Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

CAA Module 15 > Module 15.4 Compressors > Flashcards

Module 15.4 Compressors Flashcards

1
Q

What is the primary function of the compressor?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What must the compressor do to the air received from the inlet duct?

A

Increase the pressure of the mass of air, and then discharge it to the combustion chamber.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the secondary function of the compressor?

A

To supply air to the systems that require bleed air for operation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Locations of the bleed ports depend on what?

A

The pressure or temperature required by that system.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

The compressor has what two main components?

A

Compressor stator

Compressor rotor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does each rotor disk have on it?

A

Rotor blades

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What do the rotor blades do to the air as they rotate around the axis?

A

They suck in air and push it to the outlet side of the rotor. This increases the energy of the airflow.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the compressor stator?

A

A fixed component. The stator vanes guide and slow the airflow to cause an increase in pressure.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

The combination of a rotor and stator is called what?

A

A compressor stage.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What part is always the first part of the compressor stage?

A

The rotor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What stage compressor with two rotor-stator pairs

A

A two stage compressor.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

The space between each rotor and each stator is called what?

A

Annulus space

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

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

A

Inlet Guide Vanes (IGVs).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What do the Inlet Guide Vanes (IGVs) do?

A

Improve the airflow into the first compressor stage.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the stator vanes in the fan duct called?

A

Outlet Guide Vanes (OGVs).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What do Outlet Guide Vanes (OGVs) do?

A

Improve the (bypass) airflow into the fan nozzle.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are the two types of compressors?

A

Centrifugal flow compressor

Axial flow compressor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

The gap between each stator and each rotor forms what?

A

A divergent duct. This is done to decrease airflow velocity and increase pressure.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Rotor blades rotating around the axis does what to the velocity of the airflow?

A

Increases it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is happening to velocity as air goes from rotor to stator etc?

A

Velocity is constantly increasing and decreasing.

From the first to final stage, velocity has stayed the same but the pressure has increased.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What does the centrifugal-flow compressor consist of?

A

Impeller (rotor), diffuser (stator), and compressor manifold.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the pressure rise per stage with centrifugal compressors?

A

A high-pressure rise per. 8:1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How many stages are centrifugal compressors limited to?

A

Two stages due to efficiency concerns (pressure loss).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is the diffuser and manifold assembly called?

A

The diffuser

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Where is the impeller located?

A

Mounted on the shaft and inside the diffuser.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

How does the impeller work?

A

It accelerates air outwardly to the diffuser.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What two types of impeller can be used?

A

Single entry or double entry.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is one stage of the centrifugal compressor?

A

An impeller and diffuser together

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Why does a single entry impeller allow for over a double entry type?

A

More convenient ducting directly to the impeller eye (inducer vanes) as opposed to the more complicated ducting needed reach the rear side of the double-entry type.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Axial flow compressors are normally found on what type of engine?

A

Turbofan engines

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Centrifugal flow compressors are normally found on what type of engine?

A

Turboprop and turboshaft engines.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Define an axial flow compressor.

A

One that consists of one or more rotating components which have aerofoil-shaped blades attached.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

A rotor-stator pair in a centrifugal compressor is referred to as what?

A

A stage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What happens to the rotating drum and case from front to back in an axial compressor?

A

Diameter gradually decreases.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Why does the diameter of the drum and case decrease in an axial compressor?

A

To maintain a steady axial velocity (no stagnated air).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

What does a single-spool compressor consist of?

A

A single drum and multiple stators.

37
Q

Two spool are more suitable for what?

A

Dual flow engines.

38
Q

In a two spool, what is the front part of the compressor designed to do?

A

Initially compress a larger mass of air than the mass injected into the High Pressure (HP) compressor.

39
Q

In a triple spool engine, what is the fan driven by?

A

A dedicated segment of the turbine, making its shaft the Low Pressure (LP).

40
Q

What does the fan act as in a triple spool engine?

A

A low-pressure compression stage (slightly pressurising the air that goes into the core).

41
Q

Where is the smaller proportion of the flow, known as the core flow or hot air passed through?

A

The Intermediate Pressure (IP) and HP compressor, the combustion chamber, and the turbine.

42
Q

From one stage to the next in an axial compressor, the axial compression ratio is…

A

Small

43
Q

What is the typical compression ratio in an axial compressor?

A

Between 1:1 and 1:2.

44
Q

What is done to achieve a high compression rate in axial flow compressors?

A

A large number of stages.

45
Q

What does a spool consist of?

A

A turbine, shaft and compressor

46
Q

How many compressors in a twin spool?

How many in a triple spool?

A

Two in a twin spool and three in a triple spool.

47
Q

What two ways can rotors (blades) be balanced?

A

Statically and dynamically balanced.

48
Q

What is the moment if the rotors are dynamically balanced?

