15.4 Compressors

Question 1

What are the two main components of a compressor?

Answer 1

-stator
-rotor

Question 2

What are the two main types of compressor?

Answer 2

-centrifugal flow
-axial flow

Question 3

What is an inlet guide vane and outlet guide vane?

Answer 3

Inlet - first row of stator vanes
Outlet - stator vanes in the fan duct for bypass

Question 4

How many stages can a centrifugal compressor have ?

Answer 4

2

Question 5

How many stages can a centrifugal compressor have ?

Answer 5

2

Question 6

What is the rise per stage on a centrifugal compressor?

Answer 6

8:1

Question 7

What are the two main functional elements of a centrifugal compressor?

Answer 7

Impeller
Diffuser

Question 8

What is the function of the impeller?

Answer 8

Accelerating air outwardly to the diffuser

Question 9

What are the two types of impeller available?

Answer 9

Single or double entry

Question 10

Where are centrifugal compressors typically used?

Answer 10

Turbo prop
Turbo shaft

Question 11

What are the shapes of axial compressor blades?

Answer 11

Aerofoil

Question 12

What does the gradual decrease in diameter allow for in an axial flow compressor?

Answer 12

Steady axial velocity as pressure and density increase

Question 13

What does a multi spool compressor allow for?

Answer 13

Maximum possible compression ratio

Question 14

What does the fan become in a three spool engine?

Answer 14

A low pressure compressor

Question 15

What is another role of stator in a compressor?

Answer 15

Direct airflow straight

Question 16

What ratio will a stage on an axial compressor achieve?

Answer 16

1:1-1:2

Question 17

What are the advantages of an axial compressor?

Answer 17

-negligible losses over stages increasing pressure
-higher RAM air efficiency

Question 18

What is the purpose of moment weighing?

Answer 18

Blade mass and distance of centre of gravity must be measured to account for manufacturing defects

Question 19

What is recorded on blade root?

Answer 19

Moment weight
Serial number
Part number

Question 20

What is the purpose of computerised fan blade distribution?

Answer 20

Using a computer to show where the optimum blade layout is

Question 21

Where not possible to get a fan blade of close enough weight what must be done?

Answer 21

Swap in pairs and use balance screws

Question 22

What is the relationship between rotor speed and angle of attack?

Answer 22

The higher the rotor speed means the larger the angle of attack

Question 23

What is the relationship between airspeed and angle of attack?

Answer 23

Higher airspeed means smaller angle of attack

Question 24

Why is a low angle of attack ideal?

Answer 24

It allows smooth airflow

Question 25

What causes compressor stall?

Answer 25

High angle of attack causes airflow separation in the rotor and vortices form causing slow, stopped or reversed flow

Question 26

What is compressor surge?

Answer 26

-rapid decrease in airflow
-stall causes a blockage causing subsequent stalls
-low pressure zones reverse airflow

Question 27

What can cause stall and surge?

Answer 27

-damaged or dirty blades
-damaged or dirty inlet
-damaged or broken compressor

To low idle speed
Acceleration or deceleration incorrectly

Question 28

How do bleed valves avoid stall?

Answer 28

-Mid and aft compressor locations
-Excessive air from forward stages can escape
-Open at low engine speeds

Question 29

How do variable stator/ variable inlet guide vanes prevent stall?

Answer 29

They are the most effective
They move along vertical axis
Optimum angle of attack can be achieved

Question 30

What is the axial flow compression per stage?

Answer 30

1.3:1