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M15 Ryan > M15.6 > Flashcards

M15.6 Flashcards

1
Q

What are the 2 types of turbines?

A

Radial flow
Axial flow

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2
Q

What is the main purpose of the turbine?

A

To provide power to drive the engine compressor and gear box

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3
Q

What is the turbine made up of?

A

Rotors
Stators

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4
Q

Radial turbines are always what?

A

Single stage turbines

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5
Q

Where are radial flow turbines used?

A

On small GTE’s such as APU

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6
Q

What are the disadvantages of a radial flow turbine?

A

Small efficacy
Small airflow

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7
Q

What is the advantage of radial flow turbine?

A

Simple design

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8
Q

The axial flow turbine is mainly used on what?

A

Modern GTE’s

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9
Q

What is the advantage of axial flow turbines?

A

Allow for very high airflow

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10
Q

What is the operation of a turbine?

A

To convert gas into torque

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11
Q

What’s the purpose of the convergent duct?

A

To accelerate the air and create more pressure energy

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12
Q

What is a impulse turbine?

A

Makes rotation only by impact of gas flow on rotor blades

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13
Q

Where are impulse turbines usually found?

A

On very old GTE’s

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14
Q

Where is the highest heat to metal contact in the engine?

A

1st stage of hp compressor

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15
Q

What are the 2 types of turbine blades?

A

Impulse
Impulse - reaction

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16
Q

The force at the outlets acts in what direction?

A

Opposite to discharge gas flow

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17
Q

What is done by the pilot to try and reduce heat in the turbine?

A

High throttle is kept to a min

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18
Q

Why must the correct jet fuel be used?

A

Prevent corrosion from sulphuric acid

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19
Q

What are the 3 factors that contribute to creep?

A

Time
Temp
Centrifugal forces

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20
Q

When does creep occur?

A

When centrifugal forces are applied for a long time in high temps

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21
Q

What is the only way to reduce creep?

A

To keep material as cool as possible

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22
Q

What are the 2 reasons to cool turbines for?

A

Increase service life
Better turbine efficiency

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23
Q

What are the nozzle guide vanes and rotor blades cooled from?

A

Air from hp compressor

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24
Q

What is convention cooling?

A

Passing cool airflow through the hollow turbine materials while air is also passing inner wall of turbine aero foil

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25
Q

What is the easiest method of cooling?

A

Convection cooling

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26
Q

What is the best cooling method for nozzle guide vanes no rotor blades?

A

Impingement cooling

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27
Q

What is the most effective method of cooling?

A

Film cooling

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28
Q

What is the principle of film cooling?

A

Prevents direct contact of hot gas flow with turbine materials

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29
Q

What method is used to cool second stage hide vanes?

A

Convection
Impingement

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30
Q

What method is used to cool second stage rotor blades?

A

Convection

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31
Q

What is tip clearance?

A

The gap between the tip of the rotor blade and the casing

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32
Q

Why does a large tip clearance decrease the efficacy of the turbine stage?

A

Because a large amount of gas passes through the gap between the rotor blades and turbine casing

33
Q

What are the 2 types of turbine clearance control systems?

A

Passive clearance control
Active clearance control

34
Q

How is vibration reduced in LP turbine blades?

A

With shrouds

35
Q

What causes stress rupture cracks in the turbine section?

A

Metal fatigue and corrosion

36
Q

When does the active clearance control system operate on engines fitted with hydro mechanical fuel control systems?

A

During climb and cruise

37
Q

What does the passive clearance control system use for cooling?

A

Fan air

38
Q

What controls clearance control valves?
And what are they actuated by?

A

Engine control unit
Actuated by the fuel pressure from the hydro mechanical unit

39
Q

Are the LP turbine blades cooled?

A

No

40
Q

FADEC?

A

Full Authority Digital Engine Control

41
Q

What works out the tip clearance?

A

ECU

42
Q

What loads does the turbine frame carry?

A

Bearing loads of aft end of the LP turbine

43
Q

The case of the HP turbine is bolted to what?

A

Rear flange of combustion case

44
Q

How many pieces make up the HP turbine case?

A

1

45
Q

Why is the HP turbine case made up of a abradable ceramic surface?

A

To give thermal resistance

46
Q

How many nozzle guide vanes are in a nozzle guide vane segment?

A

2

47
Q

What are the gaps between the nozzle guide vane segments sealed with?

A

Sealing metallic strips

48
Q

What does the interstate seal do?

A

Prevents airflow between the rotor and stator gap

49
Q

Where is the HP turbine case bolted to?

A

The rear flange of HP turbine

50
Q

The LP turbine case is made of how many pieces on modern engines?

A

1

51
Q

Where are the inner air seals located?

A

On the inner surface of the nozzle guide vane segments

52
Q

How many vanes make up the nozzle guide vane segments?

A

6 or 7

53
Q

The HP turbine rotor is attached to what?

A

The rear shaft of the compressor

54
Q

What is the function of a disc on the turbine?

A

To hold the rotor blades and transfer torque

55
Q

Why is the cross sectional area of the disc very large?

A

So the disc withstands high centrifugal forces

56
Q

On HP turbines what must the interstate seal do?

A

Help transfer torque from stage 2 disc to stage 1 disc

57
Q

What does the interstate seal do?

A

Act as a space between the 2 discs

58
Q

What’s the purpose of the blade retainers?

A

Hold turbine blades in place

59
Q

What does the seal lip do on the blade retainers?

A

Act as air seal

60
Q

Why is the fur tree root fitting so efficient?

A

Has many contact surfaces

61
Q

What is the fitting like on fur tree roots when the engines not running?

A

Loose

62
Q

What is the most common method for attaching turbine rotor blades?

A

Fir tree root

63
Q

What advantage does the axial flow turbine have over radial flow turbines?

A

They can be built with as many stages as required and allow for a very high flow rate

64
Q

What is the primary air sources for a passive clearance control system?

A

HPC air for the HPT and fan air for LPT

65
Q

What are the 2 types of rotor assembly?

A

Open ended blades
Shrouded blades

66
Q

What type of blade is used in HP turbines?

A

Open ended blade

67
Q

What’s the disadvantage of shrouded blades?

A

More weight

68
Q

What’s the purpose of the knife edge seal on shrouded blades?

A

Helps reduce air loses at the tip of blade

69
Q

Where are shrouded blades usually found?

A

LP turbines

70
Q

How are turbine discs attached to the shaft?

A

Either splined or bolted

71
Q

How are the HP turbine blades cooled?

A

Internally with air from HP compressor

72
Q

What type of structure is the turbine frame?

A

Major

73
Q

What does the turbine frame do?

A

Supports 1 or 2 turbine rotors and provides attachment points to rear engine mount

74
Q

How are the turbine struts shaped?

A

Aerodynamically to cause a little drag as possible

75
Q

What are the 2 types of strut?

A

Radial strut
Tangential strut

76
Q

The radial strut is what?

A

Thick and hollow

77
Q

What does the tangential strut do to minimise stress from thermal expansion?

A

Expands

78
Q

On engine shut down what is the contraction sequence of the turbine and casing?

A

Rotor shrinks
Then
Casing

79
Q

On what stage of a turbine would open turbine blades normally be found?

A

On the HP turbine stage

M15 Ryan (17 decks)

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