Handbook ofTurbomachinerySecond EditionRevised and
Expandededited byEarl Logan, Jr.Ramendra RoyArizona State
UniversityTempe, Arizona, U.S.A.MARCE L D E K K E R , INC . NE W Y
O RK B AS ELD E K K E RCopyright 2003 Marcel Dekker,
Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37
ICT 2012The rst edition was published as Handbook of
Turbomachinery, edited by EarlLogan, Jr. (Marcel Dekker, Inc.,
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Marcel Dekker, Inc.113.22.81.34 downloaded 0824709950.pdf at Sat
Apr 14 14:09:37 ICT 2012MECHANICAL ENGINEERINGA Series of Textbooks
and Reference B ooksFounding EditorL. L. FaulknerColumbus Division,
Battelle Memorial Instituteand Department of Mechanical
EngineeringThe Ohio State UmversitvColumbus, Ohio1 Spring
Designer's Handbook, Harold Carlson2 Computer-Aided Graphics and
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Applied Engineering Mechanics Statics and Dynamics, G Boothroyd
andC Poh6. Centrifugal Pump Clinic, Igor J Karassik7.
Computer-Aided Kinetics for Machine Design, Daniel L Ryan8.
Plastics Products Design Handbook, Part A Matenals and Components,
PartB Processes and Design for Processes, edited by Edward Miller9
Turbomachmery Basic Theory and Applications, Earl Logan, Jr10
Vibrations of Shells and Plates, Werner Soedel11 Flat and
Corrugated Diaphragm Design Handbook, Mario Di Giovanni12.
Practical Stress Analysis in Engineering Design, Alexander Blake13
An Introduction to the Design and Behavior of Bolted Joints, John
H.Bickford14 Optimal Engineering Design Pnnciples and Applications,
James N Siddall15 Spring Manufacturing Handbook, Harold Carlson16.
Industrial Noise Control Fundamentals and Applications, edited by
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Protection Handbook, edited by Philip ASchweitzer20 Gear Dnve
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John D. Constance22. CAD/CAM Systems Planning and Implementation,
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E.PasserelloCopyright 2003 Marcel Dekker, Inc.113.22.81.34
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Transfer Fluids and Systems for Process and Energy
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Second Edition, Daniel L Ryan39 Electronically Controlled
Proportional Valves Selection and ApplicationMichael J Tonyan,
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Gauge Division, edited by PhilipW Harland41 Fabric Filtration for
Combustion Sources Fundamentals and Basic Tech-nology, R P
Donovan42 Design of Mechanical Joints, Alexander Blake43 CAD/CAM
Dictionary, Edward J Preston, George W Crawford and Mark
ECoticchia44 Machinery Adhesives for Locking, Retaining, and
Sealing, Girard S Haviland45 Couplings and Joints Design,
Selection, and Application, Jon R Mancuso46 Shaft Alignment
Handbook, John Piotrowski47 BASIC Programs for Steam Plant
Engineers Boilers, Combustion, FluidFlow, and Heat Transfer, V
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contributionsby Thomas C. Boos, Ross S Culverhouse, and Paul F
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Ultrasonics Fundamentals, Technology, Applications Second
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Element Modeling Practical Problem Solving for Engineers,Jeffrey M
Steele67 Measurement and Instrumentation in Engineering Principles
and BasicLaboratory Experiments, Francis S Tse and Ivan E Morse68
Centnfugal Pump Clinic Second Edition, Revised and Expanded, Igor
JKarassik69 Practical Stress Analysis in Engmeenng Design Second
Edition, Revisedand Expanded Alexander Blake70 An Introduction to
the Design and Behavior of Bolted Joints SecondEdition, Revised and
Expanded, John H Bickford71 High Vacuum Technology A Practical
Guide, Marsbed H Hablanian72 Pressure Sensors Selection and
Application, Duane Tandeske73 Zinc Handbook Properties, Processing,
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Andrzej Weronski and Tadeusz Hejwowski75 Classical and Modern
Mechanisms for Engineers and Inventors, Preben WJensen76 Handbook
of Electronic Package Design, edited by Michael Pecht77 Shock-Wave
and High-Strain-Rate Phenomena in Materials, edited by MarcA
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Simplified and Graphical Techniques, Second Edition,Revised and
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Matenals, Manufactunng, and Design, SecondEdition, Revised and
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and Applications, Second Edition, Revisedand Expanded, Earl Logan,
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and Prevention, Raymond G BayerCopyright 2003 Marcel Dekker,
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ICT 201292. Mechanical Power Transmission Components, edited by
David W Southand Jon R. Mancuso93 Handbook of Turbomachmery, edited
by Earl Logan, Jr94 Engineenng Documentation Control Practices and
Procedures, Ray EMonahan95 Refractory Linings Thermomechamcal
Design and Applications, Charles A.Schacht96 Geometric Dimensioning
and Tolerancing Applications and Techniques forUse in Design,
Manufacturing, and Inspection, James D. Meadows97. An Introduction
to the Design and Behavior of Bolted Joints' Third Edition,Revised
and Expanded, John H. Bickford98. Shaft Alignment Handbook Second
Edition, Revised and Expanded, JohnPiotrowski99. Computer-Aided
Design of Polymer-Matnx Composite Structures, edited bySuong Van
Hoa100 Friction Science and Technology, Peter J. Blau101.
Introduction to Plastics and Composites. Mechanical Properties and
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Mechanics in Design, Alexander Blake103. Pump Characteristics and
Applications, Michael W Volk104 Optical Principles and Technology
for Engineers, James E. Stewart105 Optimizing the Shape of
Mechanical Elements and Structures, A A. Seiregand Jorge
Rodriguez106 Kinematics and Dynamics of Machinery, Vladimir
Stejskal and MichaelValasek107. Shaft Seals for Dynamic
Applications, Les Horve108 Reliability-Based Mechanical Design,
edited by Thomas A Cruse109 Mechanical Fastening, Joining, and
Assembly, James A Speck110 Turbomachmery Fluid Dynamics and Heat
Transfer, edited by Chunill Hah111. High-Vacuum Technology. A
Practical Guide, Second Edition, Revised andExpanded, Marsbed H.
Hablanian112. Geometric Dimensioning and Tolerancing Workbook and
Answerbook,James D. Meadows113. Handbook of Materials Selection for
Engineering Applications, edited by GT Murray114. Handbook of
Thermoplastic Piping System Design, Thomas Sixsmith andReinhard
Hanselka115. Practical Guide to Finite Elements. A Solid Mechanics
Approach, Steven MLepi116. Applied Computational Fluid Dynamics,
edited by Vijay K. Garg117. Fluid Sealing Technology, Heinz K.
Muller and Bernard S. Nau118. Fnction and Lubrication in Mechanical
Design, A. A. Seireg119. Influence Functions and Matrices, Yuri A.
Melnikov120. Mechanical Analysis of Electronic Packaging Systems,
Stephen A.McKeown121. Couplings and Joints Design, Selection, and
Application, Second Edition,Revised and Expanded, Jon R.
