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Schlieren

Switzerland, Schlieren
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Color schlieren image o the thermal plume rom a burning candle, disturbed by a breeze rom the right. Photographed by Gary S. Settles, Penn State University

"Schlieren" (rom German; singular "Schliere") are optical inhomogeneities in transparent material not visible to the human eye. Schlieren physics developed out o the need to produce high-quality lenses void o these inhomogeneities. These inhomogeneities are localized dierences in optical path length that cause light deviation. This light deviation is converted to shadow in a schlieren system.

History
Schlieren were irst observed by Robert HookeHooke, R., "O a New Property in the Air," "Micrographia", Observation LVIII,27-29, (665). in 665 using a large convex lens and two candles. One candle served as a light source. The warm air rising rom the second candle provided the schliere.
The conventional schlieren system is credited mostly to German physicist August Toepler. Toepler"s original system Toepler, A., "Beobachtungen nach einer neuen optischen Methode", Maximillan Cohen und Sohn, Bonn (864). was designed to detect schlieren in glass used to make lenses. In the conventional schlieren system Rienitz, J., "Schlieren Experiments 300 years ago," Nature "254", 293-295 (March 27, 975)., a point source is used to illuminate the test section containing the schliere. An image o this light is ormed 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:
\rac=\rac+\rac
where is the ocal length o the lens, is the distance rom the object to the lens and is the distance rom the image o the object to the lens. A knie edge at the point source-image location is positioned as to partially block some light rom reaching the viewing screen. The illumination o the image is reduced uniormly. A second lens is used to image the test section to the viewing screen. The viewing screen is located a conjugate distance rom the plane o the schliere.

Schlieren Flow Visualization

Schlieren low visualization is based on the delection o light by a reractive index gradientSettles, G. S., "Schlieren and shadowgraph techniques: Visualizing phenomena in transparent media," Berlin:Springer-Verlag, 200. The index gradient is directly related to low density gradient. The delected light is compared to undelected light at a viewing screen. The undisturbed light is partially blocked by a knie edge. The light that is delected toward or away rom the knie edge produces a shadow pattern depending upon whether it was previously blocked or unblocked. This shadow pattern is a light-intensity representation o the expansions (low density regions) and compressions (high density regions) which characterize low.

See also
* Mach-Zehnder intererometer
* Schlieren photography
* Shadowgraph
* Background Oriented Schlieren technique
* Schlieren imaging

Reerences


External links
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Category:Optics
Category:German words and phrases

de:Schliere
es:Eecto Schlieren
it:Metodo Schlieren
ja:シュリーレン現象
Dieser Artikel stammt aus der freien Enzyklopädie Wikipedia und kann dort bearbeitet werden. Der Text ist unter der Lizenz Creative Commons Attribution/Share Alike verfügbar. Fassung vom 17.09.2019 13:21 von den Wikipedia-Autoren.
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