EVALUATION OF A FOUR PARAMETER HEAT TRANSFER TURBULENCE MODEL FORCED LBE FLOWS IN DIFFERENT GEOMETRIES.

The present work addresses an effort to improve the prediction of turbulent heat transfer for LBE coolant flows in plane, simple cylindrical rod and bundle rod geometries. In particular the simulations aim to reproduce fully developed thermal and velocity profiles by using a standard finite element implementation of the Navier Stokes equations coupled with the energy and momentum turbulence models. κ-ε system with low-Reynolds model functions is employed in order to compute the turbulent flow with a near-wall approach. The turbulent heat flux is approximated by an isotropic diffusion gradient model where its eddy diffusivity αt is a function of the ratio R between the temperature and velocity turbulent time scales. In order to compute the turbulent time scale of temperature two new variables are defined, the mean square temperature fluctuation κθ and its dissipation εθ , which are calculated by solving two transport equations. Results obtained from the four parameter κ-ε-κθ -εθ model are compared with DNS data available in literature for plane and cylindrical geometries. Finally forced fully developed flows in cylindrical rod and bundle rod geometry are compared with heat transfer correlations extracted by experimental data.