Journal
PHYSICS OF FLUIDS
Volume 23, Issue 6, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.3599699
Keywords
flow instability; flow simulation; numerical analysis; stratified flow; turbulence; vortices
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Funding
- Natural Sciences and Engineering Research Council of Canada
- University of Waterloo
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Numerical simulations of forced stratified turbulence are presented, and the dependence on horizontal resolution and grid aspect ratio is investigated. Simulations are designed to model the small-scale end of the atmospheric mesoscale and oceanic submesoscale, for which high horizontal resolution is usually not feasible in large-scale geophysical fluid simulations. Coarse horizontal resolution, which necessitates the use of thin grid aspect ratio, yields a downscale stratified turbulence energy cascade in agreement with previous results. We show that with increasing horizontal resolution, a transition emerges at the buoyancy scale 2 pi U/N, where U is the rms velocity and N is the Brunt-Vaisala frequency. Simulations with high horizontal resolution and isotropic grid spacing exhibit a spectral break at this scale, below which there is a net injection of kinetic energy by nonlinear interactions with the large-scale flow. We argue that these results are consistent with a direct transfer of energy to the buoyancy scale by Kelvin-Helmholtz instability of the large-scale vortices. These findings suggest the existence of a distinct subrange of stratified turbulence between the buoyancy and Ozmidov scales. This range must be at least partially resolved or parameterized to obtain robust simulations of larger-scale turbulence. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3599699]
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