Density stratification has a strong impact on turbulence in geophysical flows. Stratification changes the spatial turbulence spectrum and the energy transport and conversion within the spectrum. We analyze these effects based on a series of direct numerical simulations (DNS) of stratified turbulence. To facilitate simulations of real-world problems, which are usually beyond the reach of DNS, we propose a subgrid-scale turbulence model for large eddy simulations of stratified flows based on the Adaptive Local Deconvolution Method (ALDM). Flow spectra and integral quantities predicted by ALDM are in excellent agreement with direct numerical simulation. ALDM automatically adapts to strongly anisotropic turbulence and is thus a suitable tool for studying turbulent flow phenomena in atmosphere and ocean.

In order to evaluate turbulence subgrid-scale models for stably stratified flows, we performed direct numerical simulations (DNS) of homogeneous stratified turbulence with large-scale horizontal forcing. In these simulations we found that energy dissipation is concentrated within thin layers of horizontal tagliatelle-like vortex sheets between large pancake-like structures. For large eddy simulation (LES), we use an implicit subgrid-scale model, based on the Adaptive Local Deconvolution Method (ALDM). Our analysis proves that the implicit turbulence model ALDM correctly predicts the turbulence energy budget and the energy spectra of stratified turbulence, even though dissipative structures are not resolved on the computational grid.

In order to evaluate turbulence subgrid-scale models for stably stratified flows, we performed direct numerical simulations (DNS) of homogeneous stratified turbulence with large-scale horizontal forcing. In these simulations we found that energy dissipation is concentrated within thin layers of horizontal tagliatelle-like vortex sheets between large pancake-like structures. For large eddy simulation (LES), we use an implicit subgrid-scale model, based on the Adaptive Local Deconvolution Method (ALDM). Our analysis proves that the implicit turbulence modelALDMcorrectly predicts the turbulence energy budget and the energy spectra of stratified turbulence, even though dissipative structures are not resolved on the computational grid.

The analysis of the spectral eddy viscosity is a handy tool to analyze the performance of LES methods. It reflects the cumulated effect of numerical discretization and turbulence subgrid-scale model on the spectral energy transfer. We compute this quantity by filtering and truncating data from direct numerical simulations of neutrally and stably stratified homogeneous turbulence. The results are used for testing of implicit and explicit LES methods. We find indications that for stably stratified turbulence it is necessary to use different subgrid-scale models for the horizontal and vertical velocity components.

Simulations of geophysical turbulent flows require a robust and accurate subgrid-scale turbulence modeling. To evaluate turbulence models for stably stratified flows, we performed direct numerical simulations (DNSs) of the transition of the three-dimensional Taylor-Green vortex and of homogeneous stratified turbulence with large-scale horizontal forcing. In these simulations we found that energy dissipation is concentrated within thin layers of horizontal tagliatelle-like vortex sheets between large pancake-like structures. We propose a new implicit subgrid-scale model for stratified fluids, based on the Adaptive Local Deconvolution Method (ALDM). Our analysis proves that the implicit turbulence model ALDM correctly predicts the turbulence energy budget and the energy spectra of stratified turbulence, even though dissipative structures are not resolved on the computational grid.