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Optical Engineering

Quantitative estimation of density variation in high-speed flows through inversion of the measured wavefront distortion
Author(s): Biswajit Medhi; Gopalkrishna M. Hegde; Kalidevapura Polareddy Jagannath Reddy; Debasish Roy; Ram Mohan Vasu
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Paper Abstract

A simple method employing an optical probe is presented to measure density variations in a hypersonic flow obstructed by a test model in a typical shock tunnel. The probe has a plane light wave trans-illuminating the flow and casting a shadow of a random dot pattern. Local slopes of the distorted wavefront are obtained from shifts of the dots in the pattern. Local shifts in the dots are accurately measured by cross-correlating local shifted shadows with the corresponding unshifted originals. The measured slopes are suitably unwrapped by using a discrete cosine transform based phase unwrapping procedure and also through iterative procedures. The unwrapped phase information is used in an iterative scheme for a full quantitative recovery of density distribution in the shock around the model through refraction tomographic inversion. Hypersonic flow field parameters around a missile shaped body at a free-stream Mach number of 5.8 measured using this technique are compared with the numerically estimated values.

Paper Details

Date Published: 23 December 2014
PDF: 7 pages
Opt. Eng. 53(12) 124107 doi: 10.1117/1.OE.53.12.124107
Published in: Optical Engineering Volume 53, Issue 12
Show Author Affiliations
Biswajit Medhi, Indian Institute of Science (India)
Gopalkrishna M. Hegde, Indian Institute of Science (India)
Kalidevapura Polareddy Jagannath Reddy, Indian Institute of Science (India)
Debasish Roy, Indian Institute of Science (India)
Ram Mohan Vasu, Indian Institute of Science (India)

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