Direct numerical simulation of decaying stratified turbulence with extreme scale separation

Stably stratified turbulence (SST) is a model flow for understanding fluid flows that are highly intermittent and anisotropic at large scales. The understanding derived from SST is important for applications ranging from climate modeling, to pollution mitigation, to deep sea mining, to military operations over cold land or ice. SST is also valuable for enhancing fundamental turbulence theory on turbulent/non-turbulent interfaces, internal intermittency, and anisotropic multi-scale energetics. In all turbulent flows, dynamic range, or the ratio of the largest the smallest length scales, has a profound effect on the fluid dynamics. Dynamic range is characterized by the Reynolds number, Re. SST, though, is at least a two parameter problem with Re characterizing the overall dynamic range and Froude number Fr describing the range of comparatively large length scales strongly affected by buoyancy. In direct numerical simulations (DNSs), at least four decades of scale separation is required to resolve the horizontal scales in the strongly stratified regime. Here we present results from simulations using up to 24000×24000×6000 grid point and generating about 55 TB per snapshot of the flow field in time. We show the dynamics when there is sufficient dynamic range for how the flow to be fully turbulent.