Chapter 5: Turbine Flashcards
what is the function of turbine?
extract energy from gas coming out from combustion chamber to drive compressor and accessories gearbox
what does a turbine stage consist of?
1 row of stator & 1 row of rotor
loads on turbine blade
1) mechanical forces
2) creep
3) thermo-mechanical fatigue
4) high temp environment
5) oxidation & hot corrosion
what material is used for turbine blade and why?
nickel alloy, high specific strength at high temp
what is film cooling?
cooling air from compressor that cools external surface
what is impingement cooling?
cooling for internal surface
types of turbine blades
1) impulse
2) reaction
3) impulse-reaction
what is impulse blade used for?
extract high impact energy from gas
pressure and velocity change during impulse blade
no change in pressure (straight duct)
velocity deceases
what is reaction blade used for?
produce turning forces by aerodynamic action
pressure and velocity change during reaction blade
pressure and velocity drop
absolute velocity drops from pushing turbine blades
impulse reaction blade appearance
impulse root (c shape), reaction tip (nike tick)
why is impulse reaction blade good?
impulse root for high impact power
reaction tip for high speed gas
purpose of nozzle guide vane
guide gas from combustor to 1st stage turbine rotor (convergent duct)
definition of primary,secondary, tertiary creep
primary: elongation of sample becomes permanent
secondary: no elongation of sample (life of the blade)
tertiary: very fast elongation (fracture occurs instantaneous)
what can creep cause in turbine blades?
decrease in blade tip clearance
what is turbine case cooling?
keep blade tip clearance in check by releasing cold air to shrink turbine casing
blade attachment method for turbine blade and why?
fir tree (allows thermal expansion to take place)
turbine technology
1) single crystal blade
2) active clearance control
3) abrasive tip coating
4) bored seals
5) 3D airfoils
