Shock-wave imaging by density recovery from intensity measurements

Mehdhi, Biswajit and Hegde, Gopalakrishna M and Reddy, Kalidevapura Jagannath and Roy, Debasish and Vasu, Ram Mohan (2018) Shock-wave imaging by density recovery from intensity measurements. In: APPLIED OPTICS, 57 (15). pp. 4297-4308.

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Abstract

A method for quantitative estimation of density variation in high-speed flow, which uses light as an interrogating tool, is described. The wavefront distortion of the interrogating beam induced by the compressible flow field is estimated quantitatively, in which the density gradient of the flow field is seen as refractive-index gradient by the probing beam. The distorted wavefront is measured quantitatively by using the cross-sectional intensities of the distorted wavefront along the optical axis. Iterative algorithms are developed using both deterministic (Gauss Newton) and stochastic (ensemble Kalman filter) update strategies to recover unknown parameters such as the phase of the wavefront or the refractive index distribution in the flow directly from the measured intensities. With phase recovered in the first step, a ray tomography algorithm is used to obtain the refractive index and density distributions in the flow from the phase. Experiments are conducted to quantitatively visualize the shock-wave induced flow field in a shock-tunnel facility. The reconstructed density cross sections, obtained using different reconstruction methods, are presented and compared with those obtained by solving the Navier Stokes equation using computational fluid dynamic routines. It is observed that the iterative algorithms always outperform those depending on solution of the transport-of-intensity equation. In particular, when using the iterative algorithms, the stochastic search scheme outperforms the Gauss Newton method. (C) 2018 Optical Society of America

Item Type:	Journal Article
Publication:	APPLIED OPTICS
Additional Information:	Copy right for this article belong toOPTICAL SOC AMER, 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA
Department/Centre:	Division of Mechanical Sciences > Aerospace Engineering(Formerly Aeronautical Engineering) Division of Mechanical Sciences > Civil Engineering Division of Interdisciplinary Sciences > Centre for Nano Science and Engineering Division of Physical & Mathematical Sciences > Instrumentation Appiled Physics
Date Deposited:	05 Jun 2018 15:47
Last Modified:	05 Jun 2018 15:47
URI:	http://eprints.iisc.ac.in/id/eprint/59951

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