In aviation, exhaust mixer is a feature of many turbofan engines, where the bypass (cold/slow) air is mixed with the core (hot/fast) exhaust gases, before exhausting to atmospheric pressure through a common (mixed flow) propelling nozzle.
The mixer reduces the velocity 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.
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 = 1/2mv2. 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.
The Trent 700 which powers the Airbus A330, has a common nozzle assembly which mixes the cold and hot flows.[1]
Apache AH-64 helicopter, with exhaust mixer to reduce IR signal
Annular - bypass and core streams are brought together co-annularly, mixing being achieved by the shearing 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 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 exhaust pipes (i.e. hot and cold) are avoided. Afterburning, 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.
exhaust, mixer, this, article, needs, additional, citations, verification, please, help, improve, this, article, adding, citations, reliable, sources, unsourced, material, challenged, removed, find, sources, news, newspapers, books, scholar, jstor, june, 2017,. This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Exhaust mixer news newspapers books scholar JSTOR June 2017 Learn how and when to remove this template message In aviation exhaust mixer is a feature of many turbofan engines where the bypass cold slow air is mixed with the core hot fast exhaust gases before exhausting to atmospheric pressure through a common mixed flow propelling nozzle Exhaust mixer of a JT8D engine of a Boeing 737 200 Contents 1 Benefits 2 Mixer types 3 See also 4 ReferencesBenefits Edit Hush kit mixer on the turbojet General Electric CJ805 of a Convair 880The mixer reduces the velocity 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 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 2mv2 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 The Trent 700 which powers the Airbus A330 has a common nozzle assembly which mixes the cold and hot flows 1 The PW4000 has separate exhaust nozzlesMixer types Edit Apache AH 64 helicopter with exhaust mixer to reduce IR signalAnnular bypass and core streams are brought together co annularly mixing being achieved by the shearing effect at the stream interface Forced hot and cold chutes intertwined force the two streams to mixMixing 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 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 exhaust pipes i e hot and cold are avoided Afterburning 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 See also EditChevron aeronautics References Edit Lufthans Technical Training Training Manual Airbus A330 ATA71 80 Engine RR Trent 700 page 30 http www fluent com solutions examples x178 htm Retrieved from https en wikipedia org w index php title Exhaust mixer amp oldid 1122729401, wikipedia, wiki, book, books, library,
