Large eddy simulation of turbulent thermal convection using a mixed scale diffusivity model

The Mixed Scale Diffusivity Model, originally developed in the case of the differentially heated cavity, is applied to compute turbulent Rayleigh-Benard flow in an infinite fluid layer at Pr = 0.71 For a large range of Rayleigh numbers (6.3 x 10(5)-2 x 10(11)). The effect of this SGS modelling, which adjusts locally the SGS diffusivity to the thermal scales of the flow and results in variable Pr-SGS like the dynamic approach, is emphasised by comparison with LES and TRANS literature data. A single scaling regime is found in a range of Rayleigh numbers 6.3 x 10(5) - 2 x 10(10), whose properties include the Ra-0.302 scaling law for the Nusselt number and for the thermal boundary layer thickness, in agreement with the experimental correlation of Niemela et al. (2000). The first indication of a transition towards a new regime appears above Ra = 10(11).