Intended Audience

This book is intended to provide a foundation for the analysis and design of aircraft engines. The target audience for this book is upper classmen, undergraduates, and first-year graduate students in aerospace and mechanical engineering. The practicing engineers in the gas turbine and aircraft industry will also benefit from the integration and system discussions in the book. Background in thermodynamics and fluid mechanics at a fundamental level is assumed.

Motivation

In teaching under graduate and graduate propulsion courses for the past 23 years, I accumulated supplemental notes on topics that were not covered in most of our adopted textbooks. The supplemental materials ranged from issues related to the propulsion system integration into aircraft to the technological advances that were spawned by research centers around the world. I could have continued handing out supplemental materials to the textbooks to my classes, except that I learned that the presentation style to undergraduate students had to be (peda-gogically) different than for the graduate students. For example, leaving out many steps in derivations of engineering principles can lead to confusion for most undergraduate students. Although it is more important to grasp the underlying principles than the mechanics of some derivations, but if we lose the students in the derivation phase, they may lose sight of the underlying principles as well. Another motivation for attention to details in analysis is my conviction that going back to basics and showing how the end results are obtained demystifies the subject and promotes students’ confidence in their own abilities.

Mathematical Level

The mathematics in the present book is intentionally kept at the calculus and basic differential equations level, which makes the book readily accessible to undergraduate engineering students. Physical interpretations of mathematical relations are always offered in the text to help students grasp the physics that is hidden and inherent in the formulas. This approach will take the mystery out of formulas and let engineering students go beyond symbols and into understanding concepts.

Chapter Organization and Topical Coverage

The first chapter is an introduction to airbreathing aircraft engines and is divided in two parts. The first part reviews the history of gas turbine engine development, and the second part highlights modern concepts in aircraft engine and vehicle design. Young engineering students are excited to learn about the new opportunities and directions in aircraft engine design that are afforded by advances in materials, manufacturing, cooling technology, computational methods, sensors, actuators, and controls. Renewed interest in hypersonicair breathing engines in general and supersonic combustion ramjets in particular as well as a sprawling interest in Uninhabited Aerial Vehicles (UAVs) has revitalized the ever-popular X-planes. The goal of Chapter 1 is first to inform students about the history, but more importantly to excite them about the future of aerospace engineering.

Chapter 2 is a review of compressible flow with heat and friction. The conservation principles are reviewed and then applied to normal and oblique shocks, conical shocks, and expansion waves, quasi-one-dimensional flows in ducts as well as Rayleigh and Fanno flows. At the closing of Chapter 2, the impulse concept and its application to gas turbine engine components are introduced.

Chapter 3 is on engine thrust and performance parameters. Here, we introduce internal and external performance of aircraft engines and their installation effect.

Chapter 4 describes aircraft gas turbine engine cycles. The real and ideal behaviors of engine components are described simultaneously in this chapter. Efficiencies, losses, and figures of merit are defined both physically and mathematically for each engine component in Chapter 4. Once we define the real behavior of all components in a cycle, we then proceed to calculate engine performance parameters, such as specific thrust, specific fuel consumption and thermal and propulsive efficiencies. The ideal cycle thus becomes a special case of a real cycle when all of its component efficiencies are equal to one.

The next five chapters treat aircraft engine components. Chapter 5 deals with aircraft inlets and nozzles. Although the emphasis throughout the book is on internal performance of engine components, the impact of external or installation effects is always presented for a balanced view on aircraft propulsion. As a building block of aircraft inlet aerodynamics, we have thoroughly reviewed two-dimensional and conical diffuser performance. Some design guidelines, both internal and external to inlet cowl, are presented. Transition duct aero-dynamics also plays an important role in design and understanding of aircraft inlets and is thus included in the treatment. Supersonic and hypersonic inlets with their attendant shock losses, boundary layer management, and instabilities such as buzz and starting problem are included in the inlet section of Chapter 5. The study of aircraft exhaust systems comprises the latter part of Chapter 5. Besides figures of merit, the performance of a convergent nozzle is compared with the de Laval or a convergent–divergent nozzle. The requirements of reverse-and vector thrust are studied in the context of thrust reversers and modern thrust vectoring nozzles. In the hypersonic limit, the exhaust nozzle is fully integrated with the vehicle and introductory design concepts and off-design issues are presented. Nozzle cooling is introduced for high-performance military aircraft engine exhaust systems and the attendant performance penalties and limitations are considered. Plug nozzle and its on-and off-design performances are introduced. Since mixers are an integral part of long-duct turbo fan engines, their effect on gross thrust enhancement is formulated and presented in the nozzle section in Chapter 5.

