2012), b)Single-RowLSD(Abdelwahab
et al., 2007), c) Three-Row Cascade Performance (Pampreen, 1990). 14
2.4 Compact Tandem Diffusers taken from Japikse (1996) . . . . . . . . 17
2.5 Combustion Configuration and Flow. . . . . . . . . . . . . . . . . . 18
2.6 Swirl Aerodynamics with S > 0:6 (Lefebvre and Ballal, 2010). . . 20
N
2.7 Representation of a Jet in Crossflow (Lefebvre and Ballal, 2010). . . 22
3.1 Global Design Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.2 Meridional Passage Separation in Baseline Design . . . . . . . . . . 24
3.3 Axial De-Swirl Cascade Blade Separation in Baseline Design . . . . 24
3.4 Baseline Compressor Stage Operating Range . . . . . . . . . . . . . 25
3.5 Diffuser Evolution: a) Original, b) Baseline, c) Crossover Diffuser . 25
3.6 Impeller Operating Range Shift with Diffuser Addition . . . . . . . 27
3.7 BaselineConfiguration(Imp-B),andCrossoverConfiguration(Imp-
A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.1 Compressor Stage Meridional View and Stage Numbering Convention 28
4.2 Mean-Line Code Overview . . . . . . . . . . . . . . . . . . . . . . . 29
4.3 Bezier Curves with a) 4pt Approximation and b) 6pt Approximation 31
4.4 Meridional a) Mean-Line Construction, and b) Passage Comparison 32
4.5 Meridional a) Blade Angle and b) Camberline-Angle Definitions . . 33
4.6 Blade Thickness and Camber Definitions . . . . . . . . . . . . . . . 35
4.7 Possible Geometry Creations with the Mean-Line Code . . . . . . . 39
4.8 Camberline Profiles with Various Values for (cid:12) . . . . . . . . . . . . 39
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