15.6 Turbine Section Flashcards
(30 cards)
What does the gas generator do?
Absorbs 60-70% of the total pressure energy from exhaust gases
What does the turbine section do?
Transforms a portion of kinetic (velocity) energy of exhaust gases into mechanical energy to drive the gas generator compressor and accessories
What are the 2 types of turbines on GTEs?
Radial flow and axial flow
What does a turbine stage consist of?
Stator then rotor
How many stages does an axial flow turbine have?
Unlimited
How many stages does a radial flow turbine have?
1
What type of engines are radial flow turbines used on?
Small GTEs (APU)
What type of engines are axial flow turbines used on?
Modern GTEs
Does a radial flow or axial flow turbine permit high airflows?
Axial flow
How is the gas flow from the combustion chamber accelerated?
NGVs have convergent shaped ducts in between them
What are the 3 types of turbine blades?
Impulse, reaction and impulse reaction
What does the rotor element of a turbine section consist of?
Shaft and wheel
What 2 things does a turbine wheel consist of?
Disc and blades
How are the disc rim thermal stresses decreased?
By bleeding cooling air back into face of the disc
How does the turbine disc rim absorb heat from the turbine blades?
By conduction
What is a turbine shaft fabricated by?
Alloy steel
What method is used to attach turbine blades?
Fir tree design
What are the 3 methods of connecting the shaft to the turbine disc?
Welding, bolting and splined coupling
What type of engine uses splined couplings?
Centrifugal compressor engines
What are the 4 methods of retaining blades?
Peening, welding, lock tabs and riveting
Are cracks usually permitted on turbine blades?
No
What do the NGVs do on an impulse turbine?
Increase gas velocity whilst decreasing pressure
What do NGVs do on a reaction turbine?
Alter gas flow direction without changing pressure
What part of the blade is reaction and impulse on an impulse-reaction turbine?
Impulse at root, reaction at tip
