Chapter 5: Turbine Flashcards

1
Q

what is the function of turbine?

A

extract energy from gas coming out from combustion chamber to drive compressor and accessories gearbox

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2
Q

what does a turbine stage consist of?

A

1 row of stator & 1 row of rotor

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3
Q

loads on turbine blade

A

1) mechanical forces
2) creep
3) thermo-mechanical fatigue
4) high temp environment
5) oxidation & hot corrosion

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4
Q

what material is used for turbine blade and why?

A

nickel alloy, high specific strength at high temp

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5
Q

what is film cooling?

A

cooling air from compressor that cools external surface

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6
Q

what is impingement cooling?

A

cooling for internal surface

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7
Q

types of turbine blades

A

1) impulse
2) reaction
3) impulse-reaction

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8
Q

what is impulse blade used for?

A

extract high impact energy from gas

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9
Q

pressure and velocity change during impulse blade

A

no change in pressure (straight duct)
velocity deceases

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10
Q

what is reaction blade used for?

A

produce turning forces by aerodynamic action

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11
Q

pressure and velocity change during reaction blade

A

pressure and velocity drop

absolute velocity drops from pushing turbine blades

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12
Q

impulse reaction blade appearance

A

impulse root (c shape), reaction tip (nike tick)

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13
Q

why is impulse reaction blade good?

A

impulse root for high impact power

reaction tip for high speed gas

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14
Q

purpose of nozzle guide vane

A

guide gas from combustor to 1st stage turbine rotor (convergent duct)

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15
Q

definition of primary,secondary, tertiary creep

A

primary: elongation of sample becomes permanent
secondary: no elongation of sample (life of the blade)
tertiary: very fast elongation (fracture occurs instantaneous)

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16
Q

what can creep cause in turbine blades?

A

decrease in blade tip clearance

17
Q

what is turbine case cooling?

A

keep blade tip clearance in check by releasing cold air to shrink turbine casing

18
Q

blade attachment method for turbine blade and why?

A

fir tree (allows thermal expansion to take place)

19
Q

turbine technology

A

1) single crystal blade
2) active clearance control
3) abrasive tip coating
4) bored seals
5) 3D airfoils