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Module 15 > 15.6 > Flashcards

15.6 Flashcards

(85 cards)

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1
Q

What is the sole purpose of the gas turbine?

A

To absorb 60-70% of the energy

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2
Q

Two types of turbine on GTE?

A

Axial flow
Radial Flow

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3
Q

What is always the first main component of a turbine?

A

Stationary vanes

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4
Q

What is another name for these stationary vanes?

A

Turbine nozzle guide vanes

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5
Q

What are the rotors connected to?

A

Turbine disc

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6
Q

What turbines are always single stage?

A

Radial flow

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7
Q

Where are radial flow turbines normally used?

A

Small GTE such as the APU

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8
Q

Advantages of Radial flow turbines?

A

They are simple design and easy to manufacture

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9
Q

What are the the disadvantages of Radial turbines and what does this mean?

A

Only allow small airflows so are less efficient

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10
Q

Why in the radial flow turbine is only small amounts of airflow allowed making it inefficient?

A

High Aerodynamic losses and airflow must enter against centrtifugal fores

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11
Q

Where are axial flow turbines mainly used?

A

In a modern GTE

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12
Q

How many stages are axial flow turbines limited to?

A

As many as is necessary to operate compressor

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13
Q

What is an advantage of axial turbines?

A

They allow high amounts airflow to create high thrust

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14
Q

What does the turbine convert the gas energy to?

A

Torque

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15
Q

What is used to accelerate the gas flow from the combustion chamber?

A

Convergent duct

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16
Q

Where is the convergent duct?

A

Between nozzle guide vanes

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17
Q

What is an impulse turbine and how is it recognised?

A

A turbine which makes the rotation only by the impact of the gas flow on the rotor blades, recognisable by the special shape of the rotor blades

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18
Q

What are the 3 types of rotor blades?

A

Pure Impulse configuration
Pure Reaction configuration
Reaction-Impulse configuration

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19
Q

In a pure impulse type turbine where does the total pressure drop occur and why?

A

The fixed nozzle guide vanes because of their convergent shape

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20
Q

What does all the edgy convert to after hitting the rotor blade?

A

Kinetic energy

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21
Q

In a reaction configuration what are the fixed nozzle guide vanes designed to do?

A

Alter the gas flow direction without changing pressure

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22
Q

What (to do with the gas) causes the rotor to spin in a pure reaction type turbine?

A

Expansion and Acceleration of the gas

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23
Q

What type of duct is involved in Reaction impulse (reaction) turbine?

A

Convergent

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24
Q

What happens to the velocity and pressure in a reaction impulse (reaction) turbine?

