Tuesday, February 9, 2010

Gas Turbine Engines

Gas turbine engines are widely used in different fields for generate energy. They are commonly used in aircrafts. If you watch a huge passenger aircraft, you can see the gas turbine engines are either hanging on the wing section or tail section. Those power plants gives enough energy to generate thrust which finally result the aircraft fly.

Figure: An Airbus A340's 4 engines are situated on the wing, 2 in each side.

Figure: A Tupolev 154 Aircraft where engines situated on the empennage 
How does a gas turbine engine work?
There are several sections inside of an engine. First one is the air intake and fan which direct the air to inside of the engine, then the compressor, which compress the air to a very high pressure while reducing its speed. Then air meets the combustion chamber, where kerosene (fuel) is spread as small particles and burned in a high temperature.  Then this high speed, energized hot gas meets the turbine. Turbine rotates, using the kinetic energy from high speed gas.
  The most interesting thing is that the turbine is connected with the compressor via a valve. This means, the turbine makes the compressor rotate, obviously with a very high angular velocity.  This combination process results the thrust.

Figure: Simple Schematic view of a gas turbine engine
…->Rotation of the compressor-> compressed air-> combustion-> combusted air with high energy->Rotation of the turbine-> once again rotation of the compressor->…
Compressor and turbine consists of blades which has different functions which are called stators and rotors. They are usually fixed in to disks. Blades are situated in different stages which have different forms and sizes.

Figure: Variation of blade sizes
Figure: Opened engine, turbine blades
 A blade as a single element reminds a small scaled aircraft wing.  What I wanted to say, is that every blade has an aerodynamically designed profile.
Figure: Blades

Additionally the combustion chamber is one of the most important elements of a gas turbine engine.
Figure : A combustion chamber of a Gas turbine engine
 These elements can be destroyed or deteriorated by stone/ sand which engine may sucks during the departure or landing. Change of the aero dynamical shape of a blade can result fuel inefficiency and even a future failure of the engine during the flight.  So it is utmost important to inspect them frequently. Although opening up an engine is not profitable. That waste time and money. That is when NDT engineers use a borescope to inspect inside of an engine.