Instrumentation, Techniques, and Measurement

Quantitative estimation of density variation in high-speed flows through inversion of the measured wavefront distortion

[+] Author Affiliations
Biswajit Medhi

Indian Institute of Science, Department of Instrumentation and Applied Physics, Bangalore 560012, India

Gopalkrishna Mahadeva Hegde

Indian Institute of Science, Centre for Nano Science and Engineering, Bangalore 560012, India

Kalidevapura Polareddy Jagannath Reddy

Indian Institute of Science, Department of Aerospace Engineering, Bangalore 560012, India

Debasish Roy

Indian Institute of Science, Department of Civil Engineering, Computational Mechanics Lab, Bangalore 560012, India

Ram Mohan Vasu

Indian Institute of Science, Department of Instrumentation and Applied Physics, Bangalore 560012, India

Opt. Eng. 53(12), 124107 (Dec 23, 2014). doi:10.1117/1.OE.53.12.124107
History: Received September 8, 2014; Accepted November 21, 2014
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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.

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© 2014 Society of Photo-Optical Instrumentation Engineers

Citation

Biswajit Medhi ; Gopalkrishna Mahadeva Hegde ; Kalidevapura Polareddy Jagannath Reddy ; Debasish Roy and Ram Mohan Vasu
"Quantitative estimation of density variation in high-speed flows through inversion of the measured wavefront distortion", Opt. Eng. 53(12), 124107 (Dec 23, 2014). ; http://dx.doi.org/10.1117/1.OE.53.12.124107


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