Compressors

Question 1

What is the primary purpose of a compressor?

Answer 1

to increase pressure by guiding the flow of air through a series of carefully shaped channels

Question 2

How are the channels in a compressor obtained?

Answer 2

as a consequence of the arrangement of the stationary stator and rotary rotor

Question 3

Does the compressor do work on the fluid?

Answer 3

no, so it requires a power supply

Question 4

Where is the work exchanged between?

Answer 4

the fluid and machine only in the rotor

Question 5

What is one pair rotor/stator called?

Answer 5

a stage

Question 6

What is happening to the pressure inside the compressor channels?

Answer 6

pressure is increasing to avoid flow separation

Question 7

What does absolute velocity do?

Answer 7

increases across the rotor and diminishes across the stator, pressure increases

Question 8

What does relative velocity do?

Answer 8

decreases across the rotor, pressure increases

Question 9

What are axial compressors?

Answer 9

machines where air enters and leaves in a direction parallel to the axis of rotation

Question 10

What can be said about the pressure increase in the compressor?

Answer 10

it is gradual

Question 11

What is the pressure rise typically between?

Answer 11

1.1 and 1.6

Question 12

What is necessary to maintain constant axial velocity?

Answer 12

a gradual decrease in the area between the rotor shaft and the stator casing

Question 13

What does the last row of stators do in a compressor?

Answer 13

they ensure that any residual swirl within the flow is removed before the flow passes into the combustion chamber

Question 14

What do centrifugal compressors do?

Answer 14

they realise a pressure increase by means of a combination of channel shape and centrifugal effect which establishes a radial flow

Question 15

What are some benefits of the centrifugal compressor?

Answer 15

more robust than the axial type
easier to develop and manufacture

Question 16

What happens in a centrifugal compressor?

Answer 16

> the impeller rotates at high speeds and is continually induced into the centre of the impeller
centrifugal action causes it to flow radially outwards along the vanes on the surface of the impeller disc
this accelerates the air causing a slight increase in pressure
air leaving the impeller passes into the diffuser section where the vanes from divergent passages

Question 17

What can be said about each single stage of the centrifugal compressor?

Answer 17

each stage has a higher compression ratio than a single axial stage
r between 4-6

Question 18

What should the combustion chamber be capable of?

Answer 18

*complete combustion of large quantities of fuel
*small volume and minimum pressure loss
*deliver uniform temperature
*exit temperature low enough for turbine blades
*expected life of the order is 10,000 hours
*produce low nitrous oxide and hydrocarbon emissions
*operate over the whole range if engine speed, flight speed and altitude

Question 19

What does the typical configuration of a combustion chamber include?

Answer 19

*injection zone
*ignition zone
*primary combustion zone
*seconday combustion zone
*tertiary combustion zone