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Flow visualization using reflective flakes

Published online by Cambridge University Press:  18 August 2011

Susumu Goto ,
Shigeo Kida  and
Shohei Fujiwara
Susumu Goto*
Affiliation:
Department of Mechanical Engineering, Okayama University, 3-1-1, Tsushima-naka, Kita, Okayama 700-8530, Japan
Shigeo Kida
Affiliation:
Department of Mechanical Engineering, Doshisha University, 1-3, Tatara-miyakodani, Kyotanabe 610-0394, Japan
Shohei Fujiwara
Affiliation:
Department of Mechanical Engineering and Science, Kyoto University, Yoshida-Honmachi, Sakyo, Kyoto 606-8501, Japan
*
†Email address for correspondence: [email protected]
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Abstract

The pattern in an image of flow visualizations using reflective flakes stems from their non-uniform orientation rather than their spatial accumulation. It is shown, based on the assumption that flakes are infinitely thin elliptic discs without inertia, that the temporal evolution of their orientations is identical to that for infinitesimal material surface elements. In general, bright regions in a visualized image are the superposition of those where the flake (i.e. the material surface element) orientation is isotropic and those where flakes tend to align in the direction for which the incident rays are reflected into the line of sight. A non-trivial example of the visualization of a steady flow in a precessing sphere is given to verify these conclusions.

JFM classification

Mathematical Foundations: General fluid mechanics Mixing: Turbulent mixing
Type
Papers
Information
Journal of Fluid Mechanics , Volume 683 , 25 September 2011 , pp. 417 - 429
Copyright
Copyright © Cambridge University Press 2011

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Goto et al. supplementary movie

Movie 1. Experimental apparatus. The precession (at the Reynolds number 80000; the precession rate 0.002) of a spherical cavity (radius 90 mm; filled with degassed water with reflective flakes) is driven by two stepper motors. The acyclic vessel is cylindrical, and an observation window is placed at the bottom of the cylinder.

Download Goto et al. supplementary movie(Video)
Video 10 MB

Goto et al. supplementary movie

Movie 2. Temporal evolution of the flake visualisation of the steady flow in a precessing sphere for the duration of 200 spin periods. The initial condition is the solid-body rotational flow at the Reynolds number 80000, and a weak precession (the rate of which is 0.002) is added, impulsively. A beautiful pattern, which seems quite robust, appears after about 50 spin periods. Frame rate is the twice of the real time.

Download Goto et al. supplementary movie(Video)
Video 11.3 MB