Large-eddy simulations of turbulent thermal convection using renormalized viscosity and thermal diffusivity

In this paper we employ renormalized viscosity and thermal diffusivity to construct a subgrid-scale model for large eddy simulation (LES) of turbulent thermal convection. For LES, we add νrenâΠu1/3(π/Δ)-4/3 to the kinematic viscosity; here Πu is the turbulent kinetic energy flux, and Δ is the grid spacing. We take subgrid thermal diffusivity to be same as the subgrid kinematic viscosity. We performed LES of turbulent thermal convection on a 1283 grid and compare the results with those obtained from direct numerical simulation (DNS) on a 5123 grid. We started the DNS with random initial condition and forked a LES simulation using the large wave number modes of DNS initial condition. Though the Nusselt number is overestimated in LES as compared to that in DNS, there is a good agreement between the LES and DNS results on the evolution of kinetic energy and entropy, spectra and fluxes of velocity and temperature fields, and the isosurfaces of temperature.