Mancuso122. Thermodynamics' Processes and Applications, Earl Logan,
Jr.123. Gear Noise and Vibration, J Derek Smith124. Practical Fluid
Mechanics for Engineering Applications, John J. Bloomer125 Handbook
of Hydraulic Fluid Technology, edited by George E. Totten126. Heat
Exchanger Design Handbook, T. KuppanCopyright 2003 Marcel Dekker,
Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37
ICT 2012127 Designing for Product Sound Quality Richard H Lyon128
Probability Applications in Mechanical Design, Franklin E Fisher
and Joy RFisher129 Nickel Alloys, edited by Ulrich Heubner130
Rotating Machinery Vibration Problem Analysis and
Troubleshooting,Maurice L Adams Jr131 Formulas for Dynamic
Analysis, Ronald L HustonandC Q Liu132 Handbook of Machinery
Dynamics, Lynn L Faulkner and Earl Logan, Jr133 Rapid Prototyping
Technology Selection and Application, Kenneth GCooper134
Reciprocating Machinery Dynamics Design and Analysis Abdulla
SRangwala135 Maintenance Excellence Optimizing Equipment Life-Cycle
Decisions, edi-ted by John D Campbell and Andrew K S Jardme136
Practical Guide to Industrial Boiler Systems, Ralph L Vandagnff137
Lubrication Fundamentals Second Edition, Revised and Expanded, D
MPirro and A A Wessol138 Mechanical Life Cycle Handbook Good
Environmental Design and Manu-facturing, edited by Mahendra S
Hundal139 Micromachinmg of Engineering Materials, edited by Joseph
McGeough140 Control Strategies for Dynamic Systems Design and
Implementation, JohnH Lumkes, Jr141 Practical Guide to Pressure
Vessel Manufacturing, Sunil Pullarcot142 Nondestructive Evaluation
Theory, Techniques, and Applications, edited byPeter J Shull143
Diesel Engine Engineering Thermodynamics, Dynamics, Design,
andControl, Andrei Makartchouk144 Handbook of Machine Tool
Analysis, loan D Mannescu, Constantin Ispas,and Dan Boboc145
Implementing Concurrent Engineering in Small Companies, Susan
CarlsonSkalak146 Practical Guide to the Packaging of Electronics
Thermal and MechanicalDesign and Analysis, Ah Jamnia147 Bearing
Design in Machinery Engineering Tnbology and Lubrication,Avraham
Harnoy148 Mechanical Reliability Improvement Probability and
Statistics for Experi-mental Testing, R E Little149 Industrial
Boilers and Heat Recovery Steam Generators Design, Ap-plications,
and Calculations, V Ganapathy150 The CAD Guidebook A Basic Manual
for Understanding and ImprovingComputer-Aided Design, Stephen J
Schoonmaker151 Industrial Noise Control and Acoustics, Randall F
Barren152 Mechanical Properties of Engineered Matenals, Wole
Soboyejo153 Reliability Verification, Testing, and Analysis in
Engineering Design, Gary SWasserman154 Fundamental Mechanics of
Fluids Third Edition, I G Curne155 Intermediate Heat Transfer,
Kau-Fui Vincent Wong156 HVAC Water Chillers and Cooling Towers
Fundamentals, Application, andOperation, Herbert W Stanford III157
Gear Noise and Vibration Second Edition, Revised and Expanded,
JDerek SmithCopyright 2003 Marcel Dekker, Inc.113.22.81.34
downloaded 0824709950.pdf at Sat Apr 14 14:09:37 ICT 2012158.
Handbook of Turbomachmery Second Edition, Revised and Expanded,Earl
Logan, Jr., and Ramendra RoyAdditional Volumes in
PreparationProgressing Cavity Pumps, Downhole Pumps, and Mudmotors,
Lev NelikPiping and Pipeline Engineering- Design, Construction,
Maintenance,Integnty, and Repair, George A. AntakiTurbomachmery.
Design and Theory, Rama S. Gorta and Aijaz AhmedKhanMechanical
Engineering SoftwareSpring Design with an IBM PC, Al D
ietnchMechanical Design Failure Analysis- With Failure Analysis
System Softwarefor the IBM PC, David G. UllmanCopyright 2003 Marcel
Dekker, Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14
14:09:37 ICT 2012Preface to the Second EditionThe original intent
of this bookto serve as a reference work inturbomachinery for
practicing engineers and graduate studentsremainsunchanged in this
new edition.In this edition the Introduction has been expanded to
include newmaterial on the mechanical and thermal design
considerations for gasturbine engines. Four new chapters, written
by experts in their respectivesubjects, have been added. The
chapter on steam turbines has beencompletely rewritten and
represents a major improvement to the book. Newmaterial has also
been added to the chapter on turbomachines in rocketpropulsion
systems.The original editor, Earl Logan, Jr., was joined by
Ramendra Roy inthe editing of this new edition. Both editors would
like to express theirsincere appreciation to Ms. Elizabeth Curione,
the production editor atMarcel Dekker, Inc., for her help in the
preparation of the manuscript.Earl Logan, Jr.Ramendra P.
RoyCopyright 2003 Marcel Dekker, Inc.113.22.81.34 downloaded
0824709950.pdf at Sat Apr 14 14:09:37 ICT 2012Preface to the First
EditionThis book is intended as a reference work in Turbomachinery
for practicingengineers and graduate students. The goal of the book
is to provide rapidaccess to information on topics of
turbomachinery that is otherwisescattered in reference texts and
technical journals.The contributors are experts in their respective
elds and offer theinexperienced reader the benet of their wide
experience. The practicingengineer or student can quickly
comprehend the essential principles andmethods of a given area in
Turbomachinery by carefully reading theappropriate chapter.The
material of this handbook comprises equations, graphs,
andillustrative examples of problems that clarify the theory and
demonstrate theuse of basic relations in performance calculations
and design. Line drawingsand photographs of actual equipment are
also presented to aid visualcomprehension of design features.In
each chapter the authors provide an extensive list of references
thathave been found to be particularly useful in dealing with
Turbomachineryproblems in the category considered.Earl Logan,
Jr.Copyright 2003 Marcel Dekker, Inc.113.22.81.34 downloaded
0824709950.pdf at Sat Apr 14 14:09:37 ICT 2012ContentsPreface to
the Second EditionPreface to the First EditionContributors1.
IntroductionEarl Logan, Jr., Vedanth Kadambi, and Ramendra Roy2.
Fluid Dynamics of TurbomachinesLysbeth Lieber3. Turbine Gas-Path
Heat TransferCharles MacArthur4. Selection of a Gas Turbine Cooling
SystemBoris GlezerCopyright 2003 Marcel Dekker, Inc.113.22.81.34
downloaded 0824709950.pdf at Sat Apr 14 14:09:37 ICT 20125.
Unsteady Flow and AeroelasticityL He6. Fundamentals of Compressor
DesignRobert O. Bullock7. Fundamentals of Turbine DesignDavid M.
Mathis8. Steam TurbinesThomas H. McCloskey9. Multidisciplinary
Design Optimization for TurbomachineryJohn N. Rajadas10.
Rotordynamic ConsiderationsHarold D. Nelson and Paul B. Talbert11.
Turbomachines in Rocket Propulsion SystemsDavid Mohr12.
Turbomachinery Performance TestingNathan G. Adams13. Automotive
Superchargers and TurbochargersWilliam D. Siuru, Jr.14. Tesla
TurbomachineryWarren Rice15. Hydraulic TurbinesV. Dakshina
MurtyCopyright 2003 Marcel Dekker, Inc.113.22.81.34 downloaded
0824709950.pdf at Sat Apr 14 14:09:37 ICT 2012ContributorsNathan G.
Adams The Boeing Company, Mesa, Arizona, U.S.A.Robert O. Bullock*
Turbine Engine Division, Allied Signal Company,Phoenix, Arizona,
U.S.A.Boris Glezer Consultant, Optimized Turbine Solutions, San
Diego,California, U.S.A.L He, B.Sc., M.Sc., Ph.D. School of
Engineering, University of Durham,Durham, EnglandVedanth Kadambi
Honeywell Engines and Systems, Phoenix, Arizona,U.S.A.Lysbeth
Lieber Honeywell Engines and Systems, Phoenix, Arizona, U.S.A.*
DeceasedCopyright 2003 Marcel Dekker, Inc.113.22.81.34 downloaded
0824709950.pdf at Sat Apr 14 14:09:37 ICT 2012Earl Logan, Jr.,
Ph.D.{Department of Mechanical and AerospaceEngineering, Arizona
State University, Tempe, Arizona, U.S.A.Charles MacArthur U.S. Air
Force Research Laboratory, Wright-Patterson Air Force Base, Ohio,
U.S.A.David M. Mathis Honeywell Aerospace, Tempe, Arizona,
U.S.A.Thomas H. McCloskey Aptech Engineering Services,
Sunnyvale,California, U.S.A.David Mohr D&E Propulsion, Inc.,
Mims, Florida, U.S.A.V. Dakshina Murty, P.E., Ph.D. Department of
Mechanical Engineering,University of Portland, Portland, Oregon,
U.S.A.Harold D. Nelson Department of Mechanical and Aerospace
Engineering,Arizona State University, Tempe, Arizona, U.S.A.John N.
Rajadas Department of Mechanical and Aerospace Engineering,Arizona
State University East, Mesa, Arizona, U.S.A.Warren Rice Arizona
State University, Tempe, Arizona, U.S.A.Ramendra Roy Department of
Mechanical and Aerospace Engineering,Arizona State University,
Tempe, Arizona, U.S.A.William D. Siuru, Jr.{U.S. Air Force,
Colorado Springs, Colorado,U.S.A.Paul B. Talbert Honeywell Engines,
Systems and Services, Phoenix,Arizona, U.S.A.{ Deceased{
RetiredCopyright 2003 Marcel Dekker, Inc.113.22.81.34 downloaded
0824709950.pdf at Sat Apr 14 14:09:37 ICT 20121IntroductionEarl
Logan, Jr.*, and Ramendra RoyArizona State University, Tempe,
Arizona, U.S.A.Vedanth KadambiHoneywell Engines and Systems,
Phoenix, Arizona, U.S.A.Turbomachines are devices that feature the
continuous ow of a uidthrough one or more rotating blade rows.
