Regularization and eddy-viscosity sub-grid scale (SGS) models for large eddy simulations (LES) of stably-stratified flows

Stratified flows involve a density variation in the vertical direction, and have wide applications in many of the phenomena occurring in a variety of geophysical flows. Regularization-based sub-grid scale (SGS) models such as Leray-α, LANS-α and Clark-α models and eddy viscosity-types approaches such as non-dynamic and dynamic Smagorinsky models are assessed through comparisons with direct numerical simulations (DNS) of a Taylor-Green vortex problem in a stably stratified Boussinesq fluid from Rahimi and Chandy, J. Turbulence, 2015. 128³ LES calculations are presented for a Froude number, Fr, of 1 and a Reynolds number, Re, of 1600, using a fast Fourier transform (FFT)-based pseudo-spectral methodology formulated for triple-periodic domains. Features investigated include temporal variations of the energy spectrum cascade, turbulent kinetic and potential energies, local Froude numbers, enstrophy, vertical shearing of the velocities, and dissipation of kinetic and potential energy. The results from these computations demonstrated the capability of LES to effectively predict the cascade of energy for high-Re and suppression of vertical motion under stratification. They also showed the eddy-viscosity-based models performing better in comparison to regularization models.