Shadowgraph

Source: Wikipedia, the free encyclopedia.
For other uses, see Shadowgraphy (disambiguation).

Shadowgraph is an optical method that reveals non-uniformities in

flow visualisation
.

In principle, a difference in temperature, a different gas, or a

shadows. The plume of hot air rising from a fire, for example, can be seen by way of its shadow cast upon a nearby surface by the uniform sunlight
.

Sunlight shadowgraph

Some aquatic predators detect their transparent prey by way of their shadows cast upon the ocean floor. It was Robert Hooke[1] who first scientifically demonstrated the sunlight shadowgraph and Jean-Paul Marat[2] who first used it to study fire. A modern account of shadowgraphy is given by Gary S. Settles.[3]

Applications

Applications of shadowgraphy in science and technology are very broad. It is used in

explosions, and in the testing of glass
. Ideal for identification of flow patterns.

Shadowgram (Shadowgraph)

According to

Laplacian) of the refractive index
field in the transparent medium under study. Once the distance from the transparent disturbance to the cast shadow becomes too large, then the shadow no longer constitutes a useful representation of the disturbance that caused it.

Cartoons

The shadowgraph and shadowgram have been used in animation, where they reinforce the cartoon's realism. One first use was made by

Silly Symphonies.[5]

Postcards

Additionally the term Shadowgraph was used by English postcard publishers E.T.W. Dennis & Sons Ltd. of London and Scarborough for a series of 'Hold up to the Light' postcards in the 1950s. In these a saucy image can be seen through what seems an innocent picture when a light is shone through the card.[6]

Gallery

  • a) prehistoric shadowgraphy, b) sunlight shadowgram of a martini glass, c) "focused" shadowgram of a common firecracker explosion, d) "Edgerton" shadowgram of the firing of an AK-47 assault rifle
    a) prehistoric shadowgraphy, b) sunlight shadowgram of a martini glass, c) "focused" shadowgram of a common firecracker explosion, d)
    AK-47 assault rifle
  • Shadowgram of the turbulent plume of hot air rising from a home-barbecue gas grill.
    Shadowgram of the turbulent plume of hot air rising from a home-barbecue gas grill.
  • "Edgerton" shadowgraph of bullet in flight
    "Edgerton"
    shadowgraph of bullet in flight
  • Shadowgram of shock waves from a supersonic bullet fired from a rifle. The shadowgraph optical technique reveals that the bullet is moving at a Mach number of about 1.9. Left- and right-running bow waves and tail waves stream back from the bullet, and its turbulent wake is also visible. To the right of the frame are seen unburned powder particles from the cartridge, themselves traveling slightly subsonic so that each of them produces a curved bow shock wave.
    Shadowgram of shock waves from a supersonic bullet fired from a rifle. The shadowgraph optical technique reveals that the bullet is moving at a Mach number of about 1.9. Left- and right-running bow waves and tail waves stream back from the bullet, and its turbulent wake is also visible. To the right of the frame are seen unburned powder particles from the cartridge, themselves traveling slightly subsonic so that each of them produces a curved bow shock wave.

See also

References

  1. ^ Hooke, R., "Of a New Property in the Air," Micrographia, Observation LVIII,217-219, London(1665).
  2. ^ Marat, J.-P., Recherches physiques sur le feu, Paris, France:Cl. Ant. Jombert, 1780.
  3. ^ Settles, G. S., Schlieren and shadowgraph techniques: Visualizing phenomena in transparent media, Berlin:Springer-Verlag, 2001.
  4. ^ Weinberg, F.J., Optics of flames: including methods for the study of refractive index fields in combustion and aerodynamics, London:Butterworths, 1963.
  5. ISBN 88-86155-27-1
    p 46
  6. ^ "MetroPostcard Publishers D". Metropolitan Postcard Club of New York City. Archived from the original on 2008-09-15. Retrieved 2008-10-02.


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