A thermal-hydraulic field analysis code using the finite element method is developed to analyze the effects of anisotropic turbulent diffusion and secondary flow on turbulent mixing, which is essential to the nuclear fuel performance analysis.

In this study a new model of anisotropic eddy viscosity is developed. The representative value of the anisotropic factor is determined from the scale relation that is derived on the basis of the flow pulsation phenomenon. The spatial distribution is deduced qualitatively from well-known experiments. The flow fields calculated by this code are compared with experimental data and show good agreements, and the predicted turbulent mixing rates are successfully compared with the scale relation derived in the authors' previous work.

The results show that the isotropic eddy viscosity model underestimates the mixing rate and gives the reverse trend as the gap size reduces, and the secondary flow has a minor effect compared with the anisotropic eddy viscosity in the turbulent mixing process. Although the mixing phenomenon of the flow pulsation is a convective process, it can be simulated only by the anisotropic model.