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DESCRIBE inlet ducts
- Provides the proper amount of high pressure, turbulence-free air to the compressor
- Normally designed to act as a diffuser but never as a nozzle
- Straight and smooth as possible to reduce airflow distortion and friction.
- Can be single or divided entrance.
- Subsonic inlets are diffusers to increase airflow pressure and reduce velocity.
- Supersonic are Convergent-Diffuser to increase pressure and reduce velocity on the supersonic air to subsonic condition(convergent) and diffuser to continue the process.
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DESCRIBE compressors
- Used to supply enough air to satisfy the requirements of the combustion section.
- Increases the pressure and directs it to the burners.
- Three types:
- Centrifugal
- Has impeller, diffuser and manifold.
- impeller accelerates air to the diffuser and pressure is increased.
- Air then passes through the compress manifold and is directed to the combustion chamber.
- Axial-Flow
- Rotors and stator vanes form stages.
- Rotors increase the velocity and pressure of the incoming airflow to increase total pressure.
- Stator vanes act as diffusers to decrease velocity and increase pressure.
- You can have a dual axial with a low and high pressure compressors on different spool axials.
- Axial-Centrifugal Flow Compressor
- Design utilizes the combination of the axial and centrifugal flow compressor.
- Main advantage is the large pressure increase yet small size that makes it useful on helicopters and small aircraft.
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DESCRIBE the burner section of a gas turbine engine
- Contains the combustion chamber and provides for proper mixing of the fuel and air.
- Combust fuel/air mix to add thermodynamic energy for the turbine section/thrust
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DESCRIBE combustion chambers
- Types of combustion chamber:
- Can Combustion Chamber
- Each burner contains its own fuel nozzle, burner liner and casing.
- Primary air introduced at the nozzle supports combustionSecondary air provides cooling.
- Advantages are strength and durability, and ease of maintenance.
- Disadvantages are poor use of space, greater pressure loss, and uneven heat distribution, as well as possible damage due to one can failure.
- Annular Combustion Chamber
- Consists of a continuous, circular, inner and outer shroud around the outside of the compressor drive shaft.
- Fuel is introduced via nozzles where it is mixed and ignited with incoming air.
- Advantages are uniform heat distribution that aids in prevention of heat warping or turbine blade failure, as well as better mixing and better use of space.
- Disadvantage include hard to maintain, structural problems.
- Most often found on smaller engines, such as helicopters, where engine removal and tear down is not difficult.
- Can-Annular
- Used primarily on high performance engines.
- Consists of cans at the front where the fuel and air are mixed and burned.
- Hot gases then pass to the annular area of the chamber and mix together.
- Provides for easier maintenance, even temperature distribution, and greater structural stability.
- It is expensive.
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DESCRIBE the turbine section of a gas turbine engine
- Drives the compressor and the accessories.
- Converts heat energy (potential and kinetic) from the burner chamber into mechanical energy.
- Approx 75% of total pressure energy is converted. The remaining 25% is used for thrust.
- Most highly stressed part.
- Stator vanes come before the rotors. They prepare the airflow from the combustion chamber for the harnessing of power by the turbine rotor. They also deflect the gases at a specific angle in the direction of turbine wheel rotation.
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DESCRIBE the phenomenon of creep in a gas turbine engine
- The elongation of turbine blades due to excessive temperatures over long periods, resulting in permanent blade deformation.
- Deformed blades will not operate efficiently and may fail catastrophically.
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DESCRIBE the exhaust section of a gas turbine engine
- Directs the flow of hot gases rearward to cause a high exit velocity to the gases while preventing turbulence.
- Includes the exhaust outer duct, exhaust inner cone, and three or four radial hollow struts.
- Can use convergent nozzles for subsonic gas or convergent-divergent nozzles for supersonic.
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DESCRIBE the afterburner section of a gas turbine engine
- Method to increase maximum thrust available by 50% or more but at the cost of fuel consumption increased 300%.
- Secondary air from burner section is used on turbojets
- Secondary and bypass air on turbofans.
- 4 parts:
- Spray bars - introduce fuel to the afterburner
- Flame holders - provides a region in which airflow velocity is reduced and turbulent eddies are formed to allow proper mixing.
- Screech liner - control screech (violent pressure fluctuations caused by cyclic vibrations). Sleeves are corrugated and perforated to allow reduce pressure fluctuation and vibrations.
- Variable exhaust nozzle -
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