Chap - 2 Turbines Flashcards
Purpose of a turbine
Extract sufficient energy from the gas stream to drive the compressor and the accessories
Provides shaft power for a propeller or rotor
The turbine turns gas energy into what
Mechanical energy
Turbine consists of three main parts
Nozzle guide vanes
Rotating turbine disc
Turbine blades
Nozzle guide vanes
Aerofoil shapes
Forming convergent duct
Nickel alloy
Usually hollow
Cooled by compresdo4 delivery pressure
Turbine disc
Nickel based alloy
Machine forged with integral shaftbor with flange
Cooling air is passed across both faces of the disc - limits heat from turbine blades
Fir tree root
Blade is free in serrations when the turbine is stationary and is stiffened by centrifugal force when turbine is rotating
BLISK
Method of resisting high stresses imposed on blade root
Blades permanently attached to the disk
Turbine blades must be designed to resist
Fatigue
Thermal shock
Corrosion
Oxidiazation
High temp
Centrifugal force
High rotational speeds
High frequency gas flows
Blade creep
Turbine blades slowly grow in length
Blade creep is due to 3 factors
Centrifugal force
High temperature
Running hours
Crep is likely to occur in the following time periods
Primary - new engine
Secondary - normal service use
Tertiary - excess temp and running hours
Blade development
Encourages the metal to grow into one single crystal during casting
Encourages the metal to grow into one single crystal during casting
What does this do
Improves temp resistance
Better creep resistance
Longer life
How do you obtain max efficency and performance of the engine
Compressor and turbines are matched
Maintenance of turbines
Turbine tip clearance check (creep)
Bearing wear/failure
Run down check- within limits
Overheating check
FOD damage on:
A. compressor
B. Turbine
C. Exhaust
Corrosion/erosion- prevented by compressor washing
