15.6 Turbine Section Flashcards
Two types of turbines on gas turbine engines?
Radial flow turbine
Axial flow turbine
The sole purpose of gas generator is to absorb what percent of total pressure energy from exhaust gases?
60-70%
Main components of turbine?
Stationary vanes- named turbine nozzle guide vanes
Set of moving rotor blades
What makes up a turbine stage?
Stator and rotor
How many stages in a radial turbine?
Single staged
Positives of radial turbine
Simple design
Easy to manufacture
Disadvantages of radial turbines?
Only allow small airflows
Less efficient than axial flow turbines
What turbines are used on modern gas turbine engines?
Axial flow tutbines
How many stages in axial flow turbine?
Any number of stages
Advantage of axial flow turbine?
Allows very high airflow to create the high thrust of modern engines
A turbine converts what into what?
Converts gas energy from combustion chamber into torque
The gas flow from combustion chamber first passes through what to reach the turbine?
Stationary turbine nozzle guide vanes
How is the gas flow from the combustion chamber accelerated to the turbine?
Due to convergent shaped ducts between nozzle guide vanes and deflected towards the direction of rotation of the turbine blades
What is an impulse turbine?
A turbine which makes the rotation only by the impact of the gas flow on the rotor blades
Turbine blades are classified by what 3 types?
Impulse configuration
Reaction configuration
Reaction- Impulse configuration
Where is the total pressure drop in an impulse type configuration?
Occurs in the fixed nozzle guide vanes due to their convergent shape, increase gas velocity whilst reducing pressure
In a reaction configuration the fixed nozzle guide vanes are designed to do what?
Alter gas flow direction without changing the pressure
What forces are acting on the blade of a reaction turbine?
Both impulse and reaction forces
Why is ceramic coatings used?
Used with airflow cooling to help keep the turbine blades and inlet nozzles cooler
What do shrouded turbines do?
In effect, form a band around the outer perimeter of the turbine wheel.
Improves efficiency
Permits lighter stage weights
How is the turbine wheel balance?
Dynamically
A method of relieving stresses on disc rim?
Bleed cooling air back onto the face of the disc
What are the grooves for on the rim of the disc?
Allow attachment of turbine blades to the disc
Most common fitting for turbine blades?
Fir tree design
Two basic elements of Turbine assembly?
The stator (Nozzle and inlet guide vanes)
Turbine blades (Rotor)
Where are turbine inlet nozzle vanes found?
Directly aft of combustion chambers
Immediately fwd of turbine wheel
Methods of inspection for turbine?
Visual inspections
Dye penetrant
Is slight pitting allowed on turbine blades?
It may be blended by stoning and polishing. Doesn’t need to be discarded
When any stress cracks are found on the leading edges of the first stage turbine blade what is suspected?
An over temperature condition
