Analytical Technologies Singapore

Schlieren imaging is based on the deflection of light beams crossing gradients of the index of refraction in a transparent medium. These index of refraction gradients can be introduced by density discontinuities in a fluid or in mixing processes of different optical materials. Schlieren is a line-of-sight imaging technique allowing only a qualitative flow visualization.

The digital version of Schlieren imaging is called Background Oriented Schlieren (BOS) or Synthetic Schlieren based on Digital Image Correlation (DIC)

BOS is a line-of-sight imaging technique and measures locally the density gradient as an integrated value over the line-of-sight. In practice, only a random dot pattern in the background of the flow is imaged with a high resolution camera before and during the test. By comparing the two pictures (or more precisely correlating the two patterns similar to the image correlation in PIV) the local displacement of the background pattern can be used to provide lateral information on path-integrated refractive index variations.

LaVision’s Tomo-BOS imaging systems measure quantitatively density or temperature fields in 3D using multiple camera BOS projections. This 3D imaging technique requires an accurate geometrical calibration of the multi-camera system and an iterative tomographic reconstruction algorithm.


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