29 September 1995 Tomographic holographic interferometry for unsteady compressible flows
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The study of an underexpanded compressible jet using pulsed, phase- shifted interferometry in conjunction with a 9 beam tomographic illumination system is described. A plane wave holographic interferometer using a pulsed ruby laser has been adapted to provide multiple illumination directions of a volume that is approximately 4 centimeters on a side. This set-up is being used to study the transient behavior of compressible jets and may be operated using double-exposure holographic interferometry to study the instantaneous behavior of the flow; alternatively, the system may be operated in a double-pulse mode to study the fluctuations in the flow. The tomographic reconstructions are made using a Fourier-Bassel expansion. To illustrate the performance of the system, an underexpanded nozzle flow producing a series of compression-rarefaction 'diamonds' was studied. The images show sharp reconstructions of the compression-rarefaction diamond pattern as well as some interesting secondary flow structures.
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Brenda H. Timmerman, David W. Watt, "Tomographic holographic interferometry for unsteady compressible flows", Proc. SPIE 2546, Optical Techniques in Fluid, Thermal, and Combustion Flow, (29 September 1995); doi: 10.1117/12.221533; https://doi.org/10.1117/12.221533

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