Reprint of: Rod bundle vortex networks, gap vortex streets, and gap instability: A nomenclature and some comments on available methodologies

This note introduces the following terms, which apply to large-scale, vortical, coherent structures, appearing in flows through tightly packed rod bundles and other channels that have narrow gap regions: the term gap instability describes the mechanism of generation of such structures in the gap region in laminar and turbulent flows; the term gap vortex street describes the chain of counter-rotating vortices which from on either side of a single gap; and the term rod bundle vortex network describes the set of mutually dependent gap vortex streets that appear in rod bundles and other channels with multiple gaps. Moreover, this notes summarizes the capabilities and limitations of available CFD methods for simulating flows in rod bundles.