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Jets generated by a sphere moving vertically in a stratified fluid

Published online by Cambridge University Press:  24 September 2009

H. HANAZAKI ,
K. KASHIMOTO  and
T. OKAMURA
H. HANAZAKI*
Affiliation:
Department of Mechanical Engineering and Science, Kyoto University, Yoshida-Honmachi, Sakyo-Ku, Kyoto 606-8501, Japan
K. KASHIMOTO
Affiliation:
Department of Mechanical Engineering and Science, Kyoto University, Yoshida-Honmachi, Sakyo-Ku, Kyoto 606-8501, Japan
T. OKAMURA
Affiliation:
Department of Mechanical Engineering and Science, Kyoto University, Yoshida-Honmachi, Sakyo-Ku, Kyoto 606-8501, Japan
*
†Email address for correspondence: hanazaki@mech.kyoto-u.ac.jp
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Abstract

Experiments are performed on the flow past a sphere moving vertically at constant speeds in a salt-stratified fluid. Shadowgraph method and fluorescent dye are used for the flow visualization, and particle image velocimetry is used for the velocity measurement in the vertical plane. Vertical ‘jets’ or columnar structures are observed in the shadowgraph for all the Froude numbers Fr(0.2 ≲ Fr ≲ 70) investigated, and the wake structures in the whole parameter space of Fr and the Reynolds number Re(30 ≲ Re ≲ 4000) are classified into seven types, five of which are newly found. Those include two types of thin jets, one of which is short with its top disturbed by internal waves to have a peculiar ‘bell-shaped’ structure, while the other has an indefinitely long length. There are two other new types of jet with periodically generated ‘knots’, one of which is straight, while the other has a spiral structure. A simply meandering jet has also been found. These wake structures are significantly different from those in homogeneous fluids except under very weak stratification, showing that the stratification effects on vertical motion are much more significant than those on horizontal motion.

Type
Papers
Information
Journal of Fluid Mechanics , Volume 638 , 10 November 2009 , pp. 173 - 197
Copyright
Copyright © Cambridge University Press 2009

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