Numerical study on mixing of oscillating quasi-planar jets with low Reynolds number turbulent stress and heat flux equation models

A comparative investigation was conducted on the mechanistic numerical simulation of mixing of non-isothermal, quasi-planar jets incorporating low Reynolds number turbulent stress and heat flux equation models (LRSFM) and an experiment. A water test facility with three vertical jets, the unheated in between two heated jets, simulated convective mixing and temperature fluctuations expected at the outlet of a liquid metal fast reactor core. The LRSFM and a two-equation k-epsilon turbulence model were applied to the simulation. The LRSFM showed good agreement with the experiment, with respect to mean profiles and reproduced the oscillatory motion of the jetting flow, while the k-epsilon model under-predicted the mixing effect, such that a transverse mean temperature difference remained well downstream. Specifically the LRSFM results indicated that the influence of turbulence on mixing was of second order importance in the present flow, while the contribution by coherent phenomena, mainly associated with the periodic oscillation of the present jets, promoted the mixing. These results were evident in both the numerical simulation with LRSFM and in the experiment.