26-07-2012, 10:49 AM
Turbine Blades
Turbine_Blades.ppt (Size: 592.5 KB / Downloads: 118)
Design Considerations
Geometry
Cooling Vanes
Attachment Interface
Safety Factors
Geometry
Strength / Fatigue Life
Each row will be different
Air Flow (CFD Package)
Machineability
Cooling Vanes
Blades must be kept cool
Often operate near the metal melting point
An increase of only 17 C can decrease the engine life by half
Cool (300 C ) air is run out of the blades through small holes (vanes), keeping the blades from melting.
Attachment
Keep Stress Concentrations Low
“Fir Tree” Attachment
Reduced stress
concentrations
Easy replacement
Also known as the
“Christmas Tree”
Safety Factors
Higher S.F. is usually the best.
But what if the engine runs out of control at speeds higher than intended?
The energy of the rotating blades goes up with ω2
What happens if the blades brake at 10% overload? 20%, 30%, 40%, 50% ?
Too much energy and the blades might break through the engine shroud and into the fuselage.
Environment
Air Temperature: Between 850 and 1600 °C
Melting Temperature:
Steel:1400C
Nickel Alloy: 1200C
Titanium:1650C
Turbine RPM: Appx. 20,000 rpm
Creep
Turbine blades elongate during their life
Tip clearance
Result of environment and grain structure
Soft “abradable” lining
Directional solidification (cooling)
Single crystal structure