A

Moment is 0

49
Q

If a rotor blade is dynamically imbalanced, what is needed?

A

A balance weight on the opposite blade.

50
Q

All turbine engine rotating assemblies require balancing by who?

A

Manufacturer

51
Q

Which set of blades can be balanced without disassembly?

A

Fan blades

52
Q

When can the rotor of the engine run free of vibration?

A

If the fan blades that are opposite each other create identical centrifugal forces.

53
Q

The centrifugal force of fan blades depends on what three factors?

A

The rotor speed

The blade mass

The distance of the centre of gravity of the fan blade from the rotational axis

54
Q

Can fan blades have a different moment weight even if they have the same mass?

Why?

A

Yes, because the centre of gravity of each fan blade is different.

55
Q

What three measurements are their for moment weight?

A

gram inches

cm.g

ounce inches

56
Q

What three numbers does a fan blade root have?

A

Part number

Serial number

The moment weight

57
Q

How are blades with individual moment weights generally matched on the fan disc?

A

Using computerised balancing. The computer works out the best position for each blade on a fan disc.

58
Q

How is fan blade no.1 usually identified?

A

Index mark on the fan disc or an offset hole.

59
Q

How are the blades often numbered?

A

In the direction of rotation.

60
Q

What is the best method of changing a fan blade?

A

Replace the blade with a new blade that has a moment weight as close as possible.

61
Q

When would no further balancing be required after a fan blade change?

A

If the difference in moment weight between the old and new blade is small enough (as specified by the manufacturer).

62
Q

If the difference in moment weight between the old and new blade is larger than specified by the manufacturer, what should be done?

A

Balance weights can be used.

63
Q

What are balance weights used for when changing a blade?

A

To balance the difference in the moment weight of the old and new fan blades.

64
Q

Where are balance weights installed?

A

On the fan disc or in the spinner cone.

65
Q

What other method of changing fan blades are there?

A

Change a pair of blades (opposite blade) with similar moment weight blades, even if only one blade is damaged.

66
Q

Define the compression ratio of an internal combustion engine.

A

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

67
Q

Is compression ratio proportional to RPM?

A

No, but it does vary with RPM.

68
Q

What is the pressure ratio at each stage of an axial compressor?

A

1.3:1

69
Q

What does a 1.3:1 pressure ratio mean?

A

If the air pressure enters the first stage with 10 psi, then the air pressure is increased to 13 psi on the output side of that compressor stage.

This pressure now becomes the input pressure to the next stage.

70
Q

What is the pressure ratio like at each stage of the compressor in axial flow compressors?

A

Very small

71
Q

What three methods are there to prevent a compressor stall?

A

Bleed valves

Dual or triple-spool rotors instead of single spool

Variable compressor stator valves

72
Q

How do bleed valves prevent a compressor stall?

A

They are open at low engine speeds (RPM) so that the excessive airflow from the forward stages can escape overboard.

73
Q

Where would bleed valves be placed in multi-stage axial compressors?

A

At several positions

74
Q

Where is the bleed air bled of to?

A

C-duct (bypass duct)

75
Q

Where would a 3rd stage bleed valve be?

A

3rd stage of the compressor.

76
Q

On a dual spool engine, what is the fwd and aft compressor called?

A

Fwd - Low-pressure compressor or N1 compressor.

Aft - High-pressure compressor or N2 compressor

77
Q

What is the most effective method to prevent compressor stall?

A

Variable stator vanes and variable inlet guide vanes

78
Q

Where are variable stator vanes and variable inlet guide vanes located?

A

In the forward stages of the high-pressure compressor.

79
Q

What is the advantage of variable stator vanes?

A

An optimum angle of attack on the following rotor blades can be reached for every engine speed.

80
Q

What does the angle of attack of the rotor depends on?

A

Air inlet velocity and rotor speed.

81
Q

What does the correct relationship between the inlet velocity and the rotor speed allow?

A

A smooth air flow.

82
Q

What does the angle of attack of the rotor blades need to be for smooth airflow

A

Small

83
Q

When does the angle of attack of the rotor blade change?

A

When the inlet air velocity decreases (rotor speed/rpm is now too fast for inlet velocity).

84
Q

What is a compressor stall?

A

When airflow separates from the compressor aerofoils and causes a turbulent vortex.

85
Q

What does a compressor stall do to the air?

A

Causes the airflow to slow down, stop or reverse its direction.

86
Q

What is a compressor stall?

A

A very severe form of compressor stall. Surge can happen on all engine compressors.

87
Q

Where can compressor surges occur?

A

In the forward or the aft compressor stages.

88
Q

What does a surge in the fwd compressor stages affect?

A

Only a part of the compressor blades due to the bigger dimensions of the blades.

89
Q

How does a surge affect the aft compressor stages?

A

It develops very rapidly over a large part of the compressor.

CAA Module 15 (18 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions