Turbofan Flashcards
Combustion chamber design requirements
high efficiency wide stability range reliable ignition restart at altitude durable
Basic constraints of combustion chamber
burning velocity 10ms^-1
typical range of air/fuel ratios 35-150
range of burning air/fuel ratios 7-22
Annular combustion chamber(+/-)
Positive shorter length for given power output more compact less material less cooling flow required
Negative
structurally weak
complex to manufacture
difficult to control exit temperature
Turbine - operating conditions
gas velocity from combustions 457ms^-1 gas flow temperature 1600 degrees each blade produces 560kW rotates at approx 10,000rpm each blade exerts an outward force of approx 18 tonnes required to operate for 20,000 hours single-crystal blades
Function of compressors
to raise the temperature and pressure of the incoming air
the turning motion of the rotor blades accelerates the air
the stator blades redirect the airflow on to the next stage of rotor blades making sure it approaches them at the correct angle
How is the velocity of the incoming air into the combustion chamber reduced?
recirculating air regions are used to reduce the velocity of the incoming air
Turbine blade internal air cooling
each blade has channels that direct airflow through the perforations on the surface cooling the blade to below the material’s melting point
Non contact seals in compressors
they allow rotor blades to move with respect to the NGVs without letting escape between any gaps
Materials used
titanium
steel
nickel-based alloys
Titanium
lower mass
less energy required to spin the fan and compressors
Steel
used in rotating assemblies
hard-wearing
high melting points
Nickel-based alloys
high melting points
require cooling
Single crystal
whole structure only contains one crystal
achieved using a bridgemass furnace
rate of cooling controlled
