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-Bénard flow in an infinite fluid layer at Pr = 0.71 for a large range of Rayleigh numbers (6.3 × 10 – 2 × 10). The effect of this SGS modelling, which adjusts locally the SGS diffusivity to the thermal scales of the flow and results in variable PrSGS 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 × 10 – 2 × 10, whose properties include the Ra 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.