Machsch knot

Mach knots in the exhaust of a Lockheed SR-71

Mach node (also known as Mach-diamonds , Mach-slices , Mach-rings , shock diamonds and thrust diamonds ) are a visible formation of standing wave patterns in gases, such as for example in the supersonic thrust jet of rocket and jet engines , as well as ramjet engines occur. They are named after the physicist Ernst Mach , who first described them.

The phenomenon also occurs in high-speed flame spraying .

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  Afterburner of a Pratt & Whitney J58 engine

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  expanding supersonic hot gas jet with compression bursts from an HVOF burner

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  Thrust jet of pixels of Armadillo Aerospace

The nodes are formed from a complex flow field and are visible through the abrupt changes in local density and pressure as a result of standing shock waves . The shock wave formation is not caused by a pulsating power of the turbine or the afterburner, but is a non- isentropic gas dynamic effect that occurs due to the compressibility and the high speed of the exhaust gas jet.

See also

• Rankine-Hugoniot condition
• Node surface

literature

• Michael L. Norman, Karl-Heinz A. Winkler: Supersonic Jets . In: Los Alamos Science . tape July 12 , 1985, p. 38-71 (English, online (7.7 MB) ).
• Detlef Schinköth: Laser scatter diagnostics in comparison with emission spectroscopy on a free-jet plasma. Dissertation, University of Stuttgart 2001, pp. 45–51, Figure 4.6 on p. 46 ( online , PDF; 814 kB)
• Heinz Voggenreiter : Process optimization of high-speed flame spraying for the production of load-bearing structures of the alloys 316L and Inconel 718. Dissertation. Technical University Freiberg 1996. Utz, Munich 1996, ISBN 3-89675-150-6 , p. 10 ( Google books ).