Gas turbine principles Flashcards
What is the brayton cycle
Compression,combustion,
expansion, exhaust.
All occur continuously and at the same time.
What does the convergent duct of the exhaust pipe do.
Called a jet nozzle. Increases the speed of gas flow exiting the engine.
What is the thrust formula
Thrust=Mx(VJET-VFLIGHT) where Vflight is speed of air entering and Vjet is speed of jet exhaust.
What is pressure thrust
An additional source of thrust. Achieved by choking the exhaust. Raises static pressure at exhaust exit and difference between ambient static pressure generates an unbalanced force.
What is axial flow
Flow along longitudinal axis of the engine from front to rear. Only mass flow that generates thrust.
What is tangential flow
Flow around engines axis parallel to its circumference. Causes a reactive torque force but contributes nothing to thrust.
What do flow straighteners do
In bypass duct and in exhaust. Try to eliminate as much tangential flow and convert it to axial flow.
What happens in the compressor
Pressure increases as air travels rearwards. To ensure flow unit is contained within a convergent duct.
Where does the area of highest pressure exist
Diffuser is area of highest pressure. Divergent duct exists between compression and combustion.
What happens in the combustor
Combustion is continuous. Pressure is lower Than pressure of air exiting diffuser to ensure flow does not go back the other way. Exit is convergent gas velocity increases.
What factors affect thrust
Altitude,speed, ambient temp, engine bleed, intake heating
What is engine bleed
Air taken from engine to power other aircraft systems reducing mass flow thus reducing thrust.
What is intake heating
Intake heating systems reduce air density and so reduce mass flow.
When is maximum thrust produced.
When aircraft is stationary on ground. Difference between vjet and vflight is greatest. Unit for thrust force is N or LB
What is flat rating
On V.cold days engine may produce more thrust that airframe can safely take. Engines have their maximum thrust limited by controlling fuel flow to engine. Known as flat rating
