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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
Is the expansion of a material by centrifugal force bigger than expansion by heat?
Yes
26
How are turbine cases cooled in a passive control system?
Cooled by a continuous airflow that is not regulated
27
Sources of cooling for high pressure turbines in passive clearance system?
Uses air from last stages of high pressure compressor as the cooling source
28
Sources of cooling for low pressure turbine in passive clearance control?
Fan air
29
How does active clearance control differ from passive clearance control?
Use the same air but active clearance control, controls the quantity of air
30
Tip clearance control saves what?
Lots of fuel
31
On engines with hydro-mechanical control units, the active clearance control system only operates when?
During climb and rise
32
A hydro-mechanical engine control unit uses two signals to activate what?
Clearance control system
33
The turbine section of a typical twin spool engine consists of what?
A high pressure turbine (HPT) A low pressure turbine (LPT) A turbine frame
34
A typical stator assembly has what components?
Stator case Nozzle guide vanes Sealing and wall segments Clearance control air manifolds
35
High pressure turbine cases are usually in how many pieces?
One piece
36
How are nozzle guide vanes held in place?
Nozzle guide vane support
37
Each segment usually has how many nozzle guide vanes?
2
38
The interstage seal prevents what?
Gas flow through the gap between stator and rotor
39
Modern turbo fan engines have what around high pressure turbine case?
Cooling air tubes
40
The cooling air tubes around the high pressure turbine case are used for what?
Active clearance control
41
Why are there borescope ports in the turbine case?
For inspecting of rotor blades
42
Low pressure turbine case is bolted to what?
To the rear flange of high pressure turbine
43
LP turbine usually made of how many pieces?
One peice Some engines have split stator cases
44
The inner seals are located where on nozzle guide vanes?
Inner surface
45
In low pressure turbines the segments are made up of how many vanes?
6 or 7
46
The high pressure turbine rotor has what main components?
Turbine discs Rotor blades Rotating interstage seal Forward and rear blade retainers
47
What do the turbine discs do?
They hold the rotor blades and transfer torque from blades to compressor rear shaft
48
How big is the cross sectional area of the turbine discs and why?
Very large Discs must withstand high centrifugal loads
49
The interstage seal acts as what between the discs?
A spacer
50
The blade retainers are designed to hold what in place and why?
Hold the turbine blades in place So they do not move from their seats due to gas loads
51
What type of retainers are in LP turbines?
Strip type blade retainers -they fit into dovetail slots and bent up at each end
52
High pressure turbine uses what type of connection to attach blade to disc and why?
Fir tree root As they have lots of contact points
53
What are the two types of blades used in modern gas turbine engines?
Open end blades-high rotational speed turbines Shrouded blades- found in some high pressure turbines
54
Shrouded blades form what around the tips of rotor blades? What does this help with?
Forms a band Helps reduce vibrations
55
What type of seal is used around outer surface of shroud seal?
Knife edge seals
56
What is an advantage of a knife edge seal?
Help reduce air loss at tip of blades
57
What is a disadvantage of knife edge seals?
Adds more weight
58
The added weight of a shrouded blades can be offset by what?
Thinner blades?
59
Turbine discs are either directly splined or bolted to what?
Drive shaft
60
High pressure blades are internally cooled by what?
By air from HP compressor
61
The turbine frame supports what?
Turbine rotors
62
Two functions of turbine frame?
Supports turbine rotors Provide attachment points for rear engine mount
63
A typical turbine frame is built of what?
Frame hub with bearing support Outer frame casing Set of struts which connects the hub with the outer casing
64
Two arrangements of struts on gas turbine engine?
Radial struts Tangential struts
65
Radial struts are designed how and why?
Designed short as possible Minimises expansion of struts
66
Tangential struts minimise stress by thermal expansion how?
If they thermally expand, they cause the hub to rotate slightly

M15 (18 decks)

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