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CAA Module 15 > Module 15.6 Turbine section > Flashcards

Module 15.6 Turbine section Flashcards

1
Q

What is the sole purpose of the gas generator turbine?

A

Absorb 60-70% of the total pressure energy

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2
Q

The turbine turns KE into what?

A

Mechanical energy

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3
Q

What are the two types of turbine?

A
  • Radial flow
  • Axial flow
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4
Q

How many stages are radial turbines?

A

One

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5
Q

What is an advantage of axial turbines?

A

Very high airflow

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6
Q

What is one compressor stage?

A

Rotor then stator

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7
Q

What is one turbine stage?

A

Stator then rotor

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8
Q

Which turbine makes rotation only by the impact of the gas flow on the rotor blades?

A

Impulse turbine

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9
Q

What are the 3 types of turbine blades?

A
  • Impulse configuration (called pure impulse)
  • Reaction configuration (called pure reaction)
  • Impulse-reaction configuration (commonly called reaction type)
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10
Q

In the impulse configuration, what is the total pressure drop across?

A

Nozzle Guide Vane (NGV)

Kinetic energy increases

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11
Q

What shape are the fixed NVG’s?

A

Convergent

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12
Q

In the reaction type configuration, what are the fixed NVG’s designed to do?

A

Alter gas flow direction without changing the pressure

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13
Q

What forces act on the blade of a reaction turbine?

A

Impulse and reaction

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14
Q

Where do the impulse forces act on the reaction turbine?

A

At the blade root

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15
Q

Where do the reaction forces act on the reaction turbine?

A

At the blade tip

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16
Q

In the impulse configuration, what increases across the NGV’s?

A

The gas velocity

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17
Q

Better strength and heat properties are obtained by casting blades as?

A

Single crystal

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18
Q

What is used to cool nozzles and turbine blades?

A
  • Ceramic coating
  • Airflow cooling
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19
Q

What type of turbine blades improve efficiency and vibration and permit lighter stage weights?

A

Shrouded turbine blades

20
Q

What is the disadvantage to shrouded turbine blades?

A

Limits the turbine speed

21
Q

Why is the shrouded turbine rpm limited?

A

As there is a higher moment weight

22
Q

Where should shrouded turbine blades be used?

A

Low pressure turbine as it spins slower

23
Q

Where can’t shrouded turbine blades be used?

A

High pressure turbine

24
Q

What are the turbine blades installed on to?

A

Turbine disc

25
Q

What is the turbine disc attached to?

A

Main power transmitting shaft

26
Q

What is it called when the blades are installed on the turbine disc?

A

Turbine wheel

27
Q

What balance type is a turbine wheel?

A

Dynamically

28
Q

What is one method of relieving stresses on the disc rim?

A

Bleed cooling air on the face of the disc

29
Q

What are the two methods of connecting the shaft to the disc?

A
  • Welding
  • Bolting
30
Q

What allows the shaft to spin the compressor?

A

Splines cut into forward end of the shaft

31
Q

What do the turbine shaft splines fit into?

A
  • Coupling device
  • Recess in compressor rotor hub
32
Q

What compressor shaft connection do centrifugal compressors use?

A

Coupling device

33
Q

What are the two types of blade to disc attachments?

A
  • Bulb
  • Firtree
34
Q

What are the methods of retaining the fan blades into the disc?

A
  • Peening
  • Welding
  • Lock tabs
  • Riveting
35
Q

What is the purpose of the NGV?

A
  • Straighten and guide gas flow
  • Decrease static pressure
  • Increase velocity
36
Q

What comes after the first NGV’s in the blade section?

A

Rotor, High pressure turbine

37
Q

What are the NGV’s fitted between?

A

The outer and inner shrouds/rings

38
Q

What fit do the slots give the vane?

A

Loose fit

39
Q

What are the 3 methods of fitting vanes into the shrouds?

A
  • Riveting
  • Welding
  • Contoured slot
40
Q

What does the fit of the vanes allow for?

A

Thermal expansion

41
Q

How is inspection for cracks conducted?

A

Mainly visual, but some structural techniques like dye penetrant may be used

42
Q

What damage may be blended by stoning or polishing?

A

Pitting

Cracks cause replacement

43
Q

What is blade creep?

A

Elongation of the blade by the centrifugal forces and temperature

44
Q

When stress cracks or deformation are found on the LE of 1st stage turbine blades, what is suspected?

A

Over temperature condition

45
Q

How do stress cracks appear visually?

A

Hairline cracks at right angles to edge length

CAA Module 15 (18 decks)

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