In aviation, an exhaust mixer / flow mixer is a feature of many turbofan engines, where slower, colder bypass air is mixed with faster, hotter core

exhaust gas Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline (petrol), diesel fuel, fuel oil, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through ...

es, before exhausting to atmospheric pressure through a common (mixed flow) propelling

nozzle A nozzle is a device designed to control the direction or characteristics of a fluid flow (specially to increase velocity) as it exits (or enters) an enclosed chamber or pipe (material), pipe. A nozzle is often a pipe or tube of varying cross ...

Benefits

Convair 880 Lisa Marie Graceland Memphis TN 2013-04-01 028

The mixer reduces the

velocity Velocity is a measurement of speed in a certain direction of motion. It is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of physical objects. Velocity is a vector (geometry), vector Physical q ...

of the core exiting air, and consequently, reducing the amount of noise produced. Additionally, the temperature of the exhaust is reduced, contributing to the overall reduction of the thermal signature of the aircraft. This attribute is critical in military aircraft where thermal detection or heat-seeking weapons are used, in particular stealth

aircraft An aircraft ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...

. Ideally, a mixer is also a performance benefit to increasing thrust. The exhaust thrust from a jet engine is equal to exhaust mass flow times exhaust velocity, i.e., ''Thrust = ṁv'', while the energy to make that thrust is given by ''Energy'' = 1/2''mv''². A mixer helps reduce the fastest exhaust velocities from the core of the engine, while making the average exhaust velocity faster, producing more thrust with the same energy. File:Trent 700 - DSC 8123-F-WWCR - MSN 1462 (10513329855) (cropped).jpg, The Trent 700 which powers the

Airbus A330 The Airbus A330 is a wide-body airliner developed and produced by Airbus. Airbus began developing larger A300 derivatives in the mid–1970s, giving rise to the A330 twinjet as well as the Airbus A340 quadjet, and launched both designs along ...

, has a common nozzle assembly which mixes the cold and hot flows.Lufthans Technical Training, Training Manual Airbus A330, ATA71-80 Engine RR Trent 700, page 30 File:Airbus A330-200F(F-WWYE) (4337113707).jpg, The PW4000 has separate exhaust nozzles File:Northrop Tacit Blue rear R&D NMUSAF 25Sep09 (14600452315).jpg, Slit shaped tail exhaust

Northrop Tacit Blue The Northrop Tacit Blue is a technology demonstrator aircraft created to demonstrate that a low-observable Stealth technology, stealth surveillance aircraft with a low probability of intercept radar, low-probability-of-intercept radar (LPIR) and ...

Mixer types

*Annular - bypass and core streams are brought together co-annularly, mixing being achieved by the

shearing Sheep shearing is the process by which the woollen fleece of a sheep is cut off. The person who removes the sheep's wool is called a '' shearer''. Typically each adult sheep is shorn once each year (depending upon dialect, a sheep may be sai ...

effect at the stream interface *Forced - hot and cold chutes, intertwined, force the two streams to mix Mixing efficiency is defined in a number of ways, but simply, compares the actual thrust gain (due to mixing) to that of the ideal case. Annular mixers have a low

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...

loss, but a low mixing efficiency. Forced mixers can have a high mixing efficiency, but this is offset by a high pressure loss. Mixers are extremely common on military turbofans, since long

coaxial In geometry, coaxial means that several three-dimensional linear or planar forms share a common axis. The two-dimensional analog is ''concentric''. Common examples: A coaxial cable has a wire conductor in the centre (D), a circumferential ou ...

exhaust pipes (i.e. hot and cold) are avoided.

Afterburning An afterburner (or reheat in British English) is an additional combustion component used on some jet engines, mostly those on military aircraft, military supersonic aircraft. Its purpose is to increase thrust, usually for supersonic flight, ta ...

, with the associated variable area nozzle, is also easier to accommodate. Some high bypass ratio (e.g. civil) turbofans now feature a mixer, the advantage being a small thrust gain, which improves specific fuel consumption. Although the mixing process is not thorough, there is a jet noise benefit as well.

References

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External links

Gas turbines Missile countermeasures Stealth technology

Benefits

Mixer types

See also

References

External links