Turbines Flashcards
Function of turbine
Drive compressor and accessory gear box
2 types of turbine
Radial and axial
What type of turbine is most common on modern aircraft
Axial
Advantages of axial turbine
Allows high airflow and creates high thrust , you can use as many stages as necessary
What does the turbine convert
Convert has energy from combustion chamber into torque
Two types of turbines
Impulse and reaction
What turbine does modern aircraft use
Reaction turbine
How can you prevent corrosion of turbine blades
Use correct jet fuel
What is creep
Blades become elongated
What factors effect creep
Material
Temperature
Time
What does the rate of creep depend on
Speed and temperature, if the increase there is more creep
How are HP nozzle guide vanes and rotor blades cooled
Air from engine HPC
What’s the most effect type of cooling
Film Cooling
How is plastic deformation limited
Efficient cooling of turbine materials
What’s a negative of film cooling
Small holes are difficult to make and expensive
Why is film cooling most effective
Maximum cooling effect with minimum cooling air which allows more air used to drive turbine
How are nozzle guide vanes cooled in the second sage
Convection and impignet
How are second stage rotor blades cooled
Convection only
Two types of clearance control
Passive and active
Where is passive used
HP & LP Turbines
What’s the LP turbine cooling source
Fan air
What’s an advantage of tip clearance control
Saves a lot of fuel
How is clearance control valves controlled
Controlled by ECU and actuated by fuel pressure from hydro-mechanical unit
When does active clearance control work
During climb and cruise
When is active tip clearance most effective
When engine operates at high power for a long time
At cruise how much of n2 is used
80-95%
clearance control valve controlled with what motor
Torque motor
What’s the parts of a Turbine construction
HPT , LPT , Turbine Frame
Where is the turbine frame located
Behind low pressure turbine
What loads do the turbine frame carry
Bearing loads of the aft end of LPT
Transmits loads to rear engine mount on turbine frame
How is the HPT case made
In one piece
How are nozzle guide vanes in the HPT made
Vane segments with each segment having usually 2 nozzle guide vanes
Where is the inner seal located
Inner surface of nozzle guide vane segments
Components of a HPT Rotor
Turbine disc
Rotor blade
rotating interstate seal
Fwd and rear blade retainers
What’s an interstate seal
Acts as a spacer between 2 discs
How are turbine blades held in place
Blade retainers
What are the retainers in LP turbines
Strip type which fit into dovetail slots and are bent up at each end
Rotor blade in HPT shape
Fir tree root
Benefit of fir tree root design
Many contact surfaces
What are the turbine blades used in rotor assembly
Open end and shrouded
When are open end turbine blades used
Turbines with high rotational speeds
How is the added weight in an shrouded blade in a LPT offset
Thinner blades which make it more efficient
How are turbine discs installed
Directly splined or bolted
How are HPT Blades cooled
Internal cooled by air form HPC
What’s an aft major structural component
Turbine Frame
What does the turbine frame support
1 or 2 turbine rotors & provides attachment points for the rear engine mount
How big should a radial strut be
As short as possible to minimise expansion which keeps stress on frame hub low
Tangengal struts minimise what
stress caused by thermal expansion
