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M15 New > 15.6 > Flashcards

15.6 Flashcards

1
Q

What does the turbine transform

A

Part of the kinetic (velocity) energy of exhaust gases into mechanical energy to drive gas generator compressors and accessories

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2
Q

Purpose of gas generator turbine

A

Absorb 60-70% of total pressure energy from the exhaust gases

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3
Q

Where is the turbine located

A

Aft or downstream of the combustion chamber

Directly behind gas chamber outlet

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4
Q

Turbine main components

A

Stationary vanes - turbine nozzle guide vanes

Rotor blades on a turbine disk

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5
Q

Radial flow stage ?

A

Single stage used on APU

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6
Q

Radial flow disadvantage

A

Small airflows and less efficient due to high aerodynamic losses

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7
Q

Where are axial flow turbines used

A

Modern GTE

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8
Q

Advantage of axial flow turbine

A

Very high airflow required to create a high thrust

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9
Q

Turbine stage

A

Stator and rotor

(Stator first)

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10
Q

How many stages can an axial flow turbine have

A

Any number of

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11
Q

What does the turbine convert

A

Gas energy from combustion chamber into torque

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12
Q

After the combustion chamber what’s the first part the gas flows through

A

Stationary turbine nozzle guide vanes Rotor blades

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13
Q

How is the gas flow in the combustion chamber accelerated

A

Convergent shape duct between nozzle guide vanes Rotor blades

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14
Q

What is an impulse turbine

A

Turbine that only rotates due to impact of gas flow

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15
Q

3 types of turbine blade

A

Impulse

Reaction

Reaction - impulse

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16
Q

In an impulse turbine where does the total pressure drop occur

A

Fixed nozzle guide vanes because of their convergent shape

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17
Q

In a impulse configuration what is pressure energy converted to

A

All pressure energy converted into kinetic energy

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18
Q

What is a reaction type configuration designed to do

A

Alter gas flow direction without changing the pressure

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19
Q

What turbine combination do GTE use

A

Reaction - impulse

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20
Q

What forces are acting on a reaction turbine

A

Both impulse and reaction forces that acts in the plane of rotation to drive the turbine

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21
Q

What do impulse turbines require

A

High - velocity gas to obtain the maximum rate of momentum change

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22
Q

How does a reaction turbine cause its rate of momentum to change

A

By nozzling action of the rotor blade

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23
Q

What does a uneven workload cause if the blade

A

Gases to exit from the blade at different velocities and pressures

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24
Q

What type of cast are most blades

A

Precision

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25
Q

Why do we cast as single crystal

A

Gives blades better strength and heat properties

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26
Q

How do we keep turbine blades and inlet nozzles cooler

A

Using heat barrier coatings like ceramic coatings

Airflow cooling

27
Q

What effect does keeping inlet nozzles cooler have

A

Increase efficiency of the engine

28
Q

Advantage of shrouded turbine blades

A

Improves efficiency and vibration characteristics

Lighter stage weights

29
Q

Disadvantage of shrouded turbine blades

A

Limits turbine speed and requires more blades

30
Q

Why do we need additional turbine stages

A

Single turbine wheel cannot absorb enough power from exhaust gases to drive the components

31
Q

What does the rotor element of a turbine section consist of

A

Shaft and wheel

32
Q

Why do we control engine speed and temperature

A

To keep turbine within operations limits due to high centrifugal loads and temperatures on it

33
Q

How is a turbine wheel balanced

A

Dynamically

34
Q

What is the disc attached to

A

Main power-transmitting shaft of the engine

35
Q

What is the purpose of grooves/notches in the rim of the disk

A

Allow attachment of the turbine blades and space for thermal expansion

36
Q

What material is turbine shaft

A

Alloy steel that can absorb high torque loads

37
Q

How do you cool the disk rim

A

Bleeding cooling air back onto the face of the disk

38
Q

Most common method of connecting shaft to turbine disk

A

Bolting

39
Q

How is the turbine shaft attached to compressor rotor hub

A

Spline cut on the forward end of the shaft

40
Q

What does a spline it into

A

Coupling device between compressor and turbine shafts

41
Q

What do we use if a coupling is not used

A

Splined end of the turbine shaft may fit into a splined recess in the compressor rotor hub

42
Q

Where is the splined coupling arrangement used

A

Centrifugal compressor engines

43
Q

Most common way to attach turbine blades

A

Fir tree design

44
Q

Methods of retaining blades

A

Peening , welding , lock tabs and riveting

45
Q

What is a notch filled with

A

Disc material

46
Q

Why is the tang bent

A

Secure blade in the disc

47
Q

What does using the Blade root as a stop do

A

Made on one end so the blade can only be inserted and removed in one direction

48
Q

2 parts of turbine assembly

A

Stator - nozzle and inlet guide vanes

Turbine blades (rotor)

49
Q

Stator 3 different names

A

Turbine inlet nozzle vanes

Turbine inlet guide vanes

Nozzle diaphragm

50
Q

Where is the turbine inlet nozzle vane located

A

Aft of the combustion chambers and immediately forward of the turbine wheel

51
Q

Where are turbine inlet nozzle assembled

A

Between outer and inner shrouds on rings

52
Q

Where do vanes fit

A

Contoured slot in the shrouds

53
Q

How can we fit vanes into inner and outer shrouds

A

Weld or river them into position

54
Q

Why is the shroud ring cut into segments

A

To allow for thermal expansion

55
Q

What’s a structural inspection technique

A

Dye penetrant

56
Q

How can we get rid of putting in blades

A

Stoning and polishing

57
Q

How do stress rupture cracks from

A

At aright angle to the edge length

58
Q

How does deformation due to over temperature appear

A

Waviness

59
Q

Length of visible cracks

A

1/16th inch upwards

60
Q

What happens if cracks or deformation occurs on the leading edge of the first stage turbine blade

A

Over temperature condition must be suspected

61
Q

What is creep

A

Slow structural deformation on a molecular level

62
Q

How does creep occur

A

Prolog exposure to high stresses and high temperatures

63
Q

What does scoring on the turbine case suggest

A

Length of blades out of tolerance

M15 New (18 decks)

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