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Direct numerical simulation of turbulence in a salt-stratified fluid
Published online by Cambridge University Press: 23 March 2020
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.
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- © The Author(s), 2020. Published by Cambridge University Press
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