15.4 COMPRESSORS👌🏼

Question 1

What are the 2 components of a compressor

Answer 1

• rotor
• stator

Question 2

What do stator vanes do

Answer 2

• guide and slow airflow to cause pressure increase

Question 3

Combination of a rotor and stator is named what

Answer 3

• compressor stage

Question 4

Are rotors or stators first in a compressor

Answer 4

Rotors

Question 5

What are the set of stator vanes in front of a compressor stage named

Answer 5

Inlet guide vanes

Question 6

Explain inlet guide vanes

Answer 6

Straighten airflow into first compressor stage

Question 7

What are the 2 types of compressors

Answer 7

• centrifugal flow compressor
• axial flow compressor

Question 8

What do the rotors do

Answer 8

Increase energy of airflow

Question 9

How many stages do centrifugal compressors have and why

Answer 9

• 2
• They have a high pressure rise per stage

Question 10

Explain the double entry type impeller

Answer 10

• smaller diameter but operated at higher rotational speed to assure sufficient airflow

Question 11

What compressors are usually found on turbofan engines

Answer 11

Axial

Question 12

What compressors are commonly used in turboprop and turboshaft engines

Answer 12

• centrifugal compressors

Question 13

Explain axial compressors

Answer 13

• stators and rotors
• rotating components are aero foil shaped
• multiple stages (small increase per stage)

Question 14

Why is there a gradual decrease in diameter of the rotating drum and casing

Answer 14

• As it moves from low to high pressure
• necessary to maintain steady axial velocity, as pressure and density of air increase

Question 15

In triple-spool engines what is the fan referred to as

Answer 15

LP compressor

Question 16

Centrifugal compressors advantages

Answer 16

• HP rise per stage
• efficiency over wide rotational speed range
• simple
• low weight
• low starting power requirements

Question 17

Centrifugal compressors disadvantages

Answer 17

• large frontal area
• losses in turns between stages

Question 18

Axial flow compressor advantages

Answer 18

• small frontal area
• straight through flow
• increasing pressure rise by increasing stages

Question 19

Axial flow compressor disadvantages

Answer 19

• difficult to manufacture, expensive
• heavy
• high starting power requirements

Question 20

3 parameters that create centrifugal force on a engine

Answer 20

• rotor speed
• blade mass
• distance of CG of fan blade from rotational axis

Question 21

Explain moment weight

Answer 21

• distance of CG from rotational axis

Question 22

Where is the moment weight usually seen on the blade

Answer 22

Blade root

Question 23

What information is on the blade root

Answer 23

• part number
• serial number
• moment weight

Question 24

How are the blades moment weight calculated

Answer 24

By computerised balancing

Question 25

How can fan blade no1 be identified

Answer 25

• index mark on fan disc
• offset hole

Question 26

How are the blades numbered

Answer 26

• often numbered in the direction of rotation

Question 27

What is the best method to replace a fan blade

Answer 27

• replace with a new blade that has a moment weight as close as possible

Question 28

Explain balance weights

Answer 28

• use to balance the difference in the moment weight

Question 29

Where are the balance weights installed

Answer 29

• fan disc
• spinner cone

Question 30

What are the 2 methods of a fan blade change

Answer 30

• replace single blade with one that has similar moment weight
• replace a pair of blades with similar moment weights

Question 31

What must be ensured to allow smooth airflow into the rotor

Answer 31

• AOA to the rotor blades is small
• Blade is aerofoil shaped

Question 32

Explain stator vanes

Answer 32

• decelerate airflow and guide it to the next rotor stage of compressor

Question 33

When will the AOA increase on the rotor

Answer 33

• when inlet air velocity decreases

Question 34

Airflow separates from the compressor aerofoils and causes turbulent airflow is known as what

Answer 34

Compressor stall

Question 35

Explain compressor stall

Answer 35

• airflow slows down, stop or even reverse direction

Question 36

Explain compressor surge

Answer 36

Severe form of compressor stall

Question 37

Explain surge in the forward stages

Answer 37

• affects a part of the compressor blades
• due to bigger blade dimensions
• not very dangerous

Question 38

Explain surge in the aft stages

Answer 38

• develops rapidly over a large part of the compressor
• due to high pressure in aft stages and the short compressor blades

Question 39

What are the 2 operational reasons for compressor stall and surge

Answer 39

• engine speed below design speed
• stall at incorrect acceleration or deceleration

Question 40

3 methods to avoid compressor stall and surge

Answer 40

• compressor bleed valves
• use dual or triple spool rotors instead of single spool rotors
• use variable compressor stator vanes

Question 41

What is the modern method to avoid stall and surge

Answer 41

• variable compressor stator vanes

Question 42

Explain bleed valves

Answer 42

• found in mid-section/aft-section of engine compressor
• open at low engine speeds

Question 43

What is the N1 compressor known as

Answer 43

Low pressure compressor

Question 44

What is N2 compressor known as

Answer 44

• high pressure compressor

Question 45

Explain variable inlet guide vanes/variable stator vanes

Answer 45

• most effective to prevent stall
• moveable along vertical axis
• found in FWD stages of HP compressor

Question 46

Each stage of an axial flow compressor has a pressure ratio of?

Answer 46

1.3:1

Question 47

What compensates for the lost thrust as aircraft speed increases

Answer 47

Ram recovery (total pressure recovery)