Direct numerical simulation of turbulence in a salt-stratified fluid

Decaying turbulence in salt-stratified fluid with Schmidt number 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 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 , where is the kinematic viscosity and the Brunt-Vaisala frequency, decreases significantly due to the persistent conversion of potential energy into kinetic energy by the counter-gradient density flux.