High speed propulsion employing turbojets, turbofans and variable cycle engines is interpreted here as propulsion for supersonic air vehicles with flight Mach numbers up to the technical limits of the gas turbine. This limit is somewhere between flight Mach numbers of 3 to 4. If the mission asks for higher vehicle speeds then other propulsion concepts need to be considered, eventually in combination with gas turbines dedicated to take off, acceleration and the return segments of the mission. First the thermodynamic cycles of dry and reheated turbojets as well as turbofans are examined at supersonic flight Mach numbers. All point performance calculations are done for altitude/Mach number combinations on a line in the middle of a typical flight envelope with constant equivalent airspeed EAS. For the flight condition of Mach 2 at 11km altitude it is shown that for a given thrust the size of a dry turbofan is significantly bigger than that of an engine with afterburner. However, all the engines must not only be able to operate at their supersonic design condition but also at all the combinations of Mach number and altitude on the flight path from take off to maximum speed. This off-design requirement influences the selection of the aerodynamic compressor design point and consequently also the size of the turbomachines. A short section about variable cycle engines explains with an example how such a machine operates with the various settings of flow diverter valves, mixer and nozzle area. It is shown that in addition to these adjustable geometry elements the core driven fan stage needs variable inlet guide vanes. Finally two components that are not found in engines designed for subsonic flight are described in some detail with examples: the afterburner and the variable area convergent divergent nozzle.


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    Title :

    Mission Defines the Cycle: Turbojet, Turbofan and Variable Cycle Engines for High Speed Propulsion


    Contributors:
    J. Kurzke (author)

    Publication date :

    2010


    Size :

    39 pages


    Type of media :

    Report


    Type of material :

    No indication


    Language :

    English




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