What is the turbine
Transforms a portion of kinetic energy of exhaust gases into mechanical energy to drive the gas generator compressor.
What is the gas generator turbine
Absorbs 60-70% of total pressure energy from exhaust gases. Absorption determined by load the turbine is driving.
Where is the turbine section located
AFT / downstream of combustion
Turbine stage =
Stator ( turbine nozzle guide vane) and rotor
2 types of turbine
Radial and axial flow
What is radial flow
Single stage, used on small GTE
What is axial flow
Used on modern GTE, any number of stages, allows high airflow
Turbine converts
Gas energy from combustion into torque. Impact of gas flow causes turbine to rotate which makes the torque drive turbine shaft.
Impulse turbine
Turbine that rotates from impact of gas flow
Types of turbine blades
Impulse, reaction and reaction-impulse configuration
What is reaction-impulse
Most used, impulse at root, reaction at tip which makes exit pressure constant
What is turbine shaft made from
Alloy steel
Most common method of attaching turbine blades
Fir tree method
How to control temperature on turbine disk
Grooves and notches on rim to allow space for thermal expansion
Stator vanes in slots are…
Slightly smaller than slot to give a loose fit
Cracks on disc require
Replacement of disc and rotor
How do stress rupture cracks appear
Minute hairline cracks on LE and TE at right angles to edge length.
Range from 1/16 length upwards
How does deformation from over temperature appear
Waviness along LE. The LE must be straight and uniform thickness except from areas of blending.
Stress crack or deformation means
Over temperature condition suspected.
What is creep
Slow deformation on a molecule level caused by prolonged exposure to high stresses. Metals and plastics experience.
What promotes creep
Extreme temperatures. Results show dimensional changes.
What does scoring indicate
Length is out of tolerance.
