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M15 > 15.6 Turbine Section > Flashcards

15.6 Turbine Section Flashcards

1
Q

What does the turbine section do?

A

Transforms kinetic energy to mechanical energy to drive the compressor and accessories.

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2
Q

What is the purpose of a gas generator turbine?

A

To absorb 60 to 70% of total pressure energy.

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3
Q

What are the 2 types of turbines used?

A

Radial flow and axial flow.

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4
Q

What can be said about the stages of a radial flow turbine?

A

Always only single stage.

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5
Q

Where is a radial flow turbine used?

A

On APUs.

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6
Q

What are the negatives of a radial flow turbine?

A

Small airflow.
Less efficient.

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7
Q

Where are axial flow turbines used?

A

On modern engines.

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8
Q

What is the advantage of the axial flow turbine?

A

Allows very high airflow to create high thrust.

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9
Q

What does a stage consist of in the turbine?

A

Nozzle guide vane (stator), then a rotor.

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10
Q

What effect do nozzle guide vanes in the turbine have on velocity and pressure?

A

V increases.
P decreases.

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11
Q

What effect do rotors in the turbine in the turbine heave on velocity and pressure?

A

V decreases.
P increase.

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12
Q

How do turbine blades operate.

A

Converts gas energy (convergent shaped) from the combustion chamber into torque.
Impact of gas flow on the blades rotates the turbine.

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13
Q

What is key about how an impulse turbine operates?

A

The turbine only rotates from gas flow impact on the rotor blades.

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14
Q

What are the 3 configurations of turbine rotor blades?

A

Impulse.
Reaction.
Reaction - impulse.

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15
Q

What is key about the fixed nozzle guide vanes in an impulse configuration and why ?

A

Due to their convergent shape, It is where the total pressure drop occurs at each stage.

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16
Q

Describe the total pressure drop of an impulse turbine blade configuration?

A

It is too big.

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17
Q

What does an impulse turbine blade configuration do to energy?

A

Converts all static pressure energy to kinetic energy.

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18
Q

What do fixed nozzle guide vanes do in a pure reaction turbine blade configuration?

A

They alter gas flow direction without changing pressure.

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19
Q

Describe the pressure drop of a pure reaction turbine blade configuration?

A

It is too little.

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20
Q

What turbine blade configuration is normally used?

A

Reaction- impulse.
Known as a reaction turbine.

21
Q

Where does impulse force act in a reaction turbine blade configuration.

A

At the roots.

22
Q

Where does reactions force act on a reaction turbine blade configuration?

A

At the tip.

23
Q

How are turbine blades constructed?

A

They are precision cast as a single crystal.

24
Q

Why are the turbine blades single crystal?

A

Provides better strength and heat properties.

25
Q

What is done to turbine blades to keep them and the inlet nozzles cooler?

A

A ceramic coating is added.

26
Q

What does a ceramic coating on turbine blades allow for ?

A

A higher exhaust temperature, increasing the efficiency of the engine.

27
Q

Where are shrouded turbine blades used?

A

On low pressure turbines.

28
Q

What is the advantage of shrouded turbine blades?

A

Increased efficiency and vibration characteristics resulting in lighter stage weight.

29
Q

What is the purpose of the holes in turbine blades?

A

Purely for cooling.

30
Q

Define a turbine wheel.

A

A dynamically balanced unit of blades attached to a rotating disc.

31
Q

What is the turbine disc attached to ?

A

To the main transmitting shaft.

32
Q

What is the most common attachment for turbine blades?

A

Fir tree.

33
Q

What relieves stresses from hot gasses on the disc rim?

A

Bleeding cool air.

34
Q

What can be found on the rim of the turbine disc ?

A

Grooves for blade attachment.

35
Q

The turbine shaft must be capable of absorbing high torque loads. How is this achieved?

A

Welding the shaft to the disc.
Bolting.

36
Q

What is the purpose of a spine cut on the fwd end of the shaft?

A

Attachment for the shaft to the compressor rotor hub.

37
Q

Where is a splined coupling arrangement used?

A

On centrifugal compressor engines.

38
Q

What’s the most common method to retain turbine blades in grooves?

A

Peening.

39
Q

What is peening?

A

The blade is installed then the notch is filled by the disc metal.

40
Q

What is another method of blade retention?

A

Using the blade root as a stop and the other end has a tang bent to secure the blade in the disc.

41
Q

Where are nozzle guide vanes located in a turbine?

A

Aft of the combustion chamber.

42
Q

What is the primary purpose of the nozzle guide vanes?

A

To convert heat and pressure to velocity energy.

43
Q

What is the secondary purpose of the nozzle guide vanes?

A

Deflect gasses to a specific angle.

44
Q

How are nozzle guide vanes assembled?

A

Between inner and outer shrouds/rings.
Each vane fits into a contoured slot in the shrouds.

45
Q

How are turbine blades inspected for stress and creep?

A

Mainly visually.
Or dye penetrant.

46
Q

What can cause stress rupture cracks?

A

Overtemprature conditions.

47
Q

What is creep on turbine blades?

A

Slow structural deformation on a molecular level due to prolonged exposure to high stresses.

48
Q

What makes creep on turbine blades worse?

A

High temperatures.

49
Q

How big are turbine cracks types?

A

1/16 of an inch or bigger.

M15 (18 decks)

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