schlieren

Schlieren were first observed by Robert HookeHooke, R. (1665), "Of a New Property in the Air", Micrographia, Observation LVIII, pp. 217–219, London. in 1665 using a large concave lens and two candles. One candle served as a light source. The warm air rising from the second candle provided the schliere.

The conventional schlieren system is credited mostly to German physicist August Toepler, though Jean Bernard Léon Foucault invented the method in 1859 that Toepler improved upon{{Citation needed|date=February 2025}}. Toepler's original systemToepler, A. (1864), Beobachtungen nach einer neuen optischen Methode, Maximillan Cohen und Sohn, Bonn. was designed to detect schlieren in glass used to make lenses. In the conventional schlieren system,{{cite journal|doi=10.1038/254293a0|title=Schlieren experiment 300 years ago|year=1975|last1=Rienitz|first1=J.|journal=Nature|volume=254|issue=5498|pages=293–295|bibcode=1975Natur.254..293R|s2cid=4288641}} a point source is used to illuminate the test section containing the schliere. An image of this light is formed using a converging lens (also called a schlieren lens). This image is located at the conjugate distance to the lens according to the thin lens equation:

$\backslash frac\{1\}\{f\}=\backslash frac\{1\}\{d\_o\}+\backslash frac\{1\}\{d\_i\}$

where $f$ is the focal length of the lens, $d\_o$ is the distance from the object to the lens and $d\_i$ is the distance from the image of the object to the lens. A knife edge at the point source-image location is positioned as to partially block some light from reaching the viewing screen. The illumination of the image is reduced uniformly. A second lens is used to image the test section to the viewing screen. The viewing screen is located a conjugate distance from the plane of the schliere.

File:Inlet shock waves at Mach 2.jpg Pratt & Whitney J58 engine inlet at Mach 2]]

Schlieren flow visualization is based on the deflection of light by a refractive index gradientSettles, G. S. (2001), Schlieren and shadowgraph techniques: Visualizing phenomena in transparent media, Berlin:Springer-Verlag.{{ISBN|978-3540661559}} The index gradient is directly related to flow density gradient. The deflected light is compared to undeflected light at a viewing screen. The undisturbed light is partially blocked by a knife edge. The light that is deflected toward or away from the knife edge produces a shadow pattern depending upon whether it was previously blocked or unblocked. This shadow pattern is a light-intensity representation of the expansions (low density regions) and compressions (high density regions) which characterize the flow.

The schlieren effect is often used in video projector technologies. The basic idea is some device, such as a liquid crystal light valve, is used to produce schlieren distortions in a controlled manner and these are projected on a screen to produce the desired image. Projection display systems such as the now-obsolete Eidophor and Talaria have used variations of this approach as far back as 1940.Brennesholtz, M.S. and Stupp, E.H. (2008), Projection Displays, John Wiley & Sons, p. 259 ff. {{ISBN|978-0-470-51803-8}}

• Background-oriented schlieren technique
• Laser schlieren deflectometry
• Mach–Zehnder interferometer
• Moire deflectometry
• Schlieren imaging
• Schlieren photography
• Shadowgraph
• Synthetic schlieren

{{Commons category|Schlieren imaging}}

{{wiktionary|schlieren}}

• Background oriented schlieren for flow visualisation in hypersonic impulse facilities
• [http://espace.library.uq.edu.au/eserv.php?pid=UQ:8810&dsID=SreekanthRughuna.pdf Visualisation of supersonic flows in shock tunnels using Background Oriented Schlieren (BOS) technique]
• [http://sciencehack.com/videos/view/_gKNhGbsEf4 Video on Schlieren photographs]
• [https://www.youtube.com/watch?v=fJIe0kTbdGc Schlieren on YouTube]

Category:Optics

Category:Articles containing video clips

ja:シュリーレン現象