Numerical simulation of turbulent flow and mixing in a rod bundle geometry

摘要

This paper presents a numerical simulation of turbulent flow and heat transfer in a rod bundle geometry for investigation of turbulent interchange mixing between subchannels. The Reynolds stress model (Launder, Reece, and Rodi model) and the k-ε turbulence model were used, while the turbulent heat flux was modelled using the eddy heat flux concept. Three secondary flow circulation loops in a subchannel were predicted by the Reynolds stress model, and the maximum magnitude of the secondary velocities was about 1·2% of the mean axial velocity. As expected, the k-ε model was unable to predict secondary flows. From the comparison with experimental results, it was found that both models underpredicted maximum circumferential turbulence intensities near the gaps, overpredicted temperature gradients near the gap, and underpredicted the gap Stanton number (which is a measure of mixing). The discrepancy of the predictions is caused by the inability of the turbulence models to account for flow pulsations which are likely driven by large eddy motions. It was found that the contribution of flow pulsation increased with decreased gap spacing, while the contribution of secondary flows is relatively small.