Turbofans and turboprops Flashcards
What is central to the design of the turbofan?
the by-pass ratio
What is the by-pass ratio?
the ratio between the mass flow rate of air drawn in by the fan but bypassing the engine core to the mass flow rate passing through the engine core
What does a high bypass ratio give?
a lower exhaust speed
What does a lower bypass ratio give?
a higher exhaust speed
What is a higher exhaust speed needed to sustain?
supersonic airspeeds
What is a turboprop?
a direct extension of the piston-engine propeller system, where the piston engine is replaced by a gas turbine
What is the purpose of air intake?
*increases pressure by the ram-effect
*ensures uniform flow to the compressor under diverse aircraft incidences
What does air intake not involve?
heat or work exchange with its surroundings
What happens at the air intake?
there is an interchange between kinetic energy and the enthalpy of the gas
this means the flow slows down and the pressure and temperature go up
What is true about compression in subsonic regimes?
compression is realised smoothly
What happens if area increase is abrupt in subsonic regimes?
risk of flow separation
What does the intake of air affect?
the engine performance and the flow around the engine
What problems may arise with military aircrafts?
problems with boundary layer ingestion
What are the main difficulties at supersonic regimes?
the main difficulties arise because of a smooth compression from supersonic to subsonic, which is practically impossible to achieve
What does compression in supersonic regimes almost always involve?
shock waves
