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M15 > M15.4 > Flashcards

M15.4 Flashcards

1
Q

What does the rotor do in the compressor?

A

Sucks in air and pushes it to the outlet side of the rotor

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2
Q

What do stator vanes do?

A

Guide and slow the airflow to increase pressure

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3
Q

What comes first the rotor or the stator?

A

The rotor

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4
Q

What is the job of a inlet and outlet case?

A

To improve and straighten the airflow into the compressor

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5
Q

How many stages of centrifugal flow compressors are the most effective?

A

Two stages

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6
Q

What is meant by double entry type impeller (double face compressor)?

A

Two compressors face to face

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7
Q

Why is a double entry type impeller used on APUs?

A

Because it has a higher airflow at a smaller diameter which saves weight.

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8
Q

What are the channels between the rotor blades (in the stator stages) called?

A

Diffusers (increase static pressure)

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9
Q

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

A

1.3:1 (enters at 10psi leaves at 13psi)

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10
Q

Why does the compressor cross section decrease through out the compressor?

A

Because as the airflow gets compressed the pressure and density increases so the air needs less volume

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11
Q

What is the difference between axial flow compressors and centrifugal flow compressors?

A

Axial flow keeps it going in a straight line but a centrifugal pushes it out to the side

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12
Q

What is the design point of compressors?

A

The optimum operating condition

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13
Q

What is the resultant rotor inlet velocity?

A

The relationship between the inlet velocity and the rotor speed

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14
Q

What does compressor stall do to the airflow inside?

A

It can slows down, stop, or reverse its direction

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15
Q

What is compressor surge?

A

When there are multiple compressor stalls on the rotors of the compressors

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16
Q

What happens if there is a compressor surge in the first few stages of the compressor?

A

It usually affects only a part of the compressor blades due to there large diameter

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17
Q

How is compressor stall and surge caused?

A

By problems i engine operation or by damaged components

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18
Q

What happens if the air piles up in the compressors?

A

The air slows down too much and creates a stall or surge

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19
Q

What would fast acceleration lead to?

A

Too much fuel in the combustion chamber which increase back pressure

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20
Q

What is used to prevent stall and surge in a compressor?

A
  • compressor bleed valves
  • use dual or triple pool rotors
  • variable compressor stator vanes
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21
Q

Where are compressor bleed valves found?

A

In the mid or aft section of the compressor

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22
Q

How do compressor bleed valves work?

A

They would open at low engine speeds for excessive airflow from the forward stages

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23
Q

What is the most effective method to prevent stall?

A

Variable stator vanes (they can change there angle of attack so it can always operate at optimum efficiency)

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24
Q

Where would variable stator vanes be found?

A

In the forward stages of the high pressure compressor

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25
Q

What is the main disadvantage of variable stator vanes?

A

They’re a very complicated control mechanism

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26
Q

What is the job of the fan blades?

A

To provide initial compression and then pass the compressed air to the engine primary and secondary gas paths

27
Q

What is the job of the low pressure compressor and low pressure turbine couplings?

A

To secure them to the low pressure shaft

28
Q

What is the job of a fan stator case?

A

To give a flow path for the fan discharge air

29
Q

Why is the spinner cone curved or sharp?

A

Because they’re the best shapes to prevent ice build up

30
Q

Why do some spinner cones have a soft tip?

A

To cause a small imbalance during operation which prevents large ice build up

31
Q

Why is there a spiral on the spinner cone?

A

To show if it’s rotating and to share birds away

32
Q

Where are balance eights attached?

A

To the mounting bolts of the spinner cone

33
Q

What type of fitting do the fan blades use to sit in the fan rotor disc?

A

Dovetailed fitting

34
Q

Why is there a loose fit between the blade root and blade seat?

A

So that sudden forces or torque loads do not exceed the maximum allowable stress

35
Q

When flan blades are suddenly hit they deflect rear wards and forwards, whys this?

A

Because they can slide and cause friction which dampens the blade fluttering

36
Q

Why is the shroud surface covered in a special coating?

A

To make sure they can slide on a dry surface which will leads to a breakage

37
Q

Where is a fan shroud located?

A

Mid way up the blade

38
Q

Why don’t wide chord fan blades have shrouds?

A

Because of the strength of the wide fan blade

39
Q

What is special about the wide chord fan blade?

A

It has hollow sections in the blade

40
Q

What is another name for low pressure compressor?

A

A Booster module

41
Q

What are the two types of construction for compressor stator cases?

A

Closed stator case and a split stator case

42
Q

Why are there multiple ring elements (flanges) on the outer surface of the case?

A

To help stiffen and prevent deformation

43
Q

What are the lining elements on the inner surface of the fan case called and why are they used?

A

Acoustic panels and they have small holes to reduce noise

44
Q

Why is an abrasive shroud used on the inner fan case?

A

To prevent damage to the fan blade tips when they come in contact at high speeds

45
Q

What is the flan blade containment area made out of?

A

A ring of honeycomb construction covered in Kevlar

46
Q

What are outlet guide vanes in the fan duct normally made out of?

A

Aluminium or composite

47
Q

What main component can be found in between the low pressure compressor an high pressure compressor?

A

The fan frame (also known as intermediate case)

48
Q

Where would you find the forward engine mount?

A

The aft side of the fan fram

49
Q

why are the fan frame struts hollow?

A

To save weight

50
Q

How is the moment of a fan blade worked out?

A

By using a special blade scale

51
Q

Where would you find the moment weight on a fan blade?

A

On the blade root

52
Q

What can be found on the blade root?

A
  • a part number
  • a serial number
  • a moment weight
53
Q

What is meant by computerised balancing?

A

When a computer works out the location of the fan blades for balancing reasons

54
Q

What way round are most engine fan blades numbered?

A

The way of rotation

55
Q

What are the methods to change a sinGle fan blade?

A
  • Get the moment weight as close to the old blade as possible
  • if the difference is too high add balance weights
  • change the one blade and the opposite one
56
Q

Where is the compressor outlet case found?

A

Between the last compressor and the combustion chamber

57
Q

What is another name for the compressor outlet case?

A

The diffuser case

58
Q

What is the older way of constructing a compressor rotor?

A

The use of discs and spacers which are put together using tie rods

59
Q

What is the new way of constructing a compressor rotor?

A

By using multiple integral drums

60
Q

Where is the rear drum bolted to?

A

The rear hub

61
Q

Where is the CDP seal located and what does it do?

A

It’s located behind the last compressor stage and is used to prevent discharge of airflow from escaping into the bearing area

62
Q

What are the three ways of connecting a fan blade to the fan disc?

A
  • axial dovetail slot
  • circumferential dovetail slot
  • locking bolt slot
63
Q

What forces does the front compressor case support?

A

Bending and torsion

64
Q

What is used inside a high compression ratio?

A

Variable stator vanes in the first stages

M15 (15 decks)

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