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M15 > 15.6 > Flashcards

15.6 Flashcards

1
Q

The turbine drives what?

A

The compressor and gear box

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2
Q

Two types of turbines?

A

Radial flow turbine
Axial flow turbine

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3
Q

What is the first main component of turbine?

A

A set if stationary vanes
-called the turbine nozzle guide vanes

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4
Q

What type of turbine is only used in the APU?

A

Radial flow turbine

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5
Q

What type of turbine is mainly used on modern engines?

A

Axial flow turbines

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6
Q

Explain operation of turbine

A

Turbine converts gas energy from combustion chamber to torque
Gas flow comes from combustion chamber and passes through nozzle guide vanes
Gas flow from combustion chamber is accelerated due to convergent ducts
Deflects towards the direction if rotation of turbine blades and causes it to rotate

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7
Q

A turbine which makes the rotation only by gas flow impact on rotor is known as what?

A

Impulse turbine

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8
Q

Impulse reaction turbine is often referred to as what?

A

Reaction turbine

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9
Q

What determines the service life of turbine?

A

The loads it takes

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10
Q

Turbine materials must be able to withstand what?

A

Extremely high heat and centrifugal forces due to high RPM

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11
Q

What are two factors that reduce service life of an engine?

A
  1. Material fatigue caused by power cycles (reduced by correct engine operation)
  2. Corrosion caused by sulphuric acid (sulphur is from fuel and high gas temperatures)
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12
Q

Why do blades elongate?

A

High centrifugal loads (Increased by heat)

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13
Q

What is creep?

A

The material deformation when centrifugal loads are applied over long period of time
(This deformation doesn’t return back)

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14
Q

What is a opposing factor that makes it hard to stop blade deformation?

A

High turbine inlet temperatures are required however, to stop deformation low temperatures are needed.

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15
Q

Why are turbine cooled?

A

Increase service life
Increase efficiency

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16
Q

What is convection cooling?

A

Easiest method of turbine cooling
Air from compressor is pushed onto blades to cool then pushed into the airstream

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17
Q

What is the cooling method for the turbine nozzle guide?

A

Impingement cooling

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18
Q

Why is film cooling the most preferred cooling method?

A

Reaches maximum cooling effect with minimum cooling air

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19
Q

First stage nozzle guide vanes are cooled by what?

A

Convection
Impingement
Film cooling

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20
Q

The first stage rotor blades are cooled by what?

A

Convection
Impingement
Film cooling

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21
Q

The second stage nozzle are cooled by what?

A

Convection
Impingement

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22
Q

The second stage rotor is cooled by what?

A

Convection only

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23
Q

Turbine clearance control does what?

A

Keeps tip clearance as small as possible in all operating conditions

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24
Q

What are the two reasons that turbine casing expands faster than the turbine rotor?

A

Turbine casing is thinner
Turbine casing is in contact with higher temperature areas

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25
Q

Is the expansion of a material by centrifugal force bigger than expansion by heat?

A

Yes

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26
Q

How are turbine cases cooled in a passive control system?

A

Cooled by a continuous airflow that is not regulated

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27
Q

Sources of cooling for high pressure turbines in passive clearance system?

A

Uses air from last stages of high pressure compressor as the cooling source

28
Q

Sources of cooling for low pressure turbine in passive clearance control?

A

Fan air

29
Q

How does active clearance control differ from passive clearance control?

A

Use the same air but active clearance control, controls the quantity of air

30
Q

Tip clearance control saves what?

A

Lots of fuel

31
Q

On engines with hydro-mechanical control units, the active clearance control system only operates when?

A

During climb and rise

32
Q

A hydro-mechanical engine control unit uses two signals to activate what?

A

Clearance control system

33
Q

The turbine section of a typical twin spool engine consists of what?

A

A high pressure turbine (HPT)
A low pressure turbine (LPT)
A turbine frame

34
Q

A typical stator assembly has what components?

A

Stator case
Nozzle guide vanes
Sealing and wall segments
Clearance control air manifolds

35
Q

High pressure turbine cases are usually in how many pieces?

A

One piece

36
Q

How are nozzle guide vanes held in place?

A

Nozzle guide vane support

37
Q

Each segment usually has how many nozzle guide vanes?

A

2

38
Q

The interstage seal prevents what?

A

Gas flow through the gap between stator and rotor

39
Q

Modern turbo fan engines have what around high pressure turbine case?

A

Cooling air tubes

40
Q

The cooling air tubes around the high pressure turbine case are used for what?

A

Active clearance control

41
Q

Why are there borescope ports in the turbine case?

A

For inspecting of rotor blades

42
Q

Low pressure turbine case is bolted to what?

A

To the rear flange of high pressure turbine

43
Q

LP turbine usually made of how many pieces?

A

One peice
Some engines have split stator cases

44
Q

The inner seals are located where on nozzle guide vanes?

A

Inner surface

45
Q

In low pressure turbines the segments are made up of how many vanes?

A

6 or 7

46
Q

The high pressure turbine rotor has what main components?

A

Turbine discs
Rotor blades
Rotating interstage seal
Forward and rear blade retainers

47
Q

What do the turbine discs do?

A

They hold the rotor blades and transfer torque from blades to compressor rear shaft

48
Q

How big is the cross sectional area of the turbine discs and why?

A

Very large
Discs must withstand high centrifugal loads

49
Q

The interstage seal acts as what between the discs?

A

A spacer

50
Q

The blade retainers are designed to hold what in place and why?

A

Hold the turbine blades in place
So they do not move from their seats due to gas loads

51
Q

What type of retainers are in LP turbines?

A

Strip type blade retainers
-they fit into dovetail slots and bent up at each end

52
Q

High pressure turbine uses what type of connection to attach blade to disc and why?

A

Fir tree root
As they have lots of contact points

53
Q

What are the two types of blades used in modern gas turbine engines?

A

Open end blades-high rotational speed turbines
Shrouded blades- found in some high pressure turbines

54
Q

Shrouded blades form what around the tips of rotor blades?
What does this help with?

A

Forms a band
Helps reduce vibrations

55
Q

What type of seal is used around outer surface of shroud seal?

A

Knife edge seals

56
Q

What is an advantage of a knife edge seal?

A

Help reduce air loss at tip of blades

57
Q

What is a disadvantage of knife edge seals?

A

Adds more weight

58
Q

The added weight of a shrouded blades can be offset by what?

A

Thinner blades?

59
Q

Turbine discs are either directly splined or bolted to what?

A

Drive shaft

60
Q

High pressure blades are internally cooled by what?

A

By air from HP compressor

61
Q

The turbine frame supports what?

A

Turbine rotors

62
Q

Two functions of turbine frame?

A

Supports turbine rotors
Provide attachment points for rear engine mount

63
Q

A typical turbine frame is built of what?

A

Frame hub with bearing support
Outer frame casing
Set of struts which connects the hub with the outer casing

64
Q

Two arrangements of struts on gas turbine engine?

A

Radial struts
Tangential struts

65
Q

Radial struts are designed how and why?

A

Designed short as possible
Minimises expansion of struts

66
Q

Tangential struts minimise stress by thermal expansion how?

A

If they thermally expand, they cause the hub to rotate slightly

M15 (18 decks)

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