Best high speed and high altitude performance. Highest TSFC. Longest takeoff rolls.
How is a turbofan constructed?
Fan, compressor, burner, turbine, exhaust nozzle.
How does a turbofan produce thrust?
Fan pushes a large mass of air and provides 30-60% of the total thrust.
How much thrust is produced by the fan on a turbofan?
30-60% from the fan.
40-70% from the gas generator exhaust gases.
What is meant by "bypass air?"
Airflow from the fan "bypassed around the gas generator."
What are the +- of the turbofan?
Better TSFC than a turbojet
shorter takeoff distance
can lift larger weights
Large frontal area, slower, and can not fly as high as turbojet.
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 and most effective at providing smooth airflow.
4. What is the shape of a subsonic inlet duct? Why?
Divergent. Decrease V increase P
5. What is the shape of a supersonic inlet duct? Why?
>< (c/d) decrease V increase P
6. What is the purpose of a variable geometry inlet duct?
To allow a supersonic aircraft to fly in all flight regimes (ss and subsonic)
7. What are the advantages and disadvantages of a centrifugal compressor? Of an axial flow compressor?
+: Rugged, low cost, good power output over wide range of RPMs, High pressure increases per stage
-: Large frontal area required, impractical for multiple stages
+ High peak efficiencies, small frontal area reduces drag, straight through flow allowing for high ram eff, combustion efff is better than centrifugal, with dual/twin/split starting flex is greater, improved high alt performance.
- Low inlet speed=>compressor stall, narrow rotational speed for good eff, high cost, difficult to manufacture, high starting power requirements.
8. What are the parts of a centrifugal compressor and what is the function of each?
Impeller: +V, P, Pt
Manifold: route air mass to burner
9. What are the components of an axial flow compressor?
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 fore 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 the flow
12. What is the function of the diffuser?
13. Describe a dual-spool axial flow compressor. Why is it used?
Two separate compressors, 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 is 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 engine.
Annular- even heat, complicated maintenance.
Can-Annular- even heat, ease of maintenance, expensive
17. What is primary and secondary air?
Primary air = 25% mixes fuel for combustion
Secondary air=75% cooling and flame control
18. What is the purpose of the turbine section?
To turn the compressor 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 and rotors
21. What is creep?
Turbine blade elongation and deformation
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 c/d ><
Both will maximize the increase in velocity at the expense of pressure.