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3-D visualization of thermal turbulence
(click on an image for a larger view)
The traditional shadowgraph technique is very useful for visualizing flow structure in a thermal system. The temperature variations cause density variations, which appear as changes in refractive index. When a parallel beam of light is sent through the system, the convective fluid casts a "shadow" . The 3D information is projected onto a 2D plane, and the structure along the path of the light beam is lost. To recover the full 3D information, we are developing a simple technique that uses two light sources and thus two sets of shadowgraphs. Correlations between the shadowgraphs produced by two separated light sources can be used to obtain three-dimensional information.
This experiment concerns Rayleigh-Bènard convection. A glycerol-water mixture, contained within a cubical box, is heated from below and cooled from above using a water circulator.
A close-up image of the convection cell.
Two light sources are used to visualize the convection cell.
The beams are projected through the lens and into the cell.
A red shadowgraph is produced by one light beam. The three-dimensional structure is projected onto a 2D plane (shown in B&W). Another shadowgraph is produced in green light. When the two images are analyzed by a computer program (which separates the two shadowgraphs obtained in different colors and calculates the cross-correlation between the two images), the 3D structure can be recovered.
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