Energy, as work, is extracted fromor transferred to the uid by the
dynamic action of the blade rows. If energyis extracted from the
uid by expanding it to a lower pressure, the devicesare called
turbines (steam, gas, or hydraulic). If energy is transferred to
theuid, thereby increasing its pressure, the devices are termed
pumps,compressors, or fans. Stationary vanes guide the ow of uid
before and/or after the rotating blade rows.Turbomachines can be
broadly classied according to the direction ofuid ow through it. In
radial-ow turbomachines the ow is usually towardthe larger radius
for pumps, compressors, or fans and radially inward forturbines. In
axial-ow turbomachines the ow is mainly parallel to the axisof
rotation of the machine so that the nominal uid inlet and outlet
radii in* DeceasedCopyright 2003 Marcel Dekker, Inc.113.22.81.34
downloaded 0824709950.pdf at Sat Apr 14 14:09:37 ICT 2012each
turbine stage is approximately the same. The Euler
turbomachineryequation, which relates the work transfer between the
uid and the machinestage to the change in uid velocity exiting the
stage with respect to thatentering, embodies the aforementioned
characteristics. For the radial-owturbomachines, the work
transferred is determined by changes in thevelocity angle as well
as by changes in the radius. For the axial machines, thework
transferred is determined mainly by changes in the velocity angle.
Therate of energy (that is, power) transfer is the product of the
torque exertedby the rotating blades on the uid (or vice versa) and
the rotor angular speedin radians per second.A turbomachine may be
without a stationary shroud (extendedturbomachine such as aircraft
and ship propeller, and wind turbine).Alternatively, it may be
enclosed in a stationary casing (enclosed machinesuch as aircraft
engine, steam and gas turbine for power generation, andpump).The
present chapter contains an introduction to turbomachines in
twoparts, each addressing a different aspect of the subject. Part 1
provides ahistorical background of turbomachines. Part 2 introduces
the methodsused in the design of gas turbines, specically dealing
with the mechanicaland thermal design considerations. In addition
to the introductory chapterthere are 14 chapters covering various
aspects of turbomachinery in thisvolume. Chapter 2 introduces the
reader to the characteristics of the ow inturbomachinery components
and the use of computational uid dynamics inthe design of
compressors and turbines. Chapter 3 describes the progressmade,
through theory and experiment, in turbine gas-path heat
transferduring the last 50 years. Chapter 4 focuses on the
selection of coolingsystems in gas turbines.Chapter 5 discusses
unsteady ow effects in turbomachinery. Chapter6 presents design
methods that are applied to compressors, while Chapter 7develops
design methods for turbines. The theory and design of steamturbines
are elaborated in Chapter 8, and design optimization methods
forturbomachinery are discussed in Chapter 9. The dynamic behavior
ofturbomachine rotors is detailed in Chapter 10, while Chapter 11
presents thedesign of turbines and pumps used in rocket propulsion
systems. Themethods for testing of turbomachinery components are
explained inChapter 12. Automative applications are considered in
Chapter 13.In Chapter 14, models used in the analysis and design of
Teslaturbomachines are discussed. Chapter 15 treats modern
hydraulic turbines.Each chapter provides the reader with
appropriate references and usesits own notation. Coordination of
related material found in more than onechapter may be accomplished
by the readers use of the index.Copyright 2003 Marcel Dekker,
Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37
ICT 2012HISTORICAL BACKGROUNDEarl Logan, Jr.Knowledge of
turbomachines has evolved slowly over centuries without thebenet of
sudden and dramatic breakthroughs. Turbomachines, such aswindmills
and waterwheels, are centuries old. Waterwheels, which dip
theirvanes into moving water, were employed in ancient Egypt,
China, andAssyria [1]. Waterwheels appeared in Greece in the second
century B.C. andin the Roman Empire during the rst century B.C. A
seven-ft-diameterwaterwheel at Monte Cassino was used by the Romans
to grind corn at therate of 150 kg of corn per hour, and
waterwheels at Arles ground 320 kg ofcorn per hour [2]. The
Doomsday Book, based on a survey ordered byWilliam the Conqueror,
indicates the there were 5,624 water mills inEngland in 1086.
Besides the grinding of grain, waterwheels were used todrive water
pumps and to operate machinery. Agricola (14941555) showedby
illustrations how waterwheels were used to pump water from mines
andto crush metallic ores in the 16th century [3]. In 1685 Louis
XIV had 221piston pumps installed at Marly, France, for the purpose
of supplying3,200 m3of Seine River water per day to the fountains
of the Versaillespalace. The pumps were driven by 14 waterwheels,
each 12 m in diameter,that were turned by the currents of the Seine
[4]. The undershot waterwheel,which had an efciency of only 30%,
was used up until the end of the 18thcentury. It was replaced in
the 19th century by the overshot waterwheel withan efciency of 70
to 90%. By 1850, hydraulic turbines began to replacewaterwheels
[1]. The rst hydroelectric power plant was built in Germany in1891
and utilized waterwheels and direct-current power
generation.However, the waterwheels were soon replaced with
hydraulic turbines (seeChapter 15) and alternating-current electric
power [6].Although the use of wind power in sailing vessels
appeared inantiquity, the widespread use of wind power for grinding
grain and pumpingwater was delayed until the 7th century in Persia,
the 12th century inEngland, and the 15th century in Holland [5]. In
the 17th century, Leibnizproposed using windmills and waterwheels
together to pump water frommines in the Harz Mountains of Germany
[4]. Dutch settlers brought Dutchmills to America in the 18th
century. This led to the development of amultiblade wind turbine
that was used to pump water for livestock. Windturbines were used
in Denmark in 1890 to generate electric power. Early inthe 20th
century American farms began to use wind turbines to
driveelectricity generators for charging storage batteries. These
wind-electricplants were supplanted later by electricity generated
by centrally locatedsteam-electric power plants, particularly after
the Rural Electric Adminis-Copyright 2003 Marcel Dekker,
Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37
ICT 2012tration Act of 1936 [5]. Today, although a small amount of
electrical poweris generated by wind turbines, most electrical
power is generated by largesteam turbines (see Chapter 8) and gas
turbines (see Part 2 of this chapter).In the second century B.C.
Hero of Alexandria invented rotors drivenby steam [4] and by gas
[7], but these machines produced insignicantamounts of power.
During the 18th and 19th centuries the reciprocatingsteam engine
was developed and became the predominant prime mover
formanufacturing and transportation industries. In 1883 the rst
steamturbines were constructed by de Laval whose turbines achieved
speeds of26,000 rpm [8]. In 1884 a steam turbine, which ran at
17,000 rpm andcomprised 15 wheels on the same shaft, was designed
and built by CharlieParsons. These early steam turbines are
discussed in Chapter 8.The gas turbine was conceived by John Barber
in 1791, and the rstgas turbine was built and tested in 1900 by
Stolze [7]. Sanford Moss built agas turbine in 1902 at Cornell
University. At Brown Boveri in 1903,Armenguad and Lemale combined
an axial-ow turbine and centrifugalcompressor to produce a thermal
efciency of 3% [7]. In 1905 Holzwarthdesigned a gas turbine that
utilized constant-volume combustion. Thisturbine was manufactured
by Boveri and Thyssen until the 1930s. In 1911the turbocharger was
built and installed in diesel engines by Sulzer Brothers,and in
1918 the turbocharger was utilized to increase the power of
militaryaircraft engines [7]. In 1939 the rst combustion gas
turbine was installed byBrown Boveri in Switzerland. A similar
turbine was used in Swisslocomotives in 1942 [10]. The aircraft gas
turbine engine (turbojet) wasdeveloped by Junkers in Germany around
1940.References1. R. L. Daugherty, Hydraulic Turbines, McGraw-Hill,
New York (1920).2. J. Gimpel, The Medieval Machine, Penguin, New
York (1976).3. G. Agricola (trans. by H. C. Hoover and L. H.
Hoover), De Re Metallica,Dover, New York (1950).4. F. Klemm, A
History of Western Technology, Scribner, New York (1959).5. G. L.
Johnson, Wind Energy Systems, Prentice-Hall, New York (1945).6. H.
Thirring, Energy for Man: Windmills to Nuclear Power, Indiana
UniversityPress, Bloomington (1958).7. R. T. Sawyer, The Modern Gas
Turbine, Prentice-Hall, New York (1945).8. A. Stodola, Gas Turbines
Vol. 1, McGraw-Hill, New York (1927).9. G. G. Smith, Gas Turbines
and Jet Propulsion for Aircraft, Atmosphere, NewYork (1944).10. C.
