Direct and large-eddy simulations of a pure thermal plume

A turbulent natural convection flow (Gr=2.2x10(10)) arising from a heated and finite size source in a quiescent and infinite environment was numerically investigated by means of direct numerical simulation (DNS) and large eddy simulation. Several subgrid-scale models (SGS) were tested and specific attention was paid to dynamic models. The well known dynamic model was compared to the Lagrangian dynamic model which was applied to both dynamic coefficient and turbulent Prandtl number. DNS results show good agreement with experimental results while the Lagrangian dynamic model and especially the extended Lagrangian dynamic model to Prandtl number estimation were found to significantly improve the prediction of pure thermal plume evolution, especially in the turbulent region in which the main turbulent characteristics fitted DNS results. The puffing phenomenon, i.e., unsteady vortex shedding concentration that occurs in the very close vicinity of the finite size source, was not correctly predicted by SGS models but only required sufficient grid resolution. (c) 2007 American Institute of Physics.