The characteristics of pore scale vortical structures observed in moderate Reynolds number flow through mono-disperse packed beds of spheres are examined. Our results come from direct numerical simulations of flow through (ⅰ) a periodic, simple cubic arrangement of 54 spheres, (ⅱ) a wall bounded, close packed arrangement of 216 spheres, and (ⅲ) a realistic randomly packed tube containing 326 spheres with a tube diameter to sphere diameter ratio of 5.96. Pore Reynolds numbers in the steady inertial ( 10 ≤ Re ≤ 200) and unsteady inertial (Re ≈600) regimes are considered. Even at similar Reynolds numbers, the vortical structures observed in flows through these three packings are remarkably different. The interior of the arranged packings are dominated by multi-lobed vortex ring structures which align with the principal axes of the packing. The random packing and the near wall region of the close packed arrangement are dominated by helical vortices, elongated in the mean flow direction. In the simple cubic packing, unsteady flow is marked by periodic vortex shedding which occurs at a single frequency. Conversely, at a similar Reynolds number, the vortical structures in unsteady flow through the random packing oscillate with many characteristic frequencies.
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