M15.6 Flashcards
What does the turbine provide power to?
The compressors and accessory gearbox
Where do turbines extract energy from?
The hot gases from the combustion chamber
What are the two types of turbines on gas turbine engines?
- radial flow (turns air 90)
- axial flow (air stays straight)
What are the turbine stationary vanes also called?
Turbine nozzle guide vanes
What does one stage consist of?
A stator and rotor
How many stages does a radial flow turbine have?
Always one
Where are radial flow turbines used?
On small gas turbines such as APU
How many stages does an axial flow turbine have?
As many that is necessary for the job
What does the turbine convert the gas energy from the combustion chamber into?
Torque
What is the impulse-reaction turbine often called?
A reaction turbine
What must turbine materials be able to withstand?
Extremely high temperatures and very high centrifugal forces
How does corrosion from sulphuric acid occur?
Because of sulphur in fuel and high gas temperatures
How is corrosion from sulphuric acid prevented?
By the correct use of fuel
When would material deformation known as creep occur?
maximum engine power (When high centrifugal forces are applied over a long period of time with high temperatures)
When creep happens does the material return back to its original shape?
No
How can plastic deformation be limited?
By efficient cooling
How does convection cooling work?
It puts cold air inside of the material to cool it down
Where is convection cooling used?
Turbine nozzle guide vanes and turbine rotor blades
What cooling method is the easiest?
Convection cooling
How does impingement cooling work?
An insert is placed inside the blade and uses small holes to spray the inside of the blade
How does film cooling work?
It uses air holes to put a cold film around the blade
What type of turbine cooling method is the most efficient?
Film cooling
What are the first stage nozzle guide vanes cooled by?
- convection
- impingement
- film cooling
What are the first stage rotor blades cooled by?
- convection
- impingement
- film cooling
What is the second stage nozzle guide vanes cooled by?
- convection
- impingement
What is the second stage rotor blades cooled by?
-convection
Why is using multiple cooling types a benefit?
Because its a good balance f costs, efficiency, and service life
What is tip clearance?
The gap between the blade tip and casing
If there is no clearance control system how much does fuel consumption increase by?
Four times higher than if there was one
What is active clearance control system?
It’s a system that keeps the tip clearance as small as possible in all operating conditions
What are spray rings?
They’re rings that go around the turbine cases to cool them down
How do spray rings work?
They work by spraying air through tiny holes
What shape are the spray rings on the low pressure turbines?
Circular
What shape are the spray rings on the high pressure turbines?
Rectangular
What is the job of a interstate seal?
To prevent gas flow trough the gap between the stator and the rotor
What a re blade retainers designed to do?
Hold the blades in place so that they do not move
Rotor blades on the high pressure turbine have special shaped roots, what are these called?
Fir tree root
Why are fir tree roots used?
So forces can be transmitted smoothly which increases longer service life
What are the two main types of turbine blades used today?
Open end blades and shrouded blades
Where are open end turbine blades used?
High rotational speeds and high pressure turbines
Where are shrouded turbine blades used?
Low pressure turbines and lower rotational speeds
Why are shrouded blades used?
Because they reduce vibration by forming a band at the blade tips
Where are the high pressure turbine blades cooled from?
They’re called internally from the high pressure compressor
Why are the turbine frame struts hollow?
Gives room for oil supply lines, scavenge lines, oil drain lines
What are the two types of turbine frame struts?
Radial struts and tangential struts
Why are turbine frames with the radial struts designed as short as possible?
It minimises the expansion of the struts and keeps stress low
Why would tangential struts be used on a turbine frame?
It minimises stress because if they expanded it will caused it to rotate slightly
