Large eddy simulations of forced and stably stratified turbulence: Evolution, spectra, scaling, structures and shear

Abstract Large eddy simulations (LES) of forced stratified turbulence in a triply-periodic box at multiple Froude numbers ( Fr 0 ) are carried out to study the effect of stratification on energy evolution, spectra, scaling, vortical structures and shear for flows at Re = 25000 . The dynamic Smagorinsky model is used as the sub-grid scale (SGS) closure with a grid density of 96 3 . A three-dimensional (3D) continuous forcing scheme adapted from Rosales et al. (2005), where a constant factor is multiplied to the velocity scales, is applied to LES for the first time in stably-stratified turbulence. Calculations for three different Froude numbers, Fr 0 = 0.1 , 0.2 and 0.3 , are presented here. The behavior of the energy spectra and flux and evolution of local quantities such as buoyancy Reynolds number, Froude number, Richardson number and shear distribution at a fully developed state are analysed in detail. In addition, the 3D isosurfaces and two-dimensional (2D) isocontours of vorticity are presented, which clearly highlight the suppression of turbulence in the vertical direction. Increase in the intensity of stratification, results in a delay in the attainment of a fully-developed state. Moreover, the dissipation rates and enstrophy at the fully developed state are lower for lower Froude numbers. A κ - 3 scaling is observed for the vertical kinetic energy spectra and a κ - 5 3 scaling for the potential energy spectra. For moderate stratification, i.e. at Fr 0 = 0.3 , the scaling results based on the Bolgiano and Obukhov theory are verified here as well.