5-2 Gas Turbine Engines SQ

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  1. What is the purpose of the engine inlet?
    Acts as a diffuser and provides a turbulent-free supply of air to the face of the compressor
  2. Why should the inlet duct be constructed with a straight section?
    Smooth out turbulent airflow
  3. What are the advantages of a single-entrance duct?
    • Simplest
    • Most effective at providing smooth airflow
  4. What is the shape of a subsonic inlet duct? Why?
    • Divergent
    • Decrease velocity
    • Increase pressure
  5. What is the shape of a supersonic inlet duct? Why?
    • Convergent-Divergent
    • Convergent
    • Decrease velocity to subsonic levels
    • Increase pressure

    • Divergent
    • Decrease velocity of subsonic airflow
    • Increase pressure
  6. What is the purpose of a variable geometry inlet duct?
    • Allow supersonic aircraft to fly in all flight regimes (supersonic and subsonic)
    • Inlet shape will change depending on supersonic or subsonic airspeed
  7. What are the advantages and disadvantages of a centrifugal compressor? An axial flow compressor?
    • Centrifugal
    • Advantages
    • -Rugged
    • -Low cost
    • -Good power output over a wide range of RPMs
    • -High pressure increases per stage

    • Disadvantages
    • -Large frontal area required
    • -Impractical for multiple stages

    • Axial
    • Advantages
    • -High Peak efficiencies
    • -Small frontal area reduces drag
    • -Straight through-flow, allowing for high ram efficiency
    • -Combustion efficiency is better than centrifugal compressors (increased pressure rise by increasing the number of stages)
    • -With the dual/twin/split spool, starting flexibility is greater and it has improved high-altitude performance

    • Disadvantages
    • -At low inlet speed, airflow will decrease in the compressor, creating a high angle of attack on the rotor blades that could lead to a compressor stall (compressor stall discussed in later chapter).
    • -High-speed aircraft may experience an inlet air temperature of 250 degress F. because of ram effect. These high compressor inlet air temperatures cause low compression ratios (due to air density changes) and will also reduce the air supply to the rear compressor
    • -Good efficiencies only possible over a narrow rotational-speed
    • -Difficulty of manufacture and high cost
    • -High starting power requirements
  8. What are the parts of a centrifugal compressor and what is the function of each?
    • Impeller
    • increase velocity, pressure and total pressure

    • Diffuser
    • decrease velocity, increase pressure

    • Manifold
    • Route air mass to the burner
  9. What are the components of an axial flow compressor?
    • Rotors
    • Stators
  10. Why do rotor and stator vanes within an axial compressor decrease in length from the front to rear of the compressor?
    • The cross sectional area decreases within the compressor from for to aft to allow the velocity to remain fairly constant as pressure increases.
    • Therefore, the rotor and stator length requirements will decrease
  11. What do inlet and exit guide vanes do?
    Redirect airflow
  12. What is the function of the diffuser?
    Final decrease in velocity, Increase in pressure prior to combustion
  13. Describe a dual-spool axial flow compressor. Why is it used?
    Two separate compressors (low pressure and high pressure), driven by its own turbine, to obtain higher compressor ratios
  14. Where is fuel introduced within a gas turbine engine?
    In the burner
  15. What are the criteria for a good burner section?
    • Minimum Pressure Loss
    • High Combustion efficiency
    • Flame must not blow out
    • Contain the total combustion process
  16. What are the three types of combustion chambers? What are the advantages and disadvantages of each?
    • Can
    • Ease of maintenance
    • Cause cold spots on turbine

    • Annular
    • Even heat
    • Complicated maintenance

    • Can-Annular
    • Even heat
    • Ease of maintenance
    • Expensive
  17. What is primary and secondary air?
    • Primary
    • 25% mixes fuel for combustion

    • Secondary
    • 75% for cooling and flame control
  18. What is the purpose of the turbine section?
    To turn the compressors and accessories
  19. How much of the energy produced is used to turn the compressor and accessories?
    75% of the total heat energy produced prior to the turbine section
  20. What are the main parts of the turbine?
    • Stators
    • Rotors
  21. What is creep?
    Turbine blade elongation and deformation from being heated.
  22. What is the purpose of the exhaust duct?
    To increase velocity and decrease turbulence
  23. Describe a subsonic and supersonic exhaust duct and how each operates.
    • Subsonic
    • Convergent

    • Supersonic
    • Convergent/Divergent

    Both will maximize the increase in velocity at the expense of pressure
  24. Describe the four parts of an afterburner.
    • Spray bars
    • Flame holder
    • Screech liner
    • Variable exhaust nozzle
  25. Describe how an afterburner operates.
    Secondary air from burner section along with bypassed air (turbofan) is mixed with fuel and ignited in the afterburner duct to augment thrust.
  26. What controls the amount of thrust augmentation an afterburner will produce?
    The more fuel introduced, the more thrust produced
  27. What is the function of the spray bars? The flame holder?
    • Spray bars
    • Spray Fuel

    • Flame holders
    • Hold the flame and they create local turbulence (eddies) to enable a better fuel/air mixture for combustion
  28. What is a screech liner and how does it operate?
    It acts as a shock absorber to guard against pressure fluctuations or cyclic vibrations sometimes associated with afterburner
  29. What type of exhaust nozzle is used on an afterburner equipped aircraft?
    Variable exhaust nozzle
  30. How does subsonic airflow react through a convergent opening? A divergent opening?
    • Convergent
    • Velocity will increase
    • Pressure will decrease

    • Divergent
    • Velocity will decrease
    • Pressure will increase
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5-2 Gas Turbine Engines SQ
2016-06-16 14:46:01
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