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Direct numerical simulation of turbulence in a salt-stratified fluid

Published online by Cambridge University Press:  23 March 2020

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

Decaying turbulence in salt-stratified fluid with Schmidt number $700$ is investigated by direct numerical simulation. In the final period of decay, and after the Ozmidov scale becomes smaller than the Kolmogorov scale, potential-energy distribution due to salinity fluctuations shows large-scale clouds composed of structures smaller than the Kolmogorov scale. When these clouds appear, potential energy has a flat spectrum in the viscous-convective subrange, rather than a $k^{-1}$ spectrum observed initially before the stratification effect becomes significant. This transition occurs since the potential energy near the Kolmogorov scale or the primitive scale of stratified turbulence defined by $\sqrt{\unicode[STIX]{x1D708}^{\ast }/N^{\ast }}$, where $\unicode[STIX]{x1D708}^{\ast }$ is the kinematic viscosity and $N^{\ast }$ the Brunt–Väisälä frequency, decreases significantly due to the persistent conversion of potential energy into kinetic energy by the counter-gradient density flux.

JFM classification

Turbulent Flows: Stratified turbulence Turbulent Flows: Turbulence simulation Geophysical and Geological Flows: Internal waves
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 891 , 25 May 2020 , A19
Copyright
© The Author(s), 2020. Published by Cambridge University Press

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