Turbines Flashcards
What does the turbine drive and how does it do it?
Drives the compressors, Power Shaft, and Accessories
By extracting energy from the hot gases released from combustion and expanding them to a lower temperature and pressure
Application of the Multi-stage turbine is to?
Drive the multi-stage compressors
Drive the power shafts
Driving fans
Describe the Turbine Passages?
Aerofoil shape rotors and stators
Rotorsand the stators are converging nozzle guide vanes
The stator is followed by the turbine rotor
What is the purpose of Nozzle Guide Vanes
It is a fixed blade to achieve a significant pressure drop and velocity increase. Turns the Gas path from axial to the direction of rotation and directs the gasses onto the turbine rotor at the optimum angle of attack.
What could it mean if the exit of nozzle guide vanes are too open or too closed?
Open: There is less kinetic energy created so the gas path has less energy impinging on the turbine blades.
Closed: The engine could choke up and a surge may occur.
What do impulse blades do?
Change in flow direction with little pressure and speed change. This change in direction causes the turbine blade to rotate.
What do reaction blades do?
Presents a reduction in pressure and increase in velocity, this is achieved by creating a convergent duct between the blades.
What is the design of impulse and reaction blades?
Near pure impulse at the root and gradually change to a reaction design closer to the tip. (Blade Twist)
Why is blade twist important?
The turbine blades at the root and tip are traveling at different speeds, so this design is able to maintain a high level of blade efficiency as the speed increase from the root to the tip.
How much gas path energy flowing across the turbine does the compressor use?
75%
As the gas path travels through the turbine assembly it loses energy, how is the energy recovered?
The diverging turbine assembly and increasing blade length.
What is the advantage of ceramic coating blades?
Increase heat resistance
What are the advantages and disadvantages of tip shrouds?
Tip shrouds prevent efficiency from being lost with gasses escaping over the tip of the blade
Disadvantage: Blade weight increase which increases the creep potential
What is the function of the case?
To contain the turbine section, gas stream and support the nozzle guide vanes
What is the function of the shaft?
To connect the/drive the compressor section
