M15.4 Compressors

Question 1

What is the primary function of the compressor in a gas turbine engine?

Answer 1

To supply a sufficient quantity of air to satisfy the requirements of the combustion chamber.

Question 2

What are the two main components of a compressor?

Answer 2

• Compressor rotor
• Compressor stator

Question 3

What is the role of the rotor in a gas turbine compressor?

Answer 3

To suck in air and push it to the outlet side, increasing the energy of the airflow.

Question 4

What is the function of the stator in a gas turbine compressor?

Answer 4

To guide and slow the airflow to cause an increase in pressure.

Question 5

What is a compressor stage composed of?

Answer 5

A rotor and a stator.

Question 6

What are inlet guide vanes (IGVs)?

Answer 6

Fixed or movable stator vanes in front of a compressor stage that improve airflow into the first compressor stage.

Question 7

What are outlet guide vanes (OGVs)?

Answer 7

Stator vanes in the fan duct that improve airflow into the fan nozzle.

Question 8

What are the two types of compressors used in gas turbine engines?

Answer 8

• Centrifugal flow compressor
• Axial flow compressor

Question 9

What is a characteristic of centrifugal-flow compressors?

Answer 9

They have a high-pressure rise per stage, around 8:1.

Question 10

What are the main components of a centrifugal flow compressor?

Answer 10

• Impeller (rotor)
• Diffuser (stator)
• Compressor manifold

Question 11

What is the typical limitation of centrifugal compressors?

Answer 11

Limited to two stages due to efficiency concerns.

Question 12

What is the main function of the impeller in a centrifugal compressor?

Answer 12

To pick up and accelerate the air outwardly to the diffuser.

Question 13

What is the advantage of axial flow compressors in terms of airflow?

Answer 13

They compress air while maintaining the original direction of flow, avoiding energy loss.

Question 14

Where are axial flow compressors typically found?

Answer 14

On turbofan engines widely used in aviation.

Question 15

What is the structure of an axial flow compressor?

Answer 15

It consists of rotating components with aerofoil-shaped blades and stationary vanes mounted to the casing.

Question 16

What is a single-spool compressor?

Answer 16

A compressor with a single drum and multiple stators.

Question 17

What is a multi-spool compressor?

Answer 17

A compressor consisting of two or three drums of rotors, each driven by a separate turbine segment.

Question 18

What are the advantages of centrifugal flow compressors?

Answer 18

• High pressure rise per stage
• Efficiency over a wide rotational speed range
• Simplicity of manufacture and low cost
• Low weight
• Low starting power requirements

Question 19

What are the disadvantages of centrifugal flow compressors?

Answer 19

• Large frontal area for a given airflow
• Losses in turns between stages

Question 20

What are the advantages of axial flow compressors?

Answer 20

• High peak efficiencies
• Small frontal area for given airflow
• Straight through flow allowing high ram efficiency
• Increased pressure rise with negligible losses

Question 21

What are the disadvantages of axial flow compressors?

Answer 21

• Good efficiencies only over a narrow rotational speed range
• Difficulty of manufacture and high cost
• Relatively high weight
• High starting power requirements

Question 22

What causes compressor stall?

Answer 22

Changes in the angle of attack due to rotor speed or inlet velocity changes.

Question 23

What is compressor surge?

Answer 23

A severe form of compressor stall characterized by rapid airflow decrease and blockage.

Question 24

What are two operational reasons for compressor stall and surge?

Answer 24

• Engine speed too far below design speed
• Incorrect acceleration or deceleration

Question 25

What is one method to prevent compressor stall and surge?

Answer 25

Use of compressor bleed valves.

Question 26

What is the moment weight of a fan blade?

Answer 26

The product of the blade mass and the distance of the center of gravity from the rotational axis.

Question 27

What happens if the moment weight of a fan blade changes due to blending?

Answer 27

The original weight is crossed out and the new moment weight is marked on the root.

Question 28

How are fan blades matched on a fan disc?

Answer 28

Using computerized balancing to determine the best position for each blade.

Question 29

What is the best method to change a single fan blade?

Answer 29

Replace it with a new blade that has a moment weight as close as possible to the old one.

Question 30

What can cause airflow separation in a compressor?

Answer 30

Increased angle of attack on rotor blades and stator vanes.

Question 31

What are the three design methods to prevent compressor stall and surge?

Answer 31

* Use of compressor bleed valves * Use of dual or triple-spool rotors * Use of variable compressor stator vanes

Question 32

What can cause a blockage to the airflow in an aircraft engine?

Answer 32

Compressor stall and surge

Question 33

What are the two operational reasons for compressor stall?

Answer 33

* Speed of the engine too far below design speed * Incorrect acceleration or deceleration

Question 34

Name one method to avoid compressor stall and surge.

Answer 34

Compressor bleed valves

Question 35

What is another method used to prevent compressor stall and surge apart from bleed valves?

Answer 35

Dual or triple-spool rotors

Question 36

What is the most modern method to prevent compressor stall?

Answer 36

Variable compressor stator vanes

Question 37

How do compressor bleed valves function?

Answer 37

They are open at low engine speeds to allow excessive airflow to escape overboard

Question 38

Where are bleed valves typically located in an aircraft engine?

Answer 38

In the mid-section and sometimes in the aft section of the engine compressor

Question 39

What are the two parts of a dual spool engine called?

Answer 39

* Low-pressure compressor (N1 compressor) * High-pressure compressor (N2 compressor)

Question 40

What is the advantage of variable stator vanes?

Answer 40

They allow for an optimum angle of attack on the following rotor blades for every engine speed

Question 41

What is a disadvantage of variable stator vanes?

Answer 41

They require a very complicated control mechanism

Question 42

What does the compression ratio of an internal combustion engine represent?

Answer 42

The ratio of the volume of its combustion chamber from its largest to its smallest capacity

Question 43

What is the pressure ratio per stage in an axial flow compressor?

Answer 43

About 1.3:1

Question 44

If the air pressure entering the first stage of an axial flow compressor is 10 psi, what will the output pressure be after the first stage?

Answer 44

13 psi

Question 45

How do you calculate the output pressure of subsequent stages in a compressor?

Answer 45

Multiply the input pressure by the pressure ratio of 1.3

Question 46

True or False: The axial velocity of gas in a compressor remains constant from the front to the rear.

Answer 46

True

Question 47

Fill in the blank: The pressure increase at each stage of a compressor is very _______.

Answer 47

small

Question 48

What is necessary to raise the pressure to high values for efficient combustion in a compressor?

Answer 48

Many stages