Special Problems Aerospace Manufacturing

1. Basic Principles of Gas Turbine Engines

Serafettin ENGIN, Ph.D.

ECOLE POLYTECHNIQUE MONTREALENGINEERING FACULTY

DEPARTMENT OF MECHANICAL ENGINEERING

Montreal, Quebec

AER8505Problmes Spciaux de Fabrication Aronautique

Special Problems in Aerospace Manufacturing

Serafettin Engin AER8505

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The fundamental idea; Forcing a stream of vapor, liquid, or any other substance through a narrow

aperture will produce a force acting in the opposite direction, in accordance with Newtons

basic lows.

In gas turbine engines, this principle is applied by installing a compressor towards front of the

engine, to draw in a large volume of air and hold it at high pressure.

A set of burners are then positioned in the gas flow behind the compressor, injecting fuel into the

gas stream and igniting it.

With fuel supplied and burners active, the temperature and volume of the following gas increase

greatly, but with the compressor blocking forward flow, the net result is to expel the gas

rapidly in the opposite direction, back towards the exit at the high velocity, thus generating

forward thrust.

A turbine situated in the path of escaping gas provides the power for the compressor, so the cycle

can continue as long as fuel continues to be supplied to the burners.


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A simple gas turbine

engine consists of five

distinct sections: inlet

duct, compressor,

combustion chamber,

turbine and exhaust

duct.

Sandvik


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A simple gas turbine engine consists of five distinct sections: inlet

duct, compressor, combustion chamber, turbine and exhaust duct.

Sandvik


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2. Aircraft/Aerospace Engines2.1. TurbojetsTurbojets generate their thrust from a relatively small mass of highly accelerated

air, all of which passes through the body of the engine. Only the minimum power

for operating the compressor and any other components is removed, with the

rest being used entirely for propulsion. Turbojets produce low trust at low

takeoff speeds, so aircraft powered by turbojets need long takeoff rolls.

However, turbojets have the lightest specific weigth and smallest frontal area,

which offers design advantages. They are well-suited for high speed, high

altitude long distance flights.


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2. Aircraft/Aerospace Engines2.2. TurbofansTurbofans are similar, but have a duct-enclosed fan at the front of the engine, to

help in producing additional thrust without requiring an increased fuel flow.

Instead, more of the fuel energy is converted into pressurized gas energy,

allowing turbofans to generate more thrust than simple turbojets and require

shorter take off runs. This increased efficiency is combined with a substantial

noise reduction, typically 1020%, a very important consideration. Turbofans

suit long range, high speed flights.


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2. Aircraft/Aerospace Engines2.3. TurbopropsTurboprops are easily recognized by their propellor blades positioned at the front of the engine. In this design, the majority of the gas stream energy is used to drive the propeller blades, along with powering the compressor. Turboprops are highly efficient at low airspeeds, resulting in short take off rolls. But the design is more complicated and heavier than turbojets or turbofans, and the physical presence of the blades and the jets larger frontal area requires design alterations to the aircrafts undercarriage for support. Turbofans are limited to airspeeds of approximately 500 mph/800 km/h, and are best for flying heavy loads off short or medium runways.

Turboshafts, the engines used to drive helicopter rotor blades, are essentially similar to turboprops.


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3. Engine Components

Engine Components (Sandvik)


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3. Example Engine Parts and Manufacturing Processes

Combustion chamber,Liners (Nickel alloys):forming, welding, laser drilling, turning,milling

Shafts:deep hole drilling,turning, milling, grinding

Fuel Nozzles:milling, turning, drilling, brazing

Rotors; Fans, compressors, impellers (Ti):turning, flank milling, point milling, drilling

Light alloy cases (Al, Mg):casting, high speed machining, drilling, boring

Turbine Discs (Nickel Alloys):Turning, milling, broaching, drilling, grinding


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References: A. F. El-Sayed, "Aircraft propulsion and gas turbine engines", 2008 Sandvik, Aerospace Engines and Gas Turbines Application Guide, 2002 B. Gunston, "The development of jet and turbine aero engines", 2006 S. Farokhi, "Aircraft propulsion", 2009 M.J.L. Turner, "Rocket and spacecraft propulsion : principles, practice and new developments", 2009 F.C. Campbell, "Manufacturing technology for aerospace structural materials", 2006 Y. ALTINTAS, Manufacturing Automation, Cambridge University Press, 2000 G. TLUSTY, Manufacturing Processes and Equipment, Prentice Hall, 2000 D. STEPHONSON and J. AGOPIOU, Metal Cutting Theory and Practice, Marcel Dekker Inc., 1997 Dyadem Press , "Guidelines for failure mode and effects analysis for automotive, aerospace and general manufacturing industries", 2004 G. Taguchi, S. Chowdhury, S. Taguchi, "Robust engineering", 2000 M. Jahazi, M. Elboujdani, P. Patnaik, "Aerospace materials and manufacturing : emerging materials, processes, and repair tech.", 2006 G. BOOTHROYD and W. A. KNIGHT, Fundamentals of Machining and Machine Tools, Marcel Dekker Inc., 1989 E. TERNT and P. K. WRIGHT, Metal Cutting, Fourth Edition, Butterworth-Heinemann, 2000 K. KARINO, Trouble Shooting For Cutting, Mitsubishi Materials, 1998 ASM, ASM Handbook, Volume 16 Machining, ASM International, 1997 M.O.M. OSMAN, Metal Cutting and Surface Technology, Concordia University E.J.A. ARMAREGO and R.H. BROWN, The Machining of Metal, Prentice Hall Inc., 1969 M. KRONENBERG, Machining Science and Application, Pergamon Pres, 1966 T.H.C. CHILDS, K. MAEKAWA, T. OBIKAWA and Y. YAMANE, Metal Machining Theory and Practice, John Wiley & Sons Inc., 2000 N.N. ZOREV, Metal Cutting Mechanics, Pergamon Press, 1966 N.H. COOK, Manufacturing Analysis, Addison-Wesley Publications Inc., 1966 G. BOOTHROYD, Fundamentals of Metal Machining, Edward Arnold Publishing Ltd., 1965 M.C. SHAW, Metal Cutting Principles, The Technology Press, M.I.T. Cambridge, 1984 F.F. LING, Surface Mechanics The American Society of Mechanical Engineers ASME Journal of Manufacturing Science & Engineering International Journal of Machine Tools and Manufacture, Annals of the CIRP

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Special Problems Aerospace Manufacturing