From Event: SPIE Optical Engineering + Applications, 2017
Schlieren imaging has been an essential method for studying aerodynamic effects, particularly thermal convection, shock waves, and turbulent flows. This paper describes a compact portable digital focusing schlieren system that can be used to visualize relatively large fields for applications in ventilation design and aerodynamics research. Visualizing large fields is difficult using classical schlieren systems that employ collimated light because their field of view is limited by the size of the mirrors or lenses. Background-oriented schlieren systems are well-suited for visualizing large fields, but their sensitivity is limited by the need to simultaneously maintain focus on the background pattern and the test area. Lens and grid-based focusing schlieren systems are essentially hybrids between classical and background-oriented systems. They can visualize fields that are much larger than possible with classical schlieren systems, while providing more sensitivity than background-oriented schlieren systems. Using commercially available camera lenses and optics, fields up to several square meters can be visualized. A key innovation in the system presented here is that digital display devices are used to display the background pattern, which simplifies the optical system and reduces its size. To calibrate the system, proprietary software is used to analyze images acquired by the system’s digital camera, and then a background pattern is computed that is complementary to the cutoff grid. The calibration software also provides real-time background subtraction and contrast enhancement. The schlieren system is portable enough that it can be set up quickly in industrial facilities.
Drew L'Esperance and Benjamin D. Buckner, "Focusing schlieren systems using digitally projected grids," Proc. SPIE 10373, Applied Optical Metrology II, 103730R (Presented at SPIE Optical Engineering + Applications: August 09, 2017; Published: 23 August 2017); https://doi.org/10.1117/12.2274079.
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