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In aeronautics, a ducted fan is a thrust-generating mechanical fan or propeller mounted within a cylindrical duct or shroud. Other terms include ducted propeller or shrouded propeller . [ 1 ] When used in vertical takeoff and landing ( VTOL ) applications it is also known as a shrouded rotor .
In October 2013, the European Commission gave a three-and-a-half-year grant to study the Innovative Counter rOtating fan system for high Bypass Ratio Aircraft engine (COBRA). COBRA was a European Union-Russia cooperative program to study an ultra-high bypass ratio (UHBR) counter-rotating turbofan (CRTF) that was similar to the NK-93.
The propulsive efficiency is always less than one, because conservation of momentum requires that the exhaust have some of the kinetic energy, and the propulsive mechanism (whether propeller, jet exhaust, or ducted fan) is never perfectly efficient. It is greatly dependent on exhaust expulsion velocity and airspeed.
All practical airbreathing jet engines heat the air by burning fuel. [1] Alternatively a heat exchanger may be used, as in a nuclear-powered jet engine. [6] Most modern jet engines are turbofans, which are more fuel efficient than turbojets because the thrust supplied by the gas turbine is augmented by bypass air passing through a ducted fan. [4]
One of the key reasons for using a ducted fan is its ability to increase Reynolds number within the duct, thus to increase the rotational speed before the tip speed becomes supersonic (a typical hard limit on propeller performance - propellers don't operate well with supersonic tips). Yet neither of these are mentioned in the article.
A centrifugal fan is a mechanical device for moving air or other gases in a direction at an angle to the incoming fluid. Centrifugal fans often contain a ducted housing to direct outgoing air in a specific direction or across a heat sink; such a fan is also called a blower, blower fan, or squirrel-cage fan (because it looks like a hamster wheel).
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