Hartke, G.J., V.M. Canuto, and W.P. Dannevik, 1988: A direct interaction approximation treatment of high Rayleigh number convective turbulence and comparison with experiment. Phys. Fluids, 31, 256-262, doi:10.1063/1.866856.
Recently published experimental results [Int. J. Heat Mass Transfer, 23, 738 (1980)] on thermally driven high Rayleigh number turbulent convection have shown that the N proportional to R(2/7) relation (where N is the Nusselt number and R is the Rayleigh number), which is valid up to R ≈ 5×108, is superceded at this point by the relation N = Aσ*R(1/3) that holds at least up to R ≈ 1011. For water (Prandtl number σ = 6.6), the experimental value for Aσ was found to be Aσ = 0.0556±0.001. In the present work, the equations for a turbulent fluid driven by thermal convection are solved using the two-point closure prescription of the direct interaction approximation. The theoretical N vs R relation at high R is found to be of the form N = Aσ*R(1/3) and for σ = 6.6, and the predicted value of the coefficient Aσ is computed to be Aσ ≲ 0.08, in good agreement with the experimental value. Extension of the model to situations other than convection is discussed.