Is isotropy restored at small scales in freely decaying strongly stratified turbulence ?

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We analyse the scale-dependent anisotropy of homogeneous stratified turbulence. The Ozmidov scale l_N (Ozmidov 1965) helps to compare the relative effects of inertia and of the buoyancy force, and thus to quantify the rise of anisotropy in different scale ranges: at large scales l >> l_N the anisotropy due to strong stratification is dominant, whereas at small scales l << l_N, universal 3D isotropic characteristic of turbulence appear to be restored. We investigate the corresponding dynamics using Direct Numerical Simulations (DNS) in freely decaying turbulence at different stratification rates. We confirm the return to isotropy of the small scales by analyzing the orientation-dependent power spectrum and poloidal/toroidal/density energy modes. To some extent, many characteristics of isotropic universality are restored at small scales but, surprisingly, the density spectrum (also potential energy spectrum) plays a particular role.