P Gas Turbine Compressor Flashcards
What are the 2 types of compressor?
- Axial flow
- Centrifugal
How can a centrifugal compressor stall?
Centrifugal compressors cannot stall
What’s the max compression ratio of a centrifugal compressor?
4.5:1
What is an axial flow compressor made up of?
Series of rotor blades accelerate the air towards stationary stator blades
What does a compressor rotor do to P, V and T?
P - increases
V - increases
T - increases
What does a compressor stator do to P, V and T?
P - static pressure increases
V - reduces
T - constant
What is the name for when one stage stalls, causing others to stall?
Surge
What is the name for complete reversal of airflow through the compressor?
Deep surge
What can trigger blade stall?
- Damage
- Ice
- Extreme angles of incidence
What is the consequence of compressor stall?
Reduced thrust
What are the 4 symptoms of compressor stall?
- High gas temperature (EGT)
- Reduced thrust
- Rumbling or banging from the compressor
- Fluctuating RPM and fuel flow
What can over fueling cause?
Surge, by creating excessive pressure in the combustor
Mostly eliminated by modern FCU’s
What are variable inlet guide vanes (VIGV)?
Vanes in the inlet which adjust their angle to ensure air is directed onto the 1st stage at the correct angle
What are variable stator vanes?
Ensure the optimum angle of attack for each rotor for each stage
What is the purpose of inter stage bleed valves?
Vent pressure during start to improve axial flow across the compressor, reduces load on the compressor
Why are rotor blades fitted loosely?
So that they take up a position of least stress
What is the compression ration of an axial flow compressor?
35:1
Where is bleed air taken from?
Jut before the combustor after the compressors
What does the diffuser do?
Allows a separation of airflow into dilution air (80%) and combustion air (20%)
What are the side effects of taking bleed air from the engine?
Reduced power thrust
Increases specific fuel consumption
What are the main functions of the internal bleed air system?
- Internal engine and accessory cooling
- Bearing chamber sealing
- Prevention of hot gas ingestion into turbine disc cavities
- Engine anti icing
