3D Visualization of Thermal Turbulence


  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-Bénard 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 here projected onto a 2-D 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.