15.6 TURBINE SECTION Flashcards

1
Q

The gas generator turbine is to absorb approximately —-% of total pressure energy from exhaust gases

A

60-70%

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2
Q

Where is the turbine section of a gas turbine engine located

A
  • Aft
  • directly behind the combustion chamber outlet
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3
Q

What are the 2 different types of turbines on gas turbine engines

A
  • radial flow turbine
  • axial flow turbine
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4
Q

The 2 types of turbine have the same main components which are?

A
  • stationary vanes (turbine nozzle guide vanes)
  • set of moving rotor blades
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5
Q

Explain radial flow turbines

A
  • always single-stage turbines
  • used on small gas turbine engines (e.g. APU)
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6
Q

What are the disadvantages of radial flow turbines

A
  • allow small airflow and less efficient (high aerodynamic losses)
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7
Q

Advantages of radial flow turbines

A
  • simple design
  • easy to manufacture
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8
Q

Explain axial flow turbines

A
  • can be built with any number of turbine stages as necessary
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9
Q

Advantage of axial flow turbines

A
  • allow very high airflow that is required to create high thrust
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10
Q

On modern gas turbine engines, which flow turbine is used

A

Axial

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11
Q

What does the turbine convert

A

Gas energy from combustion chamber into torque to drive turbine shaft

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12
Q

Explain impulse turbine

A

Turbine that makes rotation only by the impact of the gas flow on rotor blades

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13
Q

What are the 3 classification of turbine blades

A
  • Impulse configuration
  • Reaction configuration
  • Reaction-impulse configuration
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14
Q

Explain impulse configuration

A
  • pressure drop across each stage occurs in the fixed nozzle guide vanes (due to convergent shape)
  • increase gas velocity, reducing pressure
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15
Q

Explain reaction configuration

A
  • the fixed nozzle guide vanes are designed to alter the gas flow direction without changing the pressure
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16
Q

Explain reaction-impulse configuration

A
  • used on gas turbine engines
17
Q

Explain shrouded turbine

A
  • limit vibration
  • improves efficiency
18
Q

Disadvantage of shrouded turbine

A
  • limits turbine speed
  • requires more blades
19
Q

How is the turbine wheel balanced

A

Dynamically

20
Q

What 2 things must be controlled to keep turbine operation within operational limits

A
  • engine temperature and speed
21
Q

What does high temperature and high centrifugal loads cause

A

Lower material strength

22
Q

When will the turbine become a ‘turbine wheel’

A
  • when turbine blades are installed onto disc
23
Q

How does the disc rim absorb heat

A
  • from the turbine blades by conduction
24
Q

Why is there clearance between blade root and notch

A

Permit for expansion and contraction of blade

25
What are the 2 methods of connecting a shaft
- weld shaft to the disc - bolting
26
What are the 2 common ways to attach turbine blades
- bulb - Firtree
27
How are the blades retained in their respective grooves
- peening (most common) - welding - lock tabs - riveting
28
What will occur if a crack was found on the disc
- replacement of disc and turbine rotor
29
Explain stress rupture cracks
- appear as minute hairline cracks on or across leading or trailing edge at right angle to the edge length
30
Explain creep
- slow structural deformation - caused by prolonged exposure to high stresses
31
If you remove turbine blades should they be reinstalled in the same slots
Yes
32
Thermal expansion of the turbine nozzles is absorbed by
Loose assembly
33
How is the turbine shaft attached to the compressor rotor hub
Spline - fits into coupling device between turbine and shaft
34
What gives blades better heat and strength properties
Single crystal cast