Module 15.6 Turbine section Flashcards
What is the sole purpose of the gas generator turbine?
Absorb 60-70% of the total pressure energy
The turbine turns KE into what?
Mechanical energy
What are the two types of turbine?
- Radial flow
- Axial flow
How many stages are radial turbines?
One
What is an advantage of axial turbines?
Very high airflow
What is one compressor stage?
Rotor then stator
What is one turbine stage?
Stator then rotor
Which turbine makes rotation only by the impact of the gas flow on the rotor blades?
Impulse turbine
What are the 3 types of turbine blades?
- Impulse configuration (called pure impulse)
- Reaction configuration (called pure reaction)
- Impulse-reaction configuration (commonly called reaction type)
In the impulse configuration, what is the total pressure drop across?
Nozzle Guide Vane (NGV)
Kinetic energy increases
What shape are the fixed NVG’s?
Convergent
In the reaction type configuration, what are the fixed NVG’s designed to do?
Alter gas flow direction without changing the pressure
What forces act on the blade of a reaction turbine?
Impulse and reaction
Where do the impulse forces act on the reaction turbine?
At the blade root
Where do the reaction forces act on the reaction turbine?
At the blade tip
In the impulse configuration, what increases across the NGV’s?
The gas velocity
Better strength and heat properties are obtained by casting blades as?
Single crystal
What is used to cool nozzles and turbine blades?
- Ceramic coating
- Airflow cooling
What type of turbine blades improve efficiency and vibration and permit lighter stage weights?
Shrouded turbine blades
What is the disadvantage to shrouded turbine blades?
Limits the turbine speed
Why is the shrouded turbine rpm limited?
As there is a higher moment weight
Where should shrouded turbine blades be used?
Low pressure turbine as it spins slower
Where can’t shrouded turbine blades be used?
High pressure turbine
What are the turbine blades installed on to?
Turbine disc
