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| | The name of the author is Jayson. It's not a common factor but what I like doing is to climb but I don't have the time recently. I've always cherished living in Kentucky but now I'm contemplating other options. My day job is a travel agent.<br><br>My web-site; phone psychic ([http://appin.co.kr/board_Zqtv22/688025 appin.co.kr]) |
| {{distinguish2|the mineral [[diamond]]}}
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| [[File:J58 AfterburnerT.jpeg|thumb|300px|A statically mounted [[Pratt & Whitney J58 engine]] on full [[afterburner]] while disposing of the last of the [[SR-71]] fuel prior to program termination. The bright areas seen in the exhaust are known as shock diamonds.]]
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| '''Shock diamonds''' (also known as '''Mach diamonds''', '''Mach disks''', '''Mach rings''', '''doughnut tails''' or '''thrust diamonds''') are a formation of [[standing wave]] patterns that appears in the [[supersonic]] [[exhaust plume]] of an aerospace propulsion system, such as a supersonic [[jet engine]], [[rocket]], [[ramjet]], or [[scramjet]], when it is operated in an atmosphere. The diamonds are formed from a complex flow field and are visible due to the ignition of excess fuel. Mach diamonds (or disks) are named for [[Ernst Mach]], the physicist who first described them.<ref>Norman, p. 48</ref>
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| ==Mechanism==
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| [[File:SR-71 Blackbird afterburn.jpg|thumb|left|200px|Shock diamonds behind a [[Lockheed SR-71 Blackbird]] in flight]]
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| Shock diamonds form when the supersonic exhaust from a nozzle is slightly over or under-expanded, meaning that the [[pressure]] of the gases exiting the nozzle is different from the ambient [[air pressure]].<ref name=aero>{{cite web|last=Scott|first=Jeff|title=Shock Diamonds and Mach Disks|url=http://www.aerospaceweb.org/question/propulsion/q0224.shtml|publisher=Aerospaceweb.org|accessdate=6 November 2011|date=17 April 2005}}</ref> The exhaust is generally over-expanded at low altitudes where air pressure is higher, and under-expanded at higher altitudes.
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| [[File:South Carolina F-16 taking off in Afghanistan.jpg|thumb|300px|Mach diamonds from an [[General Dynamics F-16 Fighting Falcon|F-16]] taking off with afterburner]]
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| As the flow exits the nozzle, ambient air pressure will either expand or compress the flow; over-expanded flow is compressed while under-expanded flow expands.<ref name=aero/> The compression or expansion is caused by [[oblique shock wave]]s inclined at an angle to the flow. When the compressed flow becomes parallel to the center line, a shock wave perpendicular to the flow forms, called a [[normal shock wave]]. The first shock diamond is located here and the space between it and the nozzle is called the "zone of silence".<ref name=lcms/> The distance from the nozzle to the first shock diamond can be approximated by:
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| :<math>x = 0.67 D_0\sqrt{\frac{P_0}{P_1}}</math>
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| [[File:Kluft-photo-MSS-Xoie-LLC-L2-landing-Img 1282.jpg|thumb|200px|Shock diamonds beneath [[Masten Space Systems]] Xoie rocket during [[Lunar Lander Challenge]] winning landing]]
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| where x is the distance, D<sub>0</sub> is the nozzle diameter, P<sub>0</sub> is flow pressure and P<sub>1</sub> is atmospheric pressure.<ref name=lcms>{{cite book|last=Niessen|first=Wilfried M. A.|title=Liquid chromatography-mass spectrometry, Volume 79|year=1999|publisher=CRC Press|isbn=978-0-8247-1936-4|url=http://books.google.com/books?id=oSnKlgDBzJEC|page=84}}</ref>
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| As the exhaust passes through the normal shock wave, its temperature increases, igniting excess fuel and causing the glow that makes the shock diamonds visible.<ref name=aero/> The illuminated regions either appear as disks or [[diamond (shape)|diamond]]s, giving them their name.
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| At each shock diamond, the flow becomes compressed enough that it expands outward in a set of expansion waves called the [[expansion fan]]. Eventually the flow expands enough so that its pressure is again below ambient, at which point the expansion fan reflects off the [[contact discontinuity]] (the outer edge of the flow). The reflected waves, called the [[compression fan]], cause the flow to compress.<ref name=aero/> If the compression fan is strong enough, another oblique shock wave will form, creating a second shock diamond. The pattern of disks would repeat indefinitely if the gases were ideal and frictionless,<ref name=aero/> however, [[turbulent]] shear at the contact discontinuity causes the wave pattern to dissipate with distance.<ref name=fiu>{{cite web|title=Exhaust Gases' Diamond Pattern|url=http://www.allstar.fiu.edu/aero/rocket3.htm|publisher=Florida International University|accessdate=6 November 2011|date=12 March 2004}}</ref>
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| ==Alternative sources==
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| Shock diamonds are most commonly associated with jet and rocket propulsion, but they can form in other systems.
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| ===Artillery===
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| When artillery pieces are fired, gas exits the cannon muzzle at supersonic speeds and produces a series of shock diamonds. The diamonds cause a bright "muzzle flash" which can expose the location of gun emplacements to the enemy. It was found that when the ratio between the flow pressure and atmospheric pressure is close to one, the shock diamonds were greatly minimized. Adding a flare to the end of the muzzle balances the pressures and prevents shock diamonds.<ref>Norman, p. 41</ref>
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| ===Volcanism===
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| Some [[volcano]]es have been shown to produce jets containing shock diamonds. This makes the base of the eruption supersonic, leading to the same dynamics that produce shock diamonds. These highly destructive jets have occurred in gas-rich volcanoes such as [[Mount St. Helens]] and [[Krakatoa]].<ref>Norman, p. 45</ref>
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| ===Radio jets===
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| Some [[radio jets]], powerful jets of plasma that emanate from [[quasar]]s and [[radio galaxies]], are observed to have regularly spaced knots of enhanced radio emissions.<ref>Norman, p. 68</ref> The jets travel at supersonic speed through a thin "atmosphere" of gas in space,<ref>Norman, p. 51</ref> so it is hypothesized that these knots are shock diamonds.
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| == See also ==
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| {{Commons category|Shock diamonds}}
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| * [[Afterburner]]
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| * [[Exhaust gas]]
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| * [[Plume (hydrodynamics)]]
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| * [[Rocket engine nozzle]]
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| * [[Shock wave]]
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| ==Notes==
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| {{Reflist}}
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| ==References==
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| *{{cite web|title=Supersonic Jets|last1=Norman|first1=Michael L.|last2=Winkler|first2=Karl-Heinz A.|url=http://library.lanl.gov/cgi-bin/getfile?12-03.pdf|work=LOS ALAMOS SCIENCE|publisher=Los Alamos National Lab|accessdate=6 November 2011|date=Spring/Summer 1985}}
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| == External links ==
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| * [http://science.nasa.gov/science-news/science-at-nasa/2007/04may_methaneblast/ "Methane blast"] - shock diamonds forming in NASA's methane engine built by [[XCOR Aerospace]], NASA website, 4 May 2007
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| [[Category:Physical phenomena]]
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| [[Category:Shock waves]]
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| [[Category:Aerospace]]
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The name of the author is Jayson. It's not a common factor but what I like doing is to climb but I don't have the time recently. I've always cherished living in Kentucky but now I'm contemplating other options. My day job is a travel agent.
My web-site; phone psychic (appin.co.kr)