M15.4

Question 1

Primary function of the compressor?

Answer 1

Draws air from the inlet, increases its pressure, and delivers it to the combustion chamber.

Question 2

Secondary function of the compressor?

Answer 2

Supplies bleed air to aircraft systems.

Question 3

How is air compressed in gas turbine engines?

Answer 3

By accelerating airflow using aerodynamic principles (Bernoulli).

Question 4

Main components of a gas turbine compressor?

Answer 4

Rotor and stator.

Question 5

Function of the rotor in a compressor?

Answer 5

Accelerates the airflow.

Question 6

Function of the stator in a compressor?

Answer 6

Slows airflow and converts velocity into pressure.

Question 7

Purpose of Inlet Guide Vanes (IGVs)?

Answer 7

Guide airflow into the first stage and improve efficiency and stability.

Question 8

Two main types of gas turbine compressors?

Answer 8

Centrifugal flow and axial flow compressors.

Question 9

Main components of a centrifugal compressor?

Answer 9

Impeller, diffuser, and compressor manifold.

Question 10

Pressure rise per stage of a centrifugal compressor?

Answer 10

High, typically up to 8:1.

Question 11

Typical application of centrifugal compressors?

Answer 11

Turboprop and turboshaft engines.

Question 12

Advantage of centrifugal compressors?

Answer 12

High pressure rise per stage, simple, lightweight, low cost.

Question 13

Disadvantage of centrifugal compressors?

Answer 13

Large frontal area and turning losses.

Question 14

Main components of an axial compressor stage?

Answer 14

Rotor blades and stator vanes.

Question 15

Airflow direction in an axial compressor?

Answer 15

Parallel to the engine axis.

Question 16

Pressure rise per axial compressor stage?

Answer 16

Small, approximately 1.3:1.

Question 17

Why are many stages needed in axial compressors?

Answer 17

Each stage provides only a small pressure increase.

Question 18

Typical application of axial compressors?

Answer 18

Turbofan engines.

Question 19

What is a multi-spool compressor?

Answer 19

A compressor split into LP, IP, and/or HP rotors driven by separate turbines.

Question 20

Purpose of a fan in a turbofan engine?

Answer 20

Acts as a low-pressure compressor and produces bypass thrust.

Question 21

Why are fan blades carefully balanced?

Answer 21

To prevent vibration and bearing damage.

Question 22

What determines centrifugal force on a fan blade?

Answer 22

Blade mass, rotor speed, and distance from rotational axis.

Question 23

Define moment weight.

Answer 23

Blade mass multiplied by distance of its centre of gravity from the axis.

Question 24

Units used for moment weight?

Answer 24

Gram-inches, cm·g, or ounce-inches.

Question 25

Why is moment weight important?

Answer 25

It determines blade centrifugal force and balance.

Question 26

Preferred fan blade replacement method?

Answer 26

Single blade replacement with similar moment weight.

Question 27

What is normal airflow in an axial compressor?

Answer 27

Correct relationship between inlet air velocity and rotor speed.

Question 28

What causes compressor stall?

Answer 28

Excessive blade angle of attack causing airflow separation.

Question 29

Effects of compressor stall?

Answer 29

Turbulence, reduced airflow, possible local reversal.

Question 30

What is compressor surge?

Answer 30

A severe, unstable form of stall with airflow reversal.

Question 31

Why is aft-stage surge dangerous?

Answer 31

High pressure and short blades cause rapid, widespread effects.

Question 32

Mechanical causes of stall/surge?

Answer 32

Inlet icing, damaged blades, combustor or exhaust restrictions.

Question 33

Operational causes of stall/surge?

Answer 33

Incorrect engine speed or rapid throttle movement.

Question 34

Purpose of compressor bleed valves?

Answer 34

Vent excess air at low speeds to prevent stall.

Question 35

Benefit of multi-spool compressors?

Answer 35

Better airflow matching across stages.

Question 36

Purpose of variable stator/IGVs?

Answer 36

Maintain correct angle of attack at all engine speeds.

Question 37

Define compression ratio.

Answer 37

Ratio of largest to smallest volume in the combustion chamber.

Question 38

Why is axial velocity nearly constant through the compressor?

Answer 38

Increasing density offsets reducing flow area.

Question 39

Typical axial compressor stage pressure ratio?

Answer 39

Approximately 1.3:1.

Question 40

How do turbine engines achieve high overall pressure ratio?

Answer 40

Through multiple small pressure increases across many stages.