Turbine Engine Turbine Section Flashcards
What is the function of a turbine nozzle guide vane assembly (nozzle diaphragm) ?
To accelerate the gas flow and to guide it onto the first stage turbine blades at the optimum angle.
Why does the diameter of the turbine discs increase progressively through the various stages?
To extract the maximum energy out of the gas stream as its energy reduces by the expansion through the earlier turbine stages.
What type of turbine blades are generally used in modern turbine engines?
Modern turbine engines utilise combined impulse/reaction blades.
Why is there a limit to the maximum gas temperature?
To overheat damage to the turbine section, primarily the nozzle guide vanes and the first stage turbines.
Which part of a turbine engine is most likely to sustain damage as the result of a hot start?
The nozzle guide vanes and first stage turbine.
What factor limits the output of the turbine section?
The temperature bearing capacity of the nozzle guide vanes.
How are turbine section components cooled?
By passing relatively cooler air over and or through them.
How does the pressure, velocity and temperature of the gas change as it passes through the turbine section?
Pressure progressively reduces. Velocity increases significantly through the nozzle guide vanes and fluctuates on a reducing trend through the turbine stages but is increased overall. Temperature progressively reduces.
What are the purpose of adding a shroud to the tips of some turbine blades?
To prevent gas leakage past the blade tips.
To increase rigidity and reduce vibration.
What is turbine creep?
To gradual, progressive and permanent lengthening ( elongation) of turbine blades.
What causes creep?
Creep is caused the combined effects of temperature and centrifugal stresses.
What is tertiary creep?
The final stage of creep development before turbine blade failure, where it is potentially detrimental to continue to operate the engine.
