The flow and heat transfer in rod bundles are of vital importance in the reactor design. Studies on the turbulent flow in tight lattice have presented the quasi periodic large scale vortex structure is highly accounted for the local flow and heat transfer and turbulent mixing in rod bundles.
In this work, the Unsteady Reynolds Averaged Navier–Stokes (URANS) simulation with the Reynolds Stress Model (RSM) is adopted to simulate the flow and vortex structure in rod bundles. The vortex structure in sparse lattice with nonuniform wall roughness is also investigated and compared with that in tight lattice. The results indicate that the quasi periodic large scale vortex structure and flow pulsation are available in both tight lattice and the sparse lattice with non-uniform wall roughness. Due to the existence of the vortex structure, the heat transfer in spare lattice is enhanced.