Prediction of natural mixing in tightly packed 7-rod-bundles (p/d = 1.10)

The predicted fine structure of flow within a 7-rod-bundle at fixed rod-to-rod gap distance (p/d = 1.1) and at different rod bundle-to-wall distances are presented (NRe = 105; NPr ≅ 1.0). The numerical code VANTACY-II has been used to calculate the single phase, fully developed turbulent flow conditions in arbitrary 2-dimensional solution domains. The code includes a model of anisotropic turbulent exchange appropriate for tight lattices. The different rod-bundle boundary structures effect the fluid flow conditions, although the influence of the hydraulics on the temperature field is partly compensated by the turbulent microconvective heat transport between central and wall subchannels. In other words, the turbulent mixing depends to a great extent on the size and on the wetted perimeter of the edge region. (orig./DG)