Seippel, Gas Turbines in Our Century, Trans. of the ASME, 75:
121122(1953).Copyright 2003 Marcel Dekker, Inc.113.22.81.34
downloaded 0824709950.pdf at Sat Apr 14 14:09:37 ICT 2012MECHANICAL
AND THERMAL DESIGN CONSIDERATIONSFOR GAS TURBINE ENGINESVedanth
KadambiThis section deals with the fundamentals of mechanical and
thermal designof gas turbine engines. It lays particular emphasis
on the turbine, thoughmany of the statements are general and apply
to compressor design as well.Starting from a description of
thermodynamic and practical cycles used ingas turbine applications,
it deals with the types of engines and theirapplications, the
approach to design (including aerodynamic, secondaryow, thermal and
stress analysis), material selection for various applica-tions, and
mechanical design considerations (turbine disk and blade design,the
secondary ow circuit, and prediction of fatigue life). Finally,
tests fordesign validation and some of the near-term developments
that will improveoverall performance and life are
discussed.Mechanical and Thermal Design ConsiderationsAnOverviewThe
gas turbine industry is often considered as mature since new
large-scaledevelopments are few and the design process is
considered to be wellestablished. In spite of this, the
mechanical/thermal design of a gas turbine isa highly complex
endeavor, costing hundreds of millions of dollars andemploying a
team of several hundred engineers for several years. Duringdesign,
advances are made through increasing levels of sophistication
anddetailed analyses. A full discussion of each of the design
topics would easilyll a volume. A brief presentation will be given
here to serve merely as anoverview of the considerations involved
in the mechanical design of aturbine. The topics to be discussed
are (1) the gas turbine cycle, enginecomponents, and the areas of
applications of gas turbines, and (2)performance, material
selection, durability, and life. The factors involvedin the
aerodynamic, mechanical, and thermal designs, secondary ow,
stressand vibration analyses, life evaluation, etc. will be
considered as well. Testsused to evaluate the performance and
durability of the engine conclude thedesign phase. A discussion of
the directions for future work to improveperformance as well as
life will be provided at the end. The reader shouldleave the
chapter with a global sense of what topics the design engineer
mustaddress. For further details, individual topics should be
studied in greaterdepth from the cited chapters in this book and
literature or fromcomprehensive texts on specic topics.Copyright
2003 Marcel Dekker, Inc.113.22.81.34 downloaded 0824709950.pdf at
Sat Apr 14 14:09:37 ICT 2012The Thermodynamic CycleThe
thermodynamic cycle for the gas turbine engine is the Brayton
cycle,which consists of four theoretical processes. The rst process
is one ofisentropic compression where the pressure of the air drawn
from theatmosphere is raised to the operating level in a
compressor. This constitutesthe work input part of the cycle. The
second is the thermal energy input in acombustoran isobaric
(constant-pressure) process to raise the temperatureof the air to
the highest level permitted in the engine. The third and
fourthprocesses are, respectively, an isentropic expansion (work
output) in theturbine and an isobaric cooling process (energy
rejection to the atmosphere),to complete the cycle. The ideal
thermal efciency of the cycle is given by theexpression [1, 2]ZB 1
1=Pr
g1=g1It is seen that the thermal efciency of the Brayton cycle
is the same as thatof the Carnot cycle with the same isentropic
compression ratio. Never-theless, its thermal efciency for
operation between the same temperaturelimits is lower than that of
the Carnot cycle. The efciency increases as thepressure ratio
increases. For this reason, efforts are made to operate theengine
at as high a pressure ratio as possible.The work output of the
theoretical Brayton cycle is a function of themaximum temperature
in the cycle, the temperature of energy rejection, andthe pressure
ratio. There exists an optimum pressure ratio at which the
workoutput becomes a maximum. The pressure ratio for maximum work
outputis given by the expressionPropt T3=T1g=2g1 Pr1=22The
corresponding maximum work output of the Brayton cycle isWmax CpT1
T3=T11=2 1h i23Engines may be designed to operate close to this
condition. The thermalefciency of the Brayton cycle operating at
the optimum pressure ratio isZBopt 1 T1=T31=24Components of the Gas
Turbine EngineFigure 1 shows the main components of the gas turbine
enginethecompressor, the combustor, and the turbine. Work input
occurs in aCopyright 2003 Marcel Dekker, Inc.113.22.81.34
downloaded 0824709950.pdf at Sat Apr 14 14:09:37 ICT 2012compressor
with several axial and/or centrifugal stages. The engine shown
inFig. 1 has only centrifugal compressors. (Figure 8 shows an
engine withaxial and centrifugal stages for compression.) The
pressure ratio incommercial aircraft engine compressors is often in
the range of 1025,though some experimental engines have pressure
ratios in the range 1735.The turbine driving the compressor is
usually an axial-ow device though insmall engines (auxiliary power
units, or APUs), it is often a radial inwardow device. Energy
addition as heat and a slight pressure drop (35%) occurin a
combustor where a ne spray of fuel burns in the air from
thecompressor. The maximum temperature of the gas is limited by
materialconsiderations, being 22002500 8F in most engines. The
mixture of burnedfuel and air at a high temperature enters the
turbine. Work output is due tothe expansion of the gas while owing
over the rotating turbine blades.Thermal energy rejection from the
engine, as in all practical propulsionengine cycles, occurs due to
the gas that is exhausted from the turbine to theatmosphere. There
is no heat exchanger to reject thermal energy at constantpressure
from the system.In aircraft engines, the air owing through a
propeller or a fan drivenby the turbine gives rise to the
propulsive force on the aircraft. For example,in propeller-driven
engines, the change in momentum of the air owingthrough the
propeller causes a reactive force, resulting in a forward thruston
the engine. In engines with fans, the reactive force is due to the
exhaustjet at the exit of the turbine. Power generation units use
the turbine outputto drive a gearbox or a load compressor.Real Gas
Engine CycleThe real engine cycle differs from the theoretical
Brayton cycle in severalrespects. First, the processes of
compression and expansion are notisentropic. So the work input
needed at the compressor is higher than inFigure 1 Cross-section
showing the main components of a gas turbine engine.Copyright 2003
Marcel Dekker, Inc.113.22.81.34 downloaded 0824709950.pdf at Sat
Apr 14 14:09:37 ICT 2012the theoretical cycle and the work output
of the turbine is lower than in thetheoretical cycle. (In most gas
turbines used for propulsion, the adiabaticcompressor efciency
ranges from 0.83 to 0.88. In turbines the adiabaticefciency ranges
from 0.85 to 0.92.) In addition, there are pressure
lossesassociated with ow through the combustor and several other
parts of themachine. These as well as other deviations from
ideality reduce the net workoutput and the thermal efciency as
compared with that of the theoreticalBrayton cycle. For engines
with a pressure ratio in the range of 1315, thetypical thermal
efciency for operation at 2000 8F is about 35%. A measureof thermal
efciency is the specic fuel consumption, SFC, which is the rateof
fuel consumed (lbm/hr) per unit of output. For efcient operation,
it isnecessary to have as low a fuel consumption and, hence, as low
an SFC aspossible. Reduction in SFC may require an increased inlet
temperature orthe use of a recuperator (a heat exchanger inserted
between the compressorand the combustor). The recuperator transfers
part of the thermal energy ofthe exhaust gases to the high-pressure
air entering the combustor andreduces the fuel consumption. The
engine cycle that uses a recuperator iscalled the regenerative
Brayton cycle [2]. The thermal efciency of the idealregenerative
cycle tted with a recuperator where there are no pressuredrops is
given by the expressionZR 1 Prg1=g=Tr 5Unlike the ideal Brayton
cycle without regeneration, the thermal efciencyof this cycle
diminishes with increasing pressure ratio. However, it
increaseswith increasing temperature ratio as in the Carnot
cycle.Gas Turbine Engine ApplicationsThe following are the areas of
use of gas turbines:1. Propulsion of aircraft as well as
ground-based vehicles. There existfour types of gas turbine
engines: the turboprop, the turbofan, theturbojet, and the
turboshaft, based on their use in propulsion. The rstthree are
designed for use where thrust is important. The turboprop uses
apropeller to move large masses of air and has a low specic thrust.
Itoperates at relatively low Mach numbers, usually on the order of
0.25.(There are some engines that run at higher Mach numbers, on
the order of0.6.) Figure 2 exhibits a typical turboprop engine
manufactured byHoneywell Engines & Systems. Turboprops usually
range in power between600 and 6000 HP. Turboprops used in both
commercial and militaryapplications are relatively small compared
with turbofans, which employhigh-speed fans to move the air.The
turbofan requires large masses of air ow, though only a
fraction,Copyright 2003 Marcel Dekker, Inc.113.22.81.34 downloaded
0824709950.pdf at Sat Apr 14 14:09:37 ICT 2012between 1535%, ows
through the turbine. The rest of the ow passingthrough the fan
expands in an annular nozzle to provide thrust. It operatesat
higher Mach numbers, 0.50.8. The turbofans produced by
HoneywellEngines & Systems have thrusts in the range 1,300 lbf
to 9,000 lbf, a typicalengine being shown in Fig. 3. Such engines
are used in executive jets,commercial aircraft, and military
applications. Pratt & Whitney, GeneralElectric, and Rolls Royce
Plc typically produce engines with thrusts rangingto 20,000 lbf.
