Gas Turbine Compressor

Answer 1

Highe compression ration&raquo_space;more thermal efficient

35:1

Question 2

Compression ratio

Answer 2

Is the ratio of compressor output to compressor inlet pressure

Question 3

Types of compressor

Answer 3

~axial flow compressor

~centrifugal compressor

Question 4

Centrifigual compressor compression ratio

Answer 4

With one centrifugal&raquo_space;4,5:1
2 stages&raquo_space; theoretically 20.25 :1 But in reality 12:1

Cannot aerodynamically stall

Is too noisy and is not enough as new axial compressors

Question 5

Axial flow compressor

Answer 5

Rotors are always before the stator and the stator makes a divergence angle to slow down the speed and increase the static pressure and temperature
Compression ratio&raquo_space; 1,1 :1 to 1,2:1 (10% to 20%)

~across rotor velocity,pressure and temp increases
~across the stator the velocity reduces and pressure ,temperature increase

Across the multiple stages velocity remains constant,but pressure and temperature increases

Answer 6

Convergent air annulas from the front part to the rear part in the compression stage

Question 7

Compressor stall

Answer 7

Blade stall:
~damage
~ice
~extreme incidence angles

Symptoms of compressor stall are:
~high gas temperature
~reduce thrust
~rumbling or banging from the compressor
~fluctuating RPM and fuel flow

Question 8

Compressor surge

Answer 8

~a very severe stall compressor output pressure falls below combustion pressure,gases flow forward through the compressor
~in an extreme case flames may be seen exiting intake
~over fuelling can cause a surge by creating excessive pressure in the combustor (mostly eliminated my electronic modern fuel control units)

Question 9

Stall alleviation

Answer 9

~variable inlet guide vanes (VIGV) adjust their angle to ensure that air directed onto the first stage .
~on some engines variable stator vanes (VSVs) do the same thing for each stage

Answer 10

Handling bleed or inter stage bleed or transient bleed

To expel air if in excess

Question 11

Stall alleviation - bleed valves

Answer 11

~inter stage valves vent pressure during the start to improve axial flow across the compressor (know as handling bleed).
These reduces the load on the compressor bringng it closer to the working line during engine start.

Generally ,valves are open when eng switched off and gradually close,to become fully closed at ground idle speed

Answer 12

MULITPLE SPOOL
~allow each compressor to run at its optimal speed
~reduce the need for complex air control system to prevent stall and surge

Question 13

Compressor blades

Answer 13

Rotor blades are fitted loosely so that they take up a least stress position during rotation

Blades are held in three ways :
~mechanically&raquo_space;the dovetail
~centrifugally»
~aerodynamically»air pressure will hold the blade in a stable positon

Question 14

centrifugal compressor benefits

Answer 14

~is cheaper,less prone to surge and damage,shorter and reasonably efficient

But has low compression ration 4,4:1 compraed to at least 35:1` for anaxial flow
~for given mass flow it requires a larger frontal area
~it less efficient than axial comprewssor

Question 15

Axial

Answer 15

~is very efficent
~has high compression ratio
~ is vuknerable to surge

Answer 16

~the compressor will delivery high pressure (compressed) air into the mid -frame diffuser (p3)
~the diffuser causes a slight reduction in air velocity ready for the combustor
~air from this point as tapped to produce HP bleed air
~the diffuser also allows a separation of airflow into dilution (80%) (secondary air)and combustion air (20%)(primary air).

Answer 17

Main funtion of internal air bleed
~internal engine and seconary cooling
~bearing chamber sealing
~prevention of hot gas ingestion into turbine disc cavaties
~engine anti icing

bleed air is taklen from an appropraite compressor stage depending on the required task:
~HP air is used to cool the turbine nozzle guide vanes ,the turbine blades and the turbine discs
~LP air used to cool the accessories
~air of differing pressures and temperature is used to seal the bearing chambers

Engine anticing uses HP air like the spinner