
The dependence of the Nusselt number Nu on the Rayleigh Ra and Prandtl Pr number is determined for 104 < Ra < 107 and 0.07 < Pr < 7 using DNS with no-slip upper and lower boundaries and free-slip sidewalls in a 8 × 8 × 2 box. Nusselt numbers, velocity scales and boundary layer thicknesses are calculated. For Nu there are good comparisons with experimental data and scaling laws for all the cases, including Ra2/7 laws at Pr = 0.7 and Pr = 7 and at low Pr, a Ra1/4 regime. Calculations at Pr = 0.3 predict a new Nu ∼ Ra2/7 regime at slightly higher Ra than the Pr = 0.07 calculations reported here and the mercury Pr = 0.025 experiments.
velocity scales, Prandtl number, Direct numerical and large eddy simulation of turbulence, Heat and mass transfer, heat flow, Rayleigh number, Shear flows and turbulence, Nusselt number, boundary layer thicknesses, Boussinesq approximation
velocity scales, Prandtl number, Direct numerical and large eddy simulation of turbulence, Heat and mass transfer, heat flow, Rayleigh number, Shear flows and turbulence, Nusselt number, boundary layer thicknesses, Boussinesq approximation
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