The Turbine Flashcards
Main purpose of the turbine
Extracts energy from the gas stream and converts it to mechanical energy to drive the compressors and engine accessories
Most highly stressed component in the engine
Difference between the HP and LP turbines
LP is located furthest down stream - rotates at a lower speed
HP turbine is located closest to the combustion section - needs to be cooled the most
Why is the turbine located in a divergent duct
To prevent chocking due to back pressure
Purpose of fixed nozzle guide vanes in the turbine section
Direct the gas stream at the right speed and angle to make the turbine move
Relationship between turbine inlet temp and the power to weight ratio
The higher the turbine power inlet, the greater the thermal efficiency and the better power to weight ratio
Blade creep
The high centrifugal and spinning speeds with the added high gas temp causes elongation of the metal beyond its elastic limit
Thats why the blades are under the safe life concept
Turbine blade material
Nickel blades - alloys containing additional elements such as tantalum, aluminium and chromium
Single crystal technology
Internally and externally cooled
Active clearance control (ACC) operation and purpose
Method of controlling turbine blade tip clearance in the turbine casing
Hot bleed air is fed into tubes - causes casing to expand - adjusting this can adjust finely the circumference of the casing
Accessor gearbox purpose and operation
Selection of gears driving other functions - fuel pump, oil pump, hydraulic pump
Starter drives this
What drives the accessory gearbox
Driven from the HP area - the fastest part
