CFD Analysis of Cross Flow in Rod Bundles Under Rolling Motion

A CFD analysis of cross flow in rod bundles in rolling motion was performed to investigate the effect of rolling motion on the flow behavior between the subchannels. The rolling motion was assumed as a sinusoid. The additional forces due to the rolling motion including azimuthal force, centrifugal force and coriolis force were added into the source term in the momentum equation. A transient three dimensional simulation of square rod bundles model was performed in various rolling conditions. In order to precisely predict secondary flow patterns in rod bundles, Reynolds Stress Model was selected as the turbulent model. Effect of various rolling parameters such as rolling velocity and amplitude on the cross mixing was investigated. The results show that cross flow is strongly affected by the rolling motion. The local cross flow field in rolling motion was showed in detail. Also, the mixing coefficients based on CFD results were calculated. Empirical correlations of turbulent mixing were modified to consider the effect of rolling conditions, which can be used in the traditional subchannel thermal hydraulic code.