15.6 Turbines Flashcards
What is the function of the turbine?
To absorb 60-70% of velocity energy and converts it to mechanical energy
What are the two types of turbine?
Radial flow
Axial flow
What are turbines used to drive?
Accessories
Compressors/ fans
What are the characteristics of radial flow turbines?
-always single stage
-only used on small engines such as the APU
-less efficient only able to accept small airflows
What are the characteristics of axial turbines?
-modern engines
-very high airflow
What does the gas pass through before hitting the turbines?
The nozzle guide vane
What is the meaning of an impulse turbine?
Rotation is achieved only by impact on the rotor blades
What are the three classifications of turbine blades?
Impulse configuration
Reaction configuration
Reaction impulse configuration
What is the meaning of reaction turbine?
-fixed nozzle guide vanes are designed to alter gas flow direction without altering pressure
-converging blade passage experience a reaction force resulting from expansion and acceleration of the gas
What is impulse reaction turbine?
-impulse and reaction occurring on the blade
-more common and higher efficiency
-impulse occurs at root remaining blade area is reaction
-AKA reaction
What are the two types of construction for aircraft blades?
Forged
Cast
What casting method provides superior qualities?
Single crystal
What is used to limit heat in turbine blades?
Airflow cooling
Ceramic coating
What does allowing exhaust gasses to be higher in heat allow for?
Increased efficiency in the engine
What is the disadvantage of shrouded turbine blades?
Limits turbine speeds
What is the function of the blade shroud?
Efficiency and vibration improvement
How is the turbine wheel balanced?
Dynamically
What is the turbine disc attached to?
The power transmission shaft
When turbine blades are installed to the disc what does it become?
Turbine wheel
How is the turbine disc protected from hot gasses?
Bleed air is directed onto it
What must the turbine shaft be capable of carrying?
The highest torque loads
What are the methods of attaching disc to shaft?
Welding
Bolting
How is the turbine shaft typically attached to the compressor rotor hub?
Contoured slot
Welded
Riveted
What must turbine blade fittings allow for?
Thermal expansion
What is allowable in terms of turbine blade damage?
-No cracks
-dye penetrant inspection used
-slight damage can be allowed and blended
What is blade creep?
Elongation through force and heat over long periods of time
What are stress rupture cracks?
Minute hairline cracks on the leading and trailing edges
