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., 1995).Library of Congress Cataloging-in-Publication DataA catalog record for this book is available from the Library of Congress.ISBN: 0-8247-0995-0This book is printed on acid-free paper.HeadquartersMarcel Dekker, Inc.270 Madison Avenue, New York, NY 10016tel: 212-696-9000; fax: 212-685-4540Eastern Hemisphere DistributionMarcel Dekker AGHutgasse 4, Postfach 812, CH-4001 Basel, Switzerlandtel: 41-61-260-6300; fax: 41-61-260-6333World Wide Webhttp://www.dekker.comThe publisher offers discounts on this book when ordered in bulk quantities. Formore information, write to Special Sales/Professional Marketing at the headquartersaddress above.Copyright # 2003 by Marcel Dekker, Inc. All Rights Reserved.Neither this book nor any part may be reproduced or transmitted in any form or byany means, electronic or mechanical, including photocopying, microlming, andrecording, or by any information storage and retrieval system, without permission inwriting from the publisher.Current printing (last digit):10 9 8 7 6 5 4 3 2 1PRINTED IN THE UNITED STATES OF AMERICACopyright 2003 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 Design, Daniel L. Ryan3 Lubrication Fundamentals, J George Wills4 Solar Engineering for Domestic Buildings, William A. Himmelman5 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 Lewis HBell17. Gears and Their Vibration A Basic Approach to Understanding Gear Noise,J Derek Smith18. Chains for Power Transmission and Matenal Handling- Design and Appli-cations Handbook, American Chain Association19. Corrosion and Corrosion Protection Handbook, edited by Philip ASchweitzer20 Gear Dnve Systems Design and Application, Peter Lynwander21 Controlling In-Plant Airborne Contaminants Systems Design and Cal-culations, John D. Constance22. CAD/CAM Systems Planning and Implementation, Charles S Knox23 Probabilistic Engineering Design Principles and Applications, James NSiddall24. Traction Drives Selection and Application, Frederick W Heilich III andEugene E Shube25. Finite Element Methods An Introduction, Ronald L. Huston and Chris E.PasserelloCopyright 2003 Marcel Dekker, Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37 ICT 201226 Mechanical Fastening of Plastics An Engineenng Handbook, Brayton Lincoln,Kenneth J Gomes, and James F Braden27 Lubrication in Practice Second Edition, edited by W S Robertson28 Principles of Automated Drafting, Daniel L Ryan29 Practical Seal Design edited by Leonard J Martini30 Engineenng Documentation for CAD/CAM Applications, Charles S Knox31 Design Dimensioning with Computer Graphics Applications, Jerome CLange32 Mechanism Analysis Simplified Graphical and Analytical Techniques, LyndonO Barton33 CAD/CAM Systems Justification, Implementation, Productivity MeasurementEdward J Preston, George W Crawford, and Mark E Coticchia34 Steam Plant Calculations Manual, V Ganapathy35 Design Assurance for Engineers and Managers, John A Burgess36 Heat Transfer Fluids and Systems for Process and Energy Applications,Jasbir Smgh37 Potential Flows Computer Graphic Solutions, Robert H Kirchhoff38 Computer-Aided Graphics and Design Second Edition, Daniel L Ryan39 Electronically Controlled Proportional Valves Selection and ApplicationMichael J Tonyan, edited byTobi Goldoftas40 Pressure Gauge Handbook, AMETEK, U S 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 Ganapathy48 Solving Mechanical Design Problems with Computer Graphics, Jerome CLange49 Plastics Geanng Selection and Application, Clifford E Adams50 Clutches and Brakes Design and Selection, William C Orthwem51 Transducers in Mechanical and Electronic Design, Harry L Tnetley52 Metallurgical Applications of Shock-Wave and High-Strain-Rate Phenom-ena, edited by Lawrence E Murr, Karl P Staudhammer, and Marc AMeyers53 Magnesium Products Design, Robert S Busk54 How to Integrate CAD/CAM Systems Management and Technology, WilliamD Engelke55 Cam Design and Manufacture Second Edition, with cam design softwarefor the IBM PC and compatibles, disk included, Preben W Jensen56 Solid-State AC Motor Controls Selection and Application, Sylvester Campbell57 Fundamentals of Robotics, David D Ardayfio58 Belt Selection and Application for Engineers, edited by Wallace D Enckson59 Developing Three-Dimensional CAD Software with the IBM PC, C Stan Wei60 Organizing Data for CIM Applications, Charles S Knox, with contributionsby Thomas C. Boos, Ross S Culverhouse, and Paul F MuchnickiCopyright 2003 Marcel Dekker, Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37 ICT 201261 Computer-Aided Simulation in Railway Dynamics, by Rao V Dukkipati andJoseph R Amyot62 Fiber-Reinforced Composites Materials, Manufacturing, and Design, P KMallick63 Photoelectric Sensors and Controls Selection and Application, Scott MJuds64 Finite Element Analysis with Personal Computers, Edward R Champion,Jr and J Michael Ensmmger65 Ultrasonics Fundamentals, Technology, Applications Second Edition,Revised and Expanded, Dale Ensmmger66 Applied Finite 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, and Use in Design, Frank Porter74 Thermal Fatigue of Metals, 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 Meyers, Lawrence E Murr, and Karl P Staudhammer78 Industrial Refrigeration Principles, Design and Applications, P C Koelet79 Applied Combustion, Eugene L Keatmg80 Engine Oils and Automotive Lubrication, edited by WilfriedJ Bartz81 Mechanism Analysis Simplified and Graphical Techniques, Second Edition,Revised and Expanded, Lyndon O Barton82 Fundamental Fluid Mechanics for the Practicing Engineer, James WMurdock83 Fiber-Reinforced Composites Matenals, Manufactunng, and Design, SecondEdition, Revised and Expanded, P K Mallick84 Numencal Methods for Engmeenng Applications, Edward R Champion, Jr85 Turbomachmery Basic Theory and Applications, Second Edition, Revisedand Expanded, Earl Logan, Jr86 Vibrations of Shells and Plates Second Edition, Revised and Expanded,Werner Soedel87 Steam Plant Calculations Manual Second Edition, Revised and Expanded,V Ganapathy88 Industrial Noise Control Fundamentals and Applications, Second Edition,Revised and Expanded, Lewis H Bell and Douglas H Bell89 Finite Elements Their Design and Performance, Richard H MacNeal90 Mechanical Properties of Polymers and Composites Second Edition, Re-vised and Expanded, Lawrence E Nielsen and Robert F Landel91 Mechanical Wear Prediction and Prevention, Raymond G BayerCopyright 2003 Marcel Dekker, Inc.113.22.81.34 downloaded 0824709950.pdf at Sat Apr 14 14:09:37 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 Engi-neenng Applications, Edward Miller102. Practical Fracture 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