Abstract
Four different models of pressure-concentration-gradient correlations are considered. These models, together with the local equilibrium approximation in the corresponding second-order closure formulation, permit one to determine all the components of the eddy-diffusivity tensor Kij(z) for steady plane-parallel turbulent flows. Computations of the eddy diffusivities Kij are performed for a homogeneous turbulent flow with constant shear and for an atmospheric surface layer (ASL) in neutral stratification. The results obtained by different models differ only slightly and agree satisfactorily with the available experimental data. Characteristics of the diffusion from an instantaneous point source in the neutral atmospheric surface layer are computed from the considered local equilibrium second-order closures and then are compared with the characteristics obtained from two other second-order closures that are not local equilibrium ones. This comparison shows that more complex theories give results that are close to those obtained from the local equilibrium approximation.
Published Version
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