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CAA Module 15 > Module 15.4 Compressors > Flashcards

Module 15.4 Compressors Flashcards

1
Q

What are the two main components of a compressor?

A
  • Stator
  • Rotor
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2
Q

What are the two types of compressor?

A
  • Axial flow
  • Centrifugal flow
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3
Q

What is the purpose of the stator vanes?

A
  • Guide and slow airflow to increase pressure
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4
Q

What are stator vanes in front of a compressor called?

A

Inlet Guide Vanes (IGV’s)

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5
Q

Stator vanes in the fan duct are usually named what?

A

Outlet guide vanes

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6
Q

How many stages are centrifugal compressors limited to due to efficiency concerns?

A

Two

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7
Q

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

A

Impeller and diffuser

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8
Q

In centrifugal compressors what can be said about the rise per stage?

A

High pressure rise

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9
Q

What are the two types of impeller fan?

A
  • Single entry
  • Double entry
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10
Q

What can be said about double entry impellers?

A

Smaller diameter but require a higher rpm

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11
Q

Where are centrifugal compressors commonly used?

A
  • Turboprop
  • Turboshaft
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12
Q

What shape are the compressor blades?

A

Aerofoil shaped

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13
Q

What does a gradual decrease in diameter of the rotating drum maintain?

A

Steady axial velocity

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14
Q

Two spools is much more suitable for what type of engine?

A

Dual flow

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15
Q

In a 3 spool engine what does the fan also act as?

A

Low pressure compressor

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16
Q

What is the purpose of the stators?

A
  • Act as guide vanes
  • Act as diffusers
17
Q

To achieve high compression in axial flow what is required?

A

Lots of stages

18
Q

Why is it beneficial to have a centrifugal compressor in an APU?

A
  • Low start up power
19
Q

What is the compression ratio from one stage to the next in an axial compressor?

A

1.1 to 1.2 to 1.3 (1.3 mentioned in 15.5)

20
Q

Does fan blade balancing require engine disassembly?

A

No

21
Q

The centrifugal force depends on what?

A
  • Rotation speed
  • Mass of the object
  • Distance between CoG and the rotational axis
22
Q

What is the moment weight?

A

Product of the blade’s mass and the distance of the CoG from the rotational axis

23
Q

Do blades have the same moment weight if they have the same mass?

A

No, not necessarily

24
Q

What numbers will be displayed on the root?

A
  • Part no.
  • Serial no.
  • Moment weight
25
Q

How are the fan discs matched?

A

Computerised balancing

26
Q

No.1 fan blade position is identified by what?

A
  • Index mark on fan disc
  • Offset hole
27
Q

What are the two methods of fan blade change?

A
  • Replace blade with one of moment weight extremely close to the opposite fan blade (pair)
  • Replace the pair
28
Q

What effect does increasing rotor speed have on the angle of attack?

A

Increases the angle of attack

29
Q

If relative airflow speed increases what effect does this have on the AoA?

A

Decreases the AoA

30
Q

What is the AoA between in the compressor?

A

Chord line of the vane and resultant rotor inlet velocity

31
Q

A low AoA ensure what?

A

Airflow into the rotor is smooth

32
Q

What is a compressor stall?

A

Airflow separation on the vanes

33
Q

How do compressor stalls occur?

A

Rapid decrease of airflow causes stall on some blades or stages

Stall causes a blockage in airflow

Low pressure zones, airflow stops and reverses

34
Q

What are some reasons for stall and surge?

A
  • Dents or ice
  • Damaged blades
  • Damaged or broken combustor
  • Damaged turbine components
  • Speed of engine below designed operating speed
  • Incorrect acceleration or deceleration
35
Q

What are the 3 methods to prevent compressor stall or surge?

A
  • Compressor bleed valves
  • Dual or triple spool
  • Variable compressor stator vanes
36
Q

Where are bleed valves found?

A

Mid compressor section sometimes aft compressor section as well.

37
Q

When are engine bleed valves open?

A

Low engine speeds

38
Q

What is the most effective method of preventing compressor stall?

A

Variable stator vanes

39
Q

If the pressure ratio is 1.3:1 and the air pressure to stage 1 is 10 psi. What is the input pressure into stage 2?

A

13 psi

CAA Module 15 (18 decks)

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