The biggest turbofans manufactured have thrusts ranging to100,000
lbf. For turbofans, SFC is expressed as the rate of fuel
consumptionper unit of engine thrust (lbm/lbf.hr). Typical values
of thrust SFC rangebetween 0.35 and 0.6 lbm/lbf.hr depending on the
type of engine and itsoperating condition. The turbojet has a
relatively low mass ow comparedwith turbofans. Its thrust is due to
the acceleration of the uid expanding ina nozzle at the exit of the
turbine. Hence, it has a high specic thrust.Turboshaft engines are
employed in applications where it is necessaryto deliver power to a
low-speed shaft through a gearbox. They are used forcommercial,
military, rotorcraft, industrial, and marine applications andrange
in power from 400 to 4,600 HP. For turboshafts, SFC is expressed
inow rate per HP of output, typical values being in the range of
0.30.5 lbm/Figure 2 Turboprop engine, TPE 331-10U (Honeywell
Engines & Systems).Copyright 2003 Marcel Dekker,
Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37
ICT 2012HP.hr. The U.S. armys main battle tank, Abrams M1A1, is
propelled bythe AGT1500 turboshaft engine, rated at 1,500 HP. It is
tted with arecuperator and operates on the regenerative Brayton
cycle. Here, thewheels are directly driven through a
speed-reduction gear train to reduce therotational speed from about
22,000 rpm (power turbine) to 3,000 rpm at thewheels. A new
recuperated turboshaft engine, LV100, is currently in designat
Honeywell Engines and GE Aeroengines to drive future Abrams
andCrusader battle tanks.2. Auxiliary power units (APUs), Fig. 4.
These are small engines(1001,100 HP) used for air conditioning and
lighting purposes in regional,executive, narrow, and wide-body
commercial as well as military aircraft.They are also used to
propel ground carts. As opposed to turbofan andturboprop engines
that have axial compressor and axial turbine stages, thesemay have
only centrifugal compressors and radial inow turbines.3. Marine
applications. These include Fast Ferry transport engines,Ocean
Patrol, and Hovercraft.4. Industrial turbo-generators. These may
range from small enginesproducing only 75 kW to 20 MW or more for
power production.Figure 3 Turbofan engine, TFE731-60 (Honeywell
Engines & Systems).Copyright 2003 Marcel Dekker,
Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37
ICT 2012Microturbines, which are small industrial turbogenerators
used forlighting and other applications in small buildings,
workshops, and shoppingcomplexes are produced by Honeywell Engines
& Systems as well as a fewothers. General Electric Co.
manufactures gas turbines for large powerproduction. Siemens
Westinghouse Power Corporation has built largeengines with outputs
in the range of 30100 MW. In addition, the companyhas built some
engines as large as 300 MW or more in power output.Design
GoalsOverview. In a broad sense, the design goal is to comply with
all of thecustomers specications while minimizing cost. The
customer species theminimum standards for performance (power output
or thrust, fuelconsumption or thermal efciency), the maximum
permissible weight, andthe expected life or durability of the
engine. Durability is usually specied interms of the number of
cycles of operation or the number of ight hours thatthe engine will
experience during its expected life. Regulatory agenciesimpose
environmental requirements relating to noise levels in
aircraftapplications and the permitted maximum levels of emissions
(oxides ofnitrogen, sulfur, etc). The importance of these
individual requirementsvaries from application to application, as
shown in Fig. 5. The regionsindicated with light gray shade in the
diagram are of high importance foreach application. For example, in
the design of commercial propulsionFigure 4 Auxiliary power unit,
APU131-9 (Honeywell Engines & Systems).Copyright 2003 Marcel
Dekker, Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14
14:09:37 ICT 2012engines, cost, performance, durability (expressed
in mission life cycles),weight, and engine noise levels are
important items to be considered. Formilitary applications, the
important items are performance and weight. Theregions with
medium-dark shading are of intermediate importance, whileregions
with dark shading indicate items of little concern. As seen from
thediagram, cost is of great concern in most applications. In
militaryapplications, cost and long life are sometimes not as
important as theachievement of very high levels of
performance.Since APUs have relatively small outputs and are not in
continuoususe, performance may not be a major consideration in
their design. In allother engines, performance plays an important
role. The main factorsaffecting performance are (1) thermodynamic
cycle (maximum operatingpressure, turbine inlet temperature, and
ambient conditions), (2) aero-dynamic efciencies of the compressor
and turbine vanes and blades(depend on airfoil loads, ow path
losses, etc.), (3) losses in the combustordue to incomplete
combustion, (4) losses due to installation effects, tipclearances,
etc., (5) losses due to secondary ow, and (6) thermal energylosses
from the turbine case to the surroundings. Of these, thermal losses
arenot highly signicant, so that the engine is treated as an
adiabatic device inmost calculations.Figure 5 Design goals and
their dependence on application.Copyright 2003 Marcel Dekker,
Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37
ICT 2012Durability. The mechanical and thermal design of turbine
componentsfocuses on providing the least expensive unit to satisfy
performanceobjectives without failure. Under normal operating
conditions, thecommon failure modes of concern to the designer are
low cycle fatigue,high cycle fatigue, creep, mechanical distortion,
oxidation, corrosion, anderosion. For short-duration emergency
conditions, one must also avoidovertemperature and overstress
failures caused by speed and temperatureexcursions beyond the
normal operating levels. Based on a study of a largenumber of
engines, the USAF has identied the primary causes of
enginefailures, shown in Fig. 6.Predicting a safe life limit
requires an understanding of how theturbine is being used. The
customer species the operating conditions andthe number of cycles
as well as the type of operation expected of the engine.As
previously seen in Fig. 5, the operating life changes from
application toapplication and varies with the number of cycles of
operation as well asother factors. It is critical, therefore, to
understand the customersrequirements before starting the design of
the turbine. To illustrate thispoint, two types of representative
operating cycles are exhibited in Figs. 7(a)and 7(b). Figure 7 (a)
portrays the schematic of an operating cycle that mayapply to
commercial aircraft operation. Here, the engine starts at
groundidle conditions and then accelerates to take-off (100%
power). Usually, thespeed drops about 1520% as the aircraft reaches
its cruising altitude. Fromhere onwards, there may be only small
changes in speed and turbine-inletFigure 6 U.S. Air Force study of
causes of engine failure.Copyright 2003 Marcel Dekker,
Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37
ICT 2012temperature for a long time, after which a quick drop in
speed to idle occursduring landing. The complete operation from
start to nish constitutes onemission cycle. Major variations in
speed and output occur only a few timesduring the entire operation
and only small speed changes occur during themajor part of the
ight. The associated temperature changes and thermalcycling during
ight are thus small. Hence, the materials of the engine arenot
continuously subjected to cyclic temperature changes that cause
thermalfatigue. Figure 7(b), on the other hand, represents an
operating cycle withcyclic and sudden large variations in speed.
Often, the operating conditionsfor a military trainer aircraft or a
tank engine resemble this cycle. The initialpart of the operation
resembles that of Fig. 7(a) until cruising speed isreached. From
here onwards, there are several cycles of rapid speed increaseand
decrease, so that the local material temperatures uctuate
considerablyFigure 7(a) Schematic operating cycle for long-range
commercial ights.Figure 7(b) Schematic operating cycle with large
speed variations.Copyright 2003 Marcel Dekker, Inc.113.22.81.34
downloaded 0824709950.pdf at Sat Apr 14 14:09:37 ICT 2012with time
during ight. Such a type of operation may result in failures due
tolow cycle fatigue discussed below.Two of the main causes of
failure seen in Fig. 6 are fatigue andpreexisting defects, each
accounting for 25% of the total. Fatigue can be oftwo types, low
cycle fatigue (LCF) and high cycle fatigue (HCF). Low cyclefatigue
occurs with the repeated stressing of a component until
cracksinitiate and then propagate to failure. The type of stress
depends of courseon the part. For example, a cooled turbine blade
experiences centrifugalstresses from spool rotation, thermal
stresses from temperature gradientswithin the blade, and stresses
due to varying aerodynamic pressuredistribution. An engine that
undergoes many cyclic excursions in a ight,such as the application
portrayed in Fig. 7(b) above, should be designed toresist LCF well.
Cracks may occur in a part not only from LCF initiation,but also
from preexisting defects. High cycle fatigue results from
vibrationat speeds close to resonance in one of the components,
e.g., blades. Suchstresses alternate around a mean value and are
purely mechanical. They arecaused by a forcing function driving the
component at a frequency matchinga natural frequency of the part.
