Physics – Optics
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........24p&link_type=abstract
Thesis (PH.D.)--STANFORD UNIVERSITY, 1994.Source: Dissertation Abstracts International, Volume: 55-07, Section: B, page: 2976.
Physics
Optics
1
Image Processing
Scientific paper
A diagnostic for turbulent flows is described which provides instantaneous 3-D flowfield distributions by rapidly acquiring a series of 2-D flowfield distributions from successive planes within the flow. Visualization of successive flow planes is achieved by sweeping a laser sheet across the flow using a 30,000-RPM polygon scanner mirror. As successive flow planes are illuminated by the laser sheet, a high-speed image converter camera digitally records 2-D planar images of Mie- or fluorescence-scattered light at the rate of 10 million frames per second. For each 3-D measurement, up to sixteen 2-D images are collected with a total recording time of under 1.6 microseconds. After a set of planar images is recorded, the images are stacked by postprocessing software to form an instantaneous 3-D data array. The resulting information is suitable for a wide variety of analysis with respect to fundamental properties of the flow. The high-speed camera for this work was constructed from a commercial image converter camera, custom fiber optics, and an astronomy-grade CCD camera. A 400 x 700 portion of the CCD array was optically coupled to the output of the image converter by a tapered fiber-optic bundle. This custom recording system provides 2.5 times greater sensitivity than commercially available lens-coupled CCDs. Other performance parameters of this unique imaging system have been characterized, including the system gain, noise, and resolution. Several image distortion problems have also been characterized, and correction models formulated and implemented in the postprocessing software. The measurement technique, imaging hardware, and postprocessing software represent a complete and practical diagnostic as demonstrated through numerous applications of the system. First, the system was used to measure 3 -D soot distributions in several hydrocarbon diffusion flames. The measurements are displayed through various methods of volume rendering which reveal numerous interesting aspects of these flows. The imaging system has also been applied for 3-D planar laser-induced measurements in an acetone -seeded air jet. Finally, the system has been applied to the HTGL supersonic mixing layer facility, providing results that vividly demonstrate the potential of instantaneous 3-D planar imaging as a useful diagnostic for a wide variety of turbulent flows.
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