The plug nozzle is a type of nozzle which includes a centerbody or plug around which the working fluid flows. Plug nozzles have applications in aircraft, rockets, and numerous other fluid flows.
Plug nozzles belong to a class of altitude compensating nozzles much like the aerospike which, unlike traditional designs, maintains its efficiency at a wide range of altitudes.
The ideal contour of a plug nozzle is a long tapering 'spike' with a doughnut-shaped combustion chamber situated at the base, hence sometimes this nozzle is also called a "spike nozzle". To save weight, this design is shortened without a large drop in efficiency.
The exhaust is confined by atmospheric pressure so that at different altitudes the varying pressures will allow the exit area to change. This allows perfect atmospheric compensation. With the shortened (or truncated) nozzle, the recirculation of trapped gases at the base of the plug causes a small thrust which offsets the loss due to the non-ideal shape.
Plug nozzles are used in aircraft typically with jet engines both because of the annular shape of the turbine exhaust and for their altitude compensating characteristics. For high speed aircraft, translating the plug or external cowl provides a means of area control with relatively simple actuation. Plug nozzles have been shown to provide noise reduction compared to traditional convergent-divergent nozzles. Weight and cooling are typical concerns with aircraft plug nozzles.
Plug nozzles are used as water nozzles to create a broad spray. The plug can be translated to adjust the area of the passage and thereby adjust the flow rate.
- Aerospike Engine, Jeff Scott, Fall 1999. This paper gives an extensive review of the various altitude compensating nozzle designs.
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