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M15 > 15.4 > Flashcards

15.4 Flashcards

1
Q

Compressors are made up of what?

A

Stators and rotors

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2
Q

What pressure do rotors increase?

A

Dynamic pressure

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3
Q

Stator vanes do what?

A

Slow airflow and increase pressure

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4
Q

Which is first in compressor stage out of rotors and stators?

A

Rotors

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5
Q

What are stator vanes also known as?

A

Inlet guide vanes (IGV)

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6
Q

Two types of compressors?

A

Axial flow
Centrifugal flow

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7
Q

What are the main components of a centrifugal compressor?

A

The impeller
The diffuser
The compressor manifold

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8
Q

Centrifugal flow compressors give what pressure ratio?

A

5:1

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9
Q

How many compressor stages are efficient?

A

2

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10
Q

Two impellers mounted back to back are known as what?

A

Double face compressor

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11
Q

What are the benefits of double face compressors?

A

Increase airflow due to two sides
Saves weight

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12
Q

Airflow in axial flow compressor is on what axis?

A

Horizontal axis

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13
Q

As pressure increases, density….

A

Increases

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14
Q

You taper axial flow compressors why?

A

Maintain air velocity

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15
Q

Why are compressors sensitive to airflow change?

A

Because compressors only have one operating condition for a given pressure ratio, rotational speed and airflow

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16
Q

What is the direction of airflow better called?

A

The resultant rotor inlet velocity

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17
Q

The resultant rotor inlet velocity is a result of what?

A

Air inlet velocity and rotor speed

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18
Q

The angle of attack changes when?

A

If rotor speed or inlet velocity changes

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19
Q

Compressor stall causes what for airflow in the compressor?

A

Causes airflow to slowdown, stop or reverse direction

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20
Q

A compressor surge is a very severe what?

A

Compressor stall

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21
Q

How is a compressor surge generated?

A

Rapid decrease of airflow onto blades
Then stall causes a blockage
That then causes low pressure zones

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22
Q

Surge is forward phase affects what?

A

Compressor blades

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23
Q

A surge in the aft stages could cause what to happen?

A

A reverse flow
Could occur from combustion chamber back to engine inlet

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24
Q

What are reasons for stalls and surges?

A

Dents or ice that cause disrupted airflow
Damaged rotor blades could cause disrupted airflow
Dirty compressor blades

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25
Q

How does a fast deceleration cause similar problems on dual to triple spool engines?

A

The rotor speed of high pressure compressor decreases faster than that of low pressure compressor

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26
Q

What is a method to avoid stalls or surges?

A

Use of dual or triple spools

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27
Q

Where are bleed valves found in compressors?

A

Found in mid and sometimes aft section of compressor

28
Q

Why would you open the bleed valves at slow speeds?

A

So excessive airflow from forward stages can escape overboard

29
Q

What are the low speed and high speed compressors driven by?

A

Their respective turbines in latter stages of engine

30
Q

Variable stator vanes in compressor are used to prevent what?

A

Stall- Along vertical axis

31
Q

The spinner cone is also known as what?

A

Compressor inlet or nose cone

32
Q

Why do engines have a spinner cone?

A

-creates smooth aerodynamic fairing at engine inlet
-soft tip causes small imbalance to prevent ice build up
-heated on some engines

33
Q

What type of attachment is the fan blade attachment?

A

Dovetailed fitting

34
Q

Two loads on rotor blades?

A

Air loads
Centrifugal loads

35
Q

What is the function of shrouds?

A

Keeps fan blade from deflection, within safe limits when heavy loads are on them
Converts energy of fluttering to friction

36
Q

Why are wide chord fan blades more efficient than conventional blades?

A

They run with lower speed which reduces noise
Flexible
Can withstand FOD better than conventional

37
Q

Low pressure compressor is also known as what?

A

Booster modules

38
Q

Rotor drum of low pressure compressor is attached to what?

A

Fan disc

39
Q

Between dovetail slots there are rings with sharp edges to create what?

A

A labyrinth seal

40
Q

What are two methods of making shroud assembly?

A

Made from plain metal surfaces
Or individual segments

41
Q

Shroud assembly segments are made up of what?

A

Filled with soft, abradable material where knife edges can cut in

42
Q

On modern turbofan engine the fan cause has one or more ring elements, how are they bolted?

A

They’re bolted together to flanges
-Flanges help stiffen the case and prevent deformation

43
Q

Acoustic panels provide what?

A

Smooth airflow
Reduce noise

44
Q

The fan blade containment prevents what?

A

A fan blade from penetrating the fan case if it breaks during high speed operation

45
Q

What are some things that would affect centrifugal force?

A

Rotor speed
Blade mass
Distance of the COG of fan blade from rotational axis

46
Q

Moment weight can be given in what values?

A

Gram inches
CMG
ounce inches

47
Q

What is the moment of weight?

A

The product of blade mass and distance of COG from rotational axis

48
Q

How is moment of weight worked out?

A

Worked out by special blade scale

49
Q

How is fan number one identified?

A

Index mark on fan disc or by an offset hole

50
Q

Where are balance weights installed?

A

On fan disc or in spinner cone

51
Q

A typical high pressure compressor consists of what?

A

Rotor drum
Forward hub
Rear hub
Rotor blades mounted on a drum

52
Q

What is CDP?

A

Compressor discharge pressure

53
Q

The compressor discharge pressure (CDP) prevents what?

A

Prevents the compressor discharge airflow from escaping into the bearing area below the combustion chamber

54
Q

Blades held in by blade retainers prevents what?

A

Prevents axial movement

55
Q

How are rotor blades secured?

A

Locking lug

56
Q

The high pressure compressor case is split into what?

A

Front compressor case
Rear compressor case

57
Q

The front compressor case supports what loads?

A

Structural loads
Torsion
Bending

58
Q

Variable stator vanes have what at each end?

A

Trunnion

59
Q

The HP compressor is a source of pressurised air for what?

A

Pneumatic systems
Engine related purposes

60
Q

Bleed air is supplied through what?

A

Hollow stator vanes

61
Q

Bleed manifolds collect bleed air and do what?

A

Supply it to consumers

62
Q

What are the fixed axial flow compressor aerofoils in an aircraft gas turbine engine called?

A

Stators

63
Q

What is the function of the stator vane assembly at the discharge end of a typical axial flow compressor?

A

To straighten airflow to eliminate turbulence

64
Q

Where does the pressure increase in an axial compressor stage?

A

In both the rotor and the stator

65
Q

Why do the compressor stators in a gas turbine engine act as diffusers?

A

To decrease velocity in the gas flow

66
Q

What is known as the design point of a gas turbine engine?

A

Optimum RPM the engine can operate at

67
Q

Which installed components can prevent compressor stalls?

A

Bleed valves, multiple spools and variable stator vanes

M15 (18 decks)

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