The forcing function could, for example, bean imbalance, or a
pressure pulse. The wakes of a vane causing pressureuctuations on
the downstream rotating blade are an example of a pressurepulse.
Also, a part can undergo uttera vibration phenomenon in whichthe
displacement of a part due to aerodynamic loading causes a change
inthe load, which in turn allows the displacement to relax to its
original format which point the load starts again. Although the
alternating stresses maybe much lower than the background stress,
the frequencies are high and alarge number of cycles can be
accumulated quickly. A Goodman diagram(Fig. 16; see section on
thermal/stress analysis and life prediction) or one ofits variants
is used to assess if the combined alternating and
steady-statestress levels are acceptable.Preexisting defects are
often due to small amounts of foreign materialor imperfections in
the disk or any other component. These imperfectionsact as areas of
stress concentration and cause failures even when theaverage stress
is well below the yield limit in most areas. Sometimes, smallcracks
exist, especially in large castings. These, too, cause local high
stressesthat may lead to failure. Life prediction is then a matter
of calculating howrapidly such a aw will grow until the part fails.
To guard againstpreexisting defects, X-ray pictures may be taken to
determine whetherinternal aws or cracks exist in large specimens.
Ultrasound and othertechniques are also used. If judged as serious,
parts with aws arediscarded.Excessive creep and stress-rupture are
the third and fourth majorcauses, each accounting for approximately
12.5% of all failures. Creep refersCopyright 2003 Marcel Dekker,
Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37
ICT 2012to the continuous extension of a highly stressed material
subjected toelevated temperatures for long periods of time. Creep
is a function ofmaterial properties, the level of stress, the
temperature, and its duration.Depending on the part, the normal
design philosophy is to limit the averagestress to a level such
that the strain due to creep is below 1% to 2% over theexpected
life of the component. Stress-rupture [3] is the ultimate failure
of apart due to creep. Different materials will undergo different
amounts ofcreep elongation before rupture. Stress-rupture may occur
with almost nonoticeable creep or with considerable elongation
depending on the material,the stress, and the temperature. Blades
and blade roots or attachments at thedisk are subject to
stress-rupture. Improper design procedure andnonisotropic material
properties have often been responsible for thesefailures. It is
necessary to have a good knowledge of all the expected
stresses(thermal and mechanical) and material properties if such
failures are to beavoided.Factors that are somewhat difcult to
control are (1) corrosion anderosion resulting in damage to parts
along the ow path, especially theleading edges of vanes and blades,
(2) damage due to foreign objects likebirds hitting fan or
compressor blades during ight, and (3) controlmalfunction.
Unfortunately, the effects of corrosion depend strongly on
thepollutants in the atmosphere as well as on the fuel, which may
contain sulfuror compounds of alkaline materials. These are hard to
control and mayrequire surface coatings that prevent contact
between the hot gases and thesurface (see discussion at the end of
section on thermal/stress analysis andlife prediction). The impact
of foreign objects like birds, tire treads, gravel,and ice or hail
on fan blades and the immediately following compressorstages can be
severe. It is necessary to ensure that the engine can withstandsuch
types of impact without failure. (See discussion related to
birdingestion or foreign object damage tests near the end of this
chapter.) Toreduce the probability of control malfunction, it is
necessary to build acertain amount of redundancy in the system, so
that if one of the controlsfails for some reason, there is another
control that will perform the requiredoperation. Experience is the
guide in determining the degree of redundancynecessary to minimize
the probability of failure.Thermal and Mechanical Design
ApproachThe design of a gas turbine consists of four main phases.
In the rst, amarketing study determines the need of the customer
for a proposed engineand a conceptual study is performed to assess
the feasibility that an enginecan protably be designed and
developed to satisfy this need. The second isthe preliminary design
phase. In preliminary design, projections fromCopyright 2003 Marcel
Dekker, Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14
14:09:37 ICT 2012experience and existing similar designs are used
to lay out the ow path, thevelocity triangles at the compressor and
the turbine stages and to makeinitial drawings of the proposed
engine. The materials needed for variouscomponents are also picked
on a preliminary basis. The choice of materialsis based on
experience and expected conditions of operation. These choicesare
subject to change based on the detailed analyses (thermal and
stress) thatoccur later. Finally, rst estimates of performance and
secondary ow areobtained. Each company will have different criteria
regarding the level ofdetail required before one can exit the
preliminary design phase and enterthe third phase, detailed design.
The detailed design will perform all detailedanalyses and life
predictions to exit with completed component drawings.Each phase
will have design reviews to ensure that the design is ready
toproceed to the next level. In the fourth phase, the parts are
procured, anengine is built, and qualication tests are performed.
This phase is completewith certication by the regulatory
agencies.During design it is necessary to optimize the performance,
the choiceof materials, and the proposed manufacturing methods to
satisfy liferequirements and at the same time to minimize the cost.
Thus, design isbased on compromises affecting materials,
manufacturing methods (castingas opposed to forging, welding as
opposed to brazing, etc.), the levels ofsecondary ow, and operating
temperatures. Itemized below are the mainitems for consideration in
design.1. Material selection and types of materials used: Different
materialsare used for different components of the engine, depending
on thetemperatures, stress levels, and expected service lives.
Inexpensive and lightmaterials are used for the front casing around
the fan and the rst few axialcompressor stages not subjected to
high temperatures. More expensive andstructurally strong highly
temperature-resistant materials are used in therotating parts of
the turbine. Table 1 is a partial list of the types of
materialsused and Table 2 lists the considerations for material
selection. Many partsTable 1 Typical Materials Used in Propulsion
Gas TurbinesComponent type Fan Compressor
TurbineRotating,componentsTitaniumAluminumTitanium
SteelAluminumNickel-based alloysStatic components Titanium Steel
Steel TitaniumAluminumMagnesium alloyNickel-based
alloysCobalt-based alloysSteelCopyright 2003 Marcel Dekker,
Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37
ICT 2012of the turbine are made of alloys of nickel, those used
commonly beingHastalloy, Inconel, and Waspalloy for
compressor/turbine casings, shafts,and other areas. Blades and
vanes are routinely made of single-crystal,directionally solidied,
or equi-axed alloys of various compositions.Waspalloy or Inconel
may be used also to make seal plates for turbinediscs. In some
experimental engines, turbine discs and some seal plates aremade of
sintered alloys of nickel. Some of them are capable of
withstandingextremely high temperatures, running as high as 1,450
8F.2. Aerodynamic design: This involves the denition of the
airfoilcontours, both of the compressor and of the turbine stages.
The design startswith the velocity triangles laid out during
preliminary design. The bladeangles should match the inlet and exit
angles specied by the velocitytriangles. The contour of the blade
is then designed to provide a smoothow and to ensure that there is
little separation at all points on the blade.Proper turning of ow
over the blade and the contour design ensure thatblade loading is
as desired. Usually, HPT blades turn out to be somewhatthicker at
the leading edge than LPT blades. In addition, they do not
exhibitlarge radial twists. The design of compressor airfoils
(refer to Chapter 6) isdifferent from that of turbine airfoils
(refer to Chapter 7). This is due to theTable 2 Materials Selection
CriteriaFailure modes CostManufacturingprocess ormode offabrication
Weight OthersStrength athightemperatureMaterial cost Casting
Density
Containment(ductility,strength)Low-cyclefatiguestrengthFabricationcostHardness
andease
ofmachiningStrength/weightThermalexpansionHigh-cyclefatiguestrengthVendoravailabilityForging
ThermalconductivityCreep strength Repairability Specic heatFast
fracture,cyclic crackgrowth rate Availability Corrosionresistance
Consistency,cleanliness ofproduct Copyright 2003 Marcel Dekker,
Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37
ICT 2012adverse pressure gradient against which the uid has to move
in acompressor. The adverse pressure gradient tends to cause ow
separationand high levels of aerodynamic losses unless the turning
angles of the bladesare quite low. In the turbine blade where the
pressure gradient is favorable,the ow can be turned through large
angles (12081308), without fear ofseparation. Large amounts of work
output can be obtained with just one ortwo stages in the turbine,
while to compress the air through the samepressure ratio, several
axial stages (each with a small pressure ratio) may beneeded. For
this reason, it is the common practice in several companies touse
centrifugal stages that permit larger pressure ratios per stage
than axialcompressors. In addition, they are more durable than
axial stages. It should,however, be remembered that centrifugal
impellers are of large diameter andpermit lower mass ow in relation
to their size than axial stages and henceadd considerably to the
engine weight.3. Secondary air-ow design: The search for higher and
higherthermal efciencies has led to ever-increasing temperatures at
the turbineinlet, on the order of 2,600 8F in modern propulsion
engines. In severalmilitary engines and in some experimental
engines, this temperature ishigher by several hundred degrees. The
gas emerging from the combustorhas both circumferentially and
radially varying temperatures, the maximumof which may be 2040%
higher than the average temperature. Thematerials subjected to
these temperatures may suffer serious deterioration inmechanical
properties (yield stress, ultimate stress, fatigue limit, etc.).
Inaddition, operation at high transient temperatures leads to
thermal stressesand fatigue. It is therefore necessary to maintain
metal temperatures lowenough so that property deterioration and
thermal fatigue do notsignicantly affect the life of the component.
To this end, relatively coolair at the required pressure is
channeled to the component where cooling isneeded. Most of the
cooling air is usually drawn from the plenum aroundthe combustor
(see Fig. 1), referred to as Station 3. Other lower-pressuresources
such as impeller blade exit (Station 2.7) and the entry to
thecentrifugal compressor (Station 2.5) are employed in addition to
Station 3.In some engines, for cooling shrouds and areas of low
pressures, air may bedrawn from still-lower pressure sources (e.g.,
the fan exit or an intermediateaxial stage). In modern turbines,
the total secondary ow may range from8% to 22% or more of the total
core ow. The cooling requirements of theHPT nozzle and blade, the
HPT disk, and purge air for HPT cavitiesconstitute a major fraction
of the air drawn from the combustor plenum.Some of it may be used
for thrust balancing, and sometimes to cool the LPTdisk and blade
as well. Air for LPT cooling and seal buffer often comes
fromsources such as the inlet to the impeller or an axial
compressor stage.Secondary ow design therefore initially requires a
decision on theCopyright 2003 Marcel Dekker, Inc.113.22.81.34
downloaded 0824709950.pdf at Sat Apr 14 14:09:37 ICT
2012appropriate source for each of the cooling circuits, since the
air drawn offthe compressor does not ow over all the turbine
blades. There is a greaterdeterioration in turbine output due to
air drawn from high-pressure stagesas compared with air drawn from
low-pressure stages. So, every effortshould be made to draw air at
the lowest possible pressure to provide therequired cooling effect.
After these decisions are made, it is necessary tocalculate the
pressure drops, the clearances at labyrinth and other seals, andthe
sizes of orices needed to meter the ow in each circuit.Secondary
air serves the following main purposes in the turbine.a. Provide
cooling air to critical temperature-limited components.This is
indeed the main purpose of secondary ow design. The provision
ofcavity purge ow (to prevent hot gas ingestion) may be included in
the samecategory, as it ensures that the disk cavities are
maintained at sufcientlylow temperatures for long life. Figure 8
depicts a typical turbofan engine ofa low thrust class along with
its secondary ow circuit, which draws air fromseveral sources. At
the front of the engine is the fan, which is a compressorstage of
small pressure ratio (not shown in Fig. 8). The fan is followed
byfour axial compressor stages and a centrifugal stage. The rst
turbine stage(high-pressure turbine, HPT) drives the centrifugal
compressor. The low-pressure stages of the axial compressor
(low-pressure compressor, LPC), aredriven by the low-pressure
turbine (LPT), which may consist of two or morestages. The main
secondary ow stream is drawn from the combustorplenum to cool the
liner of the combustion chamber, the rst HPT nozzle,Figure 8
Cross-section of a typical turbofan engine indicating secondary
owstreams.Copyright 2003 Marcel Dekker, Inc.113.22.81.34 downloaded
0824709950.pdf at Sat Apr 14 14:09:37 ICT 2012and its attachments.
A substantial fraction of the ow passes through theTOBI (tangential
on-board injector). This may be a set of nozzles or anappropriately
drilled set of holes designed to increase the tangential velocityof
the air. The air emerging from the TOBI has a low static
temperature anda tangential velocity that approximates that of the
rotating disk. Hence, itcools the turbine disk and the blade and
purges the HP turbine cavities aswell. The second stream drawn from
the impeller exit (marked HP in thediagram) ows down the back face
of the impeller. It may be used to coolthe bore of the turbine and
for bearing cooling purposes where possible. Inthe illustration, it
is used partly to cool the rst LPT disc. Still anotherstream drawn
from the impeller inlet ows axially through the impeller boreto
purge the second and the third LPT disk cavities.b. Provide buffer
air to bearing seals. This is the second importantpurpose of
secondary ow design. It is necessary to provide a sufcientpressure
difference between bearing seal faces so that oil leakage
isminimized. The air used for buffering should be at temperatures
not higherthan 400 8F since the oil coming in contact with the air
tends to coke andform hard deposits if its temperature becomes
excessive.c. Maintain bearing thrust loads at low levels/thrust
balance. Thethrust on the turbine disk due to aerodynamic and other
loads acts on theshaft bearing. The bearing should be designed to
withstand the thrust sothat the shaft is held in place. The larger
the bearing load, the bigger andmore expensive the bearing becomes.
By using a thrust piston arrangement,secondary air at the
appropriate pressure is made to exert a force on the diskto reduce
the net thrust on the bearing. Thrust load calculation is a
detailedbookkeeping effort to account for all the aerodynamic
forces, momentumchanges, and pressure forces acting on the surfaces
of a control volume.Since the calculations involve differences
between large numbers of similarmagnitudes, there is a considerable
amount of uncertainty in the estimatednet thrust. It may therefore
be necessary to design the bearing to withstand
alarger-than-calculated load. In some cases, the calculations may
lead to avery small estimate for the thrust load. Then, secondary
ow may be used toensure that the load acts in only one direction
and does not reverse due tochanging operating conditions. It is a
good practice to check the thrust onthe bearing at several
operating conditions, say full power, 50% power, andidle
conditions, to ensure that there is no thrust reversal in the
operatingrange. Secondary ows have also been used to reduce the
loads and thus thestresses acting on nozzles and such other
components in some experimentalengines. (For details regarding
secondary ow design, see the chapter byBruce Johnson.)d. Cooled and
uncooled airfoil design. Airfoils may be cooled oruncooled
depending on the temperature of the gas and the material of
theCopyright 2003 Marcel Dekker, Inc.113.22.81.34 downloaded
0824709950.pdf at Sat Apr 14 14:09:37 ICT 2012airfoil. The uncooled
airfoil operates at relatively low temperatures, issimpler to
design, and can employ standard materials. It has a low cost,though
its growth potential is limited to simple material substitutions.
It iseasier to manufacture and is tolerant to some manufacturing
deviations.While it is possible to obtain lower temperatures with a
cooled design andthus ensure a long life even with high gas
temperatures, the design is morecomplex and takes longer to
complete. The manufacturing processes arevery complicated and are
less tolerant to deviations. The cost of the airfoil ismuch higher.
Nevertheless, the design provides greater exibility and
futuregrowth potential. In addition, with the current levels of
turbine inlettemperatures, it is impossible to nd a material that
can satisfy the cyclic liferequirements with no cooling and, hence,
it is quite justiable to incur theextra cost and effort to design a
cooled airfoil.A signicant fraction of the secondary ow is used for
turbine airfoilcooling. The maximum operating temperature for the
airfoil depends on thematerial used and may be as high as 1,900 8F.
The cooling ow enters thepassages in the blade root and passes
through narrow channels in theinterior of the airfoil I (see cross
section, Fig. 10), designed to suit the airfoilsize and shape. In
turbines operating at high temperatures, even with thebest
heat-transfer augmentation techniques, internal convection
alonecannot maintain airfoil temperatures below 1,8001,900 8F. It
is thennecessary to provide a lm of cool uid on the outer surface
to reducecontact between the hot gases and the metal. This lm is
obtained byejecting part of the cooling air through lm-holes at
critical locations wherehigh metal temperatures are expected. If
shower-head lm cooling is used, afraction of the cooling ow exits
through lm-holes at the airfoil leadingedge. Some lm-holes may also
be provided on the pressure and the suctionsurfaces. Another
fraction exits at the trailing edge and a small amount maybe
ejected at the blade tip through nearly radial holes. The lm-holes
keepthe leading-edge and the near-stagnation regions of the
pressure and suctionsurfaces cool, while the air ejected along the
trailing edge cools the rest ofthe these surfaces. Figure 9 shows a
cooled blade with showerhead andpressure surface lm-holes used in
turbines.Having dened the airfoil surface (the outer shape of the
blade whereit is exposed to gas), the next step is the cooling
passage design to maintainthe blade surface at temperatures
commensurate with its material propertiesand expected life. Due to
material property limitations, this temperaturedoes not exceed
1,8001,9008F in most designs. The cooling passages areoften
serpentine and may have trip-strips or ns in them for
heat-transferenhancement. Further, where shower head cooling holes
are required, thecooling air is made to impinge on the inner
surface of the leading edgeCopyright 2003 Marcel Dekker,
Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37
ICT 2012before emerging at the surface. All these features are
indicated in Fig. 10,which shows a schematic diagram of the airfoil
internal passages.The parameters affecting cooled blade design are
(1) blade materialcharacteristics and cost, (2) airfoil shape, (3)
required cooling ow and thetrailing-edge thickness, (4) allowable
stress levels, (5) number of blades, and(6) vibratory environment.
