LES of stratified turbulent shear flows at moderate to high Reynolds number

A large-eddy simulation (LES) model is used to study the evolution of stratified turbulence in two canonical problems: a temporally evolving shear layer and a spatially evolving wake. The presented LES model is adapted from that of Ducros et al. (1996). In the simulation of the shear layer at Reynolds number, Re = ΔUδ_ω/ν = 5,000, and bulk Richardson number, Ri_b = gΔρδ_ω/ρ₀ΔU² = 0.1, the LES model successfully captures the evolution of Kelvin-Helmholtz rollers, the pairing of the rollers, and the generation of three-dimensional turbulence. The evolution of the momentum and density thickness, turbulent kinetic budget, and energy spectrum show excellent agreement with comparable direct numerical simulations (DNS). Simulations with the subgrid model at a high Re = 50,000 also yield good results. The LES model is also employed in the study of a spatially evolving wake at Re = U_∞D/ν = 3,700 and Froude number, Fr = U_∞/ND = 3, to demonstrate its ability to capture the development of coherent wake vortices, the evolution of wake dimensions, and defect velocity decay when compared to DNS results. We will also discuss the capability of the LES to simulate wakes at high Re and Fr.