A

The velocity increases and pressure drops. The direction is what changes

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25
Where does the Impulsive reaction hit the aerofoil on the rotor blade?
On the root
26
Where does the Reaction aspect hit the aerofoil on the rotor blade?
The tip
27
What are rotor blades made out of?
Precision cast
28
Why are turbine blades constructed of a single crystal?
Strong and heat properties
29
What do heat barrier coatings and ceramic/airflow coatings ensure about the turbine?
It is cooler
30
What does a cool turbine ensure about the efficiency of the engine and why?
The exhaust temp is higher increasing efficiency
31
What is the benefit of shrouded turbines?
Vibration resistance Allows lighter stage weights Efficiency
32
Disadvantage of shrouded turbines?
Limits turbine speed so you require more blades
33
What do shrouded turbines form around the perimeter of the turbine rotor?
A band
34
What does the rotor element of a turbine section consist of?
Shaft and a wheel
35
What type of balance is required on a turbine wheel?
Dynamically balancing.
36
What does dynamic balancing consist of?
Blades that have a rotating disc
37
The rotational speeds cause what loads on a turbine?
Centrifugal loads
38
When does a disc become a turbine wheel?
When it has blades attatched
39
What do the blades transmit their energy to?
The rotor shaft
40
How is the disc attached to the shaft?
Bolted or welded
41
What does the disc rim absorb?
Heat from the gases and turbine blades
42
How can you ensure that the disc rim isn't subject to high temperatures?
Bleed cooling air back onto the face of the disc
43
What allows attachment of turbine blades to the disc?
A series of grooves and notches that have the same contour as the blade
44
What compensates for thermal expansion in the attachment of the blade root to the notch?
A clearance
45
What causes the blade root to fit tightly in the disc rim?
Operation of engines and thermal expansion
46
What is the turbine shaft made from?
Alloy steel
47
What are the 2 methods of joining the shaft to the disc?
Bolting and welding (which had a butt or protrusion)
48
What design is common in the attachment of the turbine blades?
Fir tree
49
What must be capable of withstanding torque loads?
Shaft
50
What must the turbine shaft have a means of connection to?
Compressor rotor hub
51
How do you attach the Turbine shaft to Compressor Rotor Hub?
Using spline cuts on the forward end of the shaft
52
What does the spline fit into?
A coupling device
53
What if a coupling device is not used?
Then the turbine shaft may fit into a splined recess
54
Where is a splined coupling method used?
Centrifugal compressor engines
55
What method does axial use?
A splined recess
56
How are the bases retained in their respective grooves?
Peening, welding, lock tabs and riveting
57
Explain the peening method (used frequently)
It requires a small notch to be ground before blade installation After blade is inserted the metal flows into the notch by a small punch mark
58
What does the blade root being made as a stop ensure?
The blade can be removed and inserted in one direction only.
59
When the blade root is being used as a stop, what is on the opposite side of removal and application?
A tang that is bent to secure the blade in the disc.
60
Where are the turbine inlet nozzle guide vanes located?
Aft of the combustion chamber and forward of the turbine wheel
61
Where does the inlet nozzle guide vane experience high temperature?
Aft of the combustion chamber but forwards of the turbine wheel
62
What does the inlet nozzle convert heat and pressure energy to?
Velocity so it can be transferred to mechanical energy
63
How do nozzles convert heat efficiently?
They deflect gasses at a certain angle
64
What is the second purpose of the turbine inlet nozzle? Why?
To direct airflow to the direction of turbine rotation The gas must enter the turbine whilst it is still spinning
65
What does the inlet nozzle assembly consist of?
An inner and an outer shroud
66
Why must the nozzle vanes be contrasted to allow for thermal expansion?
There can be severe warping or distortion otherwise
67
How can you compensate for thermal expansion?
Loose assembly of the shorts (The slots area slightly larger than the vanes)
68
What increases strength rigidity and support in nozzle guide vanes?
Inner and outer support rings
69
What do the support rings also facilitate?
Easy removal of nozzle vanes as a unit (without them, the vanes could fall out as you remove the shroud)
70
What allows for thermal expansion when the vanes are riveted or welded onto the inner and outer shroudes?
The inner and outer shrouds should be cut into segments.
71
Are cracks permitted? How is detection mostly carried out?
No, they need to be replaced Visually
72
What is a structural inspection technique of cracking in a turbine?
Dye penetrant
73
What can be done to pitting raised by FOD?
It can be polished by blending out or stoning
74
What two general equipment can be used to carry out an inspection more efficiently?
Light and magnifying glass
75
How do stress rupture cracks normally appear as?
Hairline cracks that occur on leading/trialing edge at right angles to edge length. (Not less than 1/16)
76
How does deformation caused by overheating appear as?
Wavy
77
On first stage turbine blades, what must you automatically suspect when any stress crack deformation has occurred?
Overheat condition
78
What materials experience creep?
Metals and plastics
79
What is Creep?
A slow deformation on a molecular level caused by prolonged exposure to heat.
80
What promotes creep?
High temperatures
81
What can creep cause concludingly?
Dimensional inconsistency
82
What may scoring identify?
The length of the blade is out of tolerance
83
Why must you number the blades before removal?
To ensure they're put in the correct place that they were taken off of
84
What is another name for the rotor?
Turbine wheel
85
What proceeds first, the nozzle guide vane or the rotor/turbine wheel?
Nozzle guide vane

Module 15 (18 decks)

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