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Density distribution in the flow past a sphere descending in a salt-stratified fluid

Published online by Cambridge University Press:  29 September 2021

Shinya Okino Open the ORCID record for Shinya Okino [Opens in a new window] ,
Shinsaku Akiyama ,
Koki Takagi  and
Hideshi Hanazaki Open the ORCID record for Hideshi Hanazaki [Opens in a new window]
Shinya Okino
Affiliation:
Department of Mechanical Engineering and Science, Kyoto University, Kyoto daigaku-katsura 4, Nishikyo-ku, Kyoto615-8540, Japan
Shinsaku Akiyama
Affiliation:
Department of Mechanical Engineering and Science, Kyoto University, Kyoto daigaku-katsura 4, Nishikyo-ku, Kyoto615-8540, Japan
Koki Takagi
Affiliation:
Department of Mechanical Engineering and Science, Kyoto University, Kyoto daigaku-katsura 4, Nishikyo-ku, Kyoto615-8540, Japan
Hideshi Hanazaki*
Affiliation:
Department of Mechanical Engineering and Science, Kyoto University, Kyoto daigaku-katsura 4, Nishikyo-ku, Kyoto615-8540, Japan
*
†Email address for correspondence: [email protected]
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Abstract

The density distribution around a sphere descending in a salt-stratified fluid is measured by the laser-induced fluorescence (LIF) method. The corresponding velocity distribution is measured by particle image velocimetry (PIV), and numerical simulation is also performed to supplement the observations by LIF and PIV. In steady flow, LIF observes a thin and vertically long structure which corresponds to a buoyant jet. The bell-shaped structure, which appears under strong stratification and moderate Reynolds number (Froude number $Fr \lesssim 3$, Reynolds number $50 \lesssim Re \lesssim 500$), is also identified. The measured density distributions in the salinity boundary layer and in the jet agree with the numerical simulations which use the Schmidt number of the fluorescent dye ($Sc \sim 2000$). The initially unsteady process of the jet formation is also investigated. Under weak stratification, the LIF shows an initial development of an axisymmetric rear vortex as observed in homogeneous fluids. However, as time proceeds and the effect of stratification becomes significant, the vortex shrinks and disappears, while the jet extends vertically upward. Under strong stratification, a thin jet develops without generating a rear vortex, since the effect of stratification becomes significant in a short time before the vortex is generated.

JFM classification

Geophysical and Geological Flows: Stratified flows
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 927 , 25 November 2021 , A15
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Copyright
© The Author(s), 2021. Published by Cambridge University Press

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