Chemical reaction is studied on a fundamental basis in Chapter 6. The principles of chemical equilibrium and kinetics are used to calculate the composition of the products of combustion in a chemical reaction. These principles allow the calculation of flame temperature and pollutant formations that drive the design of modern aircraft gas turbine combustors. Further details of flame speed, stability, and flame holding are presented in the context of combustion chamber and afterburner design. Pollutant formation and its harmful impact on ozone layer as well as the greenhouse gases in the exhaust are presented to give students an appreciation for the design issues in modern combustors. Aviation fuels and their properties and a brief discussion of combustion instability known as screech are included in Chapter 6.

Turbomachinery is introduced in three chapters. Chapter 7 deals with axial-flow com-pressors in two and three dimensions. The aerodynamics of axial-flow compressors and stage performance parameters are derived. The role of cascade data in two-dimensional design is presented. Emphasis throughout this chapter is in describing the physical phenomena that lead to losses in compressors. Shock losses and transonic fans are introduced. The physics of compressor instability in stall and surge is described. A simple model by Greitzer that teaches the value of characteristic timescales and their relation to compressor instability is outlined. Chapter 8 discusses the aerodynamics and performance of centrifugal compressors. Distinctive characters of centrifugal compressors are highlighted and compared with axial-flow compressors. Turbine aerodynamics and cooling are presented in Chapter 9. Component matching and engine parametric study is discussed in Chapter 10. Finally, chemical rocket and hypersonic propulsion is presented in Chapter 11.

Instructor Resources

The following resources are available to instructors who adopt this book for their course. Please visit the website at www.wiley.com/go/farokhi to request a password and access these resources.

• Solutions Manual
• Image Gallery

Acknowledgments

I express my sincere appreciation and gratitude to all those who have contributed to my understanding of fluid mechanics and propulsion. Notable among these are my professors in Illinois and MIT. Hermann Krier, Jack Kerrebrock, James McCune, William Hawthorne, and Ed Greitzer contributed the most. The fellow graduate students in the Gas Turbine Lab were also instrumental in my education. Choon Tan, Maher El-Masri, Alan Epstein, Arun Sehra, Mohammad Durali, Wai Cheng, Segun Adebayo, James Fabunmi, and Anthony Nebo discussed their dissertations with me and helped me understand my own. In the Gas Turbine Division of Brown, Boveri and Co. in Baden, Switzerland, I learned the value of hardware engineering and testing, advanced product development, and component research. My colleagues, Meinhard Schobeiri, Konrad Voegeler, Hans Jakob Graf, Peter Boenzli, and Horst Stoff, helped me understand how industry works and how it engineers new products. At the University of Kansas, my graduate students were my partners in research and we jointly advanced our understanding of fluid mechanics and propulsion. My doctoral students, Ray Taghavi, Gary Cheng, Charley Wu, Ron Barrett, and Kyle Wetzel, taught me the most. I appreciate the contributions of 30 M.S. students whom I chaired their theses to our ongoing research. The colleagues at NASA-Lewis (now Glenn) who sponsored my research and provided insightful discussions and hospitality over the summer months in Cleveland are Ed Rice, Khairul Zaman, Ganesh Raman, Bernie Anderson, Reda Mankbadi, James Scott, and Charlie Towne who welcomed me into their laboratory (and their homes), and we enjoyed some fruitful research together. The faculty and staff in the Aerospace Engineering Department of the University of Kansas have been very supportive for the past 23 years, and I would like to express my sincere appreciation to all of them. Vince Muirhead, Jan Roskam, Eddie Lan, Dave Downing, Howard Smith, Dave Ellis, Tae Lim, John Ogg, James Locke, Mark Ewing, Rick Hale, and Trevor Sorenson taught me an appreciation for their disciplines in aerospace engineering. I joined my colleagues in GE-Aircraft Engines in teaching propulsion system design and integration short courses to engineers in industry, FAA, and NASA for many years. I learned from Don Dusa and Jim Younghans from GE and Bill Schweikhard of KSR some intricate aspects of propulsion engineering and flight-testing.

I would like to thank the following colleagues who reviewed the draft manuscript:

David Benson, Kettering University

Kirby S. Chapman, Kansas State University

Mohamed Gad-el-Hak, Virginia Commonwealth University

Knox Millsaps, Naval Postgraduate School

Alex Moutsoglou, South Dakota State University

Norbert Mueller, Michigan State University

Meinhard T. Schobeiri, Texas A&M University

Ali R. Ahmadi, California State University and Polytechnic—Pomona

Ganesh Raman, Illinois Institute of Technology

Finally, I express my special appreciation to my wife of 36 years, Mariam, and our three lovely daughters, Kamelia, Parisa, and Farima (Fallon) who were the real inspiration behind this effort. I could not have contemplated such a huge project without their love, understanding, encouragement, and support. I owe it all to them.

Saeed Farokhi
Lawrence, Kansas
March 16, 2007