Minimizing the cooling air required for theairfoil is an important
consideration in design. Cooling air ow (ejected atlm-holes,
trailing edge, etc.) and blade rotation generally affect (1)
theaerodynamics of the blade and the overall efciency of the
system, (2)impingement heat transfer at the leading edge, and (3)
the local heat transferbehind trip-strips and ns. In addition,
blade-tip thickness and streamlinesat the trailing edge are
affected by the cooling ow issuing at the trailingedge. (For new
designs, it may be necessary to use experience andextrapolate
beyond the range of available data.) At present, CFD analysisdoes
not provide accurate predictions of heat transfer and pressure
drops incooling passages with complicated internal geometry,
especially whererotation is involved. Further, for complicated
situations, considerableexpertise and effort are needed to obtain
solutions by using CFD. Hence, itis difcult to use CFD as a design
tool. Improvements in CFD techniquesFigure 9 Typical high-pressure
turbine blade with shower head and lm-coolingholes.Copyright 2003
Marcel Dekker, Inc.113.22.81.34 downloaded 0824709950.pdf at Sat
Apr 14 14:09:37 ICT 2012and a multidisciplinary computational
approach (see Chapter 9) to optimizethe geometry and cooling ow
requirements may help in this direction. Thiscomputation should
include the external and internal surface details as wellas heat
transfer as variables. A good analysis therefore needs an
accurateestimate of the convective heat-transfer coefcients in the
airfoil passages.Presently, the local heat-transfer coefcients
inside the airfoil may bedetermined by using the liquid-crystal
technique [4, 5], which providesreliable results for stationary
internal cooling passages. The liquid crystal isa material which is
sensitive to temperature and exhibits fringes of variouscolors
(red, green, and blue), at different temperatures. A scale model of
theairfoil (8 to 12 times enlarged) is made of a transparent
material (plexiglass,stereo-lithography, etc.). It can be sprayed
on the inside of the passagewhere thermal data are required. When
hot air is passed through thepassage, the internal surfaces become
warm and the liquid crystal exhibitscolor fringes as a function of
time. The fringes can be recorded on a videocamera and the
transient data analyzed by using a computer. The computerprocesses
the data further to determine the heat-transfer coefcients on
theinside of the blade. Unfortunately, the technique is difcult to
use in arotating environment. Mass transfer technique (sublimation)
may be used asan alternative to liquid-crystal technique for
stationary components.However, the coating of the internal passages
with a sublimating materialFigure 10 Schematic diagram of the
interior of an airfoil with cooling passages.Copyright 2003 Marcel
Dekker, Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14
14:09:37 ICT 2012and the measurement of local heat-transfer
coefcients may pose moredifculties than for the liquid-crystal
test.1. Rotating tip shrouds. Figure 11 portrays schematically
anuncooled LPT blade with a rotating tip shroud. The tip shroud is
necessarydue to the large radius and blade span in the low-pressure
stages. The sameblade-tip clearance will cause a much larger
fraction of leakage at a low-pressure stage than at a high-pressure
stage. The gain in power output andturbine efciency due to the tip
shroud should be balanced against the costand complexity of design.
Tip shrouds may have one or more teethdepending on the permissible
leakage and the required aerodynamicefciency. All the design
parameters for a cooled blade are similar to thoseof the cooled
blade, except the rotating tip shroud and the number of teethon
it.2. Blade-to-disk attachment. There exist two types of
attachmentsbetween the blade and the disk. The rst is the integral
design where theblade and the disk are made of the same material.
These are cast as anintegral unit and cannot be detached. This
design is usually used incompressor and turbine stages in which the
disk stresses are so low that theblade material can stand the
temperature and the stresses. Typically inturbines, a high-strength
forging that has a lower tolerance to temperature isused for the
disk, whereas a material casting that can stand highertemperatures
is used for the blades. In HP turbines where the blade
needscooling, the procedure is to cast the blade as a separate
piece that can beinserted in the rim of the disk at the r tree.
Then the blade can be made ofspecial alloys of nickel with high
strength and tolerance to temperature.Moreover, the blade can be
made with serpentine or other passages throughwhich cooling air can
be passed to maintain the surface at low temperaturesto ensure long
life.3. Turbine disk design. Disk design should ensure that the
stressesdue to thermal transients and those induced by rotation do
not becomeexcessive at any location. The main areas of concern are
the disk rim, theweb, and the disk bore. At the rim, the blade-disk
attachment area (r-tree)is subjected to high stresses due to the
centrifugal forces on the blades. Thedisk rim is heated by
conduction at the blade attachment, by convectionnear the blade
platform, and by the ingested gas in the cavities. It
shouldtherefore be cooled by providing adequate amounts of air at
both faces ofthe disk. The ow should also be sufcient to keep the
disk cavities purgedsuch that gas ingestion is minimized. The main
aspect of the design is toguard against LCF failure. It is
necessary as well to guard against stress-rupture at specic points
(e.g., r-tree attachment), due to excessive creep,thermal, and
bearing stresses. At the disk bore where the stresses oftenexceed
yield limits, it is necessary to guard against the possibility of
failureCopyright 2003 Marcel Dekker, Inc.113.22.81.34 downloaded
0824709950.pdf at Sat Apr 14 14:09:37 ICT 2012Figure 11
Low-pressure turbine blade with a tip shroud.Copyright 2003 Marcel
Dekker, Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14
14:09:37 ICT 2012due to cyclic operation. In addition, disks have
to be designed to operate atspeeds about 20% above the engine
operating speed for maximum power.Referred to as overspeed
capability, this design ensures that in the event theengine needs
extra power during an emergency, there is adequate marginwith
little risk of failure. It also provides safety against
inadvertentoverspeeds.4. Turbine stage design. The design of
turbine stages requiresspecication of the shapes of the airfoils,
the rotational speeds of therotors, the velocity triangles,
aerodynamic efciencies, and the work output.Figure 12 shows
schematics of typical turbine HPT and LPT blades. Sincethese two
blades run at different speeds, have different velocities of gas
ow,and have different outputs, they are quite different in shape.
The primaryelement of aerodynamic design is the maximization of
blade efciency. For agiven stage work output, the stage efciency
increases with tip speed toreach a maximum level at a certain
speed. Efforts are made to design theblade to operate close to this
optimal speed. In the HP turbine stage,because of the high density
and high velocity of the gas, the ow arearequired and the disk
diameter are smaller than those of the LPT. Further,the airfoils
are usually of small span compared with those of the LPT stagesand
turn the gas through large angles ranging to 1308. These
requirements(high tip speed for maximum efciency and small
diameter) imply that theyrun at much higher rotational speeds than
LPT blades. In gas turbinesdesigned by Honeywell Engines &
Systems, there is no attached rotating tipshroud at the HPT blade
tips, since leakage across the blade is not as seriousas in the
LPT. (Large engines designed by Rolls-Royce Plc., for example,often
have rotating tip shrouds on HPT blades as well.) As opposed to
this,the LPT stages have large diameters since they are driven by
low-pressure,low-density gas with large specic volumes. They tend
to run at lower tipFigure 12 Schematic diagrams of typical HP
turbine and LP turbine blades.Copyright 2003 Marcel Dekker,
Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37
ICT 2012speeds as well since their work output is smaller than that
of the HP stage.The span of the blade has to be sufciently large
(high aspect ratio) to passthe gas with low density. In addition,
as compared with HPT blades, theseblades may have more of a radial
twist, to accommodate the changes inincidence angle with increasing
radii. They do not need as much cooling airas the HPT stages since
they deal with cooler gas. Often, LPT blades aredesigned with no
cooling at all, since modern materials can withstandreasonably high
temperatures and still have enough life to satisfyspecications.
Even so, the disks require air to keep their sides cool andto purge
the cavities to prevent gas ingestion. As the temperatures
andspeeds are lower overall, the disks may be made of materials
that aregenerally less expensive and may still be more durable than
the disks of HPTstages. The blades may be provided with rotating
tip shrouds, since theproblem of leakage at the airfoil tip is more
serious at the LPT blades.5. Thermal/stress analysis and life
prediction. The next step in designis the determination of stresses
in the disks, blades, and other criticalcomponents of the
turbomachine. This starts with a nite-element thermalanalysis of
the component including appropriate boundary conditions. Ingeneral,
a commercial code is utilized for mos