Abstract:
The different aspects of overall performance of three variable cycle engines
(VCE) candidates for future supersonic civil transport are analysed in this work. These
aspects concern the design and off-design points performance, the airframe engine
integration and variable geometry compressor and turbine design and performance.
The three engines are compared to a traditional turbojet. The variable
compressor maps were obtained with their running lines for the whole mission profile
including the transition mode from medium býpass ratio to a lower bypass ratio turbofan.
The specific fuel consumption (SFC) of the VCEs showed a significant improvement,
especially at subsonic cruise, relative to a Turbojet engine. The extent of the variable
geometry on the compressor stator angles, mixing area and the nozzle throat and exit
areas is evaluated. The Fuel bill is estimated for two standard mission profiles.
The effect of installation is estimated on an isolated nacelle. A sizing calculation
is carried out for the whole nacelle including the intake and the nozzle. The drag due to
the friction, pre-entry, afterbody and the shock waves is calculated in order to estimated
the installed performance of the three engines.
In the search of improving the VCE performance at subsonic cruise, the use of
variable geometry at the low pressure turbine for the Turbofan-Turbojet engine is
investigated. The effects of varying the LP turbine guide vanes stagger angle on the
engine performance and component parameters are analysed. The turbine efficiency and
non-dimensional mass flow changes due to the use of variable geometry are estimated.
An updated version of the Turbornatch program was corrected and tested in
order to study variable cycle engines, especially to simulate the transition from one mode
to another.
