In the large-eddy simulation frame for non-isothermal turbulent flow, the M
ixed Scale Model is extended to the subgrid diffusivity, in order to dissoc
iate the computation of subgrid viscosity and diffusivity. The identificati
on of the subgrid thermal dissipation term in the subgrid flux transport eq
uation leads to an algebraic expression of the subgrid diffusivity. This di
ffusive model, as the Smagorinsky one, is weighted by a model based on scal
e similarity. This expression leads to satisfactory results when applied to
a buoyant turbulent pow in a differentially heated cavity. (C) 2000 Academ
ie des sciences/Editions scientifiques et medicales Elsevier SAS.