Editing Propelling nozzle (section)

{{short description|Nozzle that converts the internal energy of a working gas into propulsive force}}

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A '''propelling nozzle''' or '''exhaust ejector''' is a [[nozzle]] that converts the internal energy of a working gas into propulsive force; it is the nozzle, which forms a jet, that separates a [[gas turbine]], or [[gas generator]], from a [[jet engine]].

Propelling nozzles accelerate the available gas to [[speed of sound|subsonic]], [[transonic]], or supersonic velocities depending on the power setting of the engine, their internal shape and the pressures at entry to, and exit from, the nozzle. The internal shape may be convergent or [[de Laval nozzle|convergent-divergent]] (C-D). C-D nozzles can accelerate the jet to supersonic velocities within the divergent section, whereas a convergent nozzle cannot accelerate the jet beyond sonic speed.<ref>"Jet Propulsion for Aerospace Applications" second edition, Hesse and Mumford, Pitman Publishing Corporation p136</ref>

Propelling nozzles may have a fixed geometry, or they may have variable geometry to give different exit areas to control the operation of the engine when equipped with an [[afterburner]] or a reheat system. When afterburning engines are equipped with a C-D nozzle the throat area is variable. Nozzles for supersonic flight speeds, at which high nozzle pressure ratios are generated,<ref>"Nozzle Selection and Design Criteria"AIAA 2004-3923, Fig11</ref> also have variable area divergent sections.<ref>"Nozzle Selection and Design Criteria"AIAA 2004-3923</ref> [[Turbofan]] engines may have an additional and separate propelling nozzle which further accelerates the bypass air. 

Propelling nozzles also act as downstream restrictors, the consequences of which constitute an important aspect of engine design.<ref name="Nicholas Cumpsty p144">"Jet Propulsion" Nicholas Cumpsty, {{ISBN|0 521 59674 2}}, p144</ref>