Abstract
Particle-resolved direct numerical simulations of monodisperse settling suspensions of cubes and spheres are performed for Galileo numbers and , and solid volume fractions in the range . The solid-to-fluid density ratio is taken to be fixed at 2, representing liquid-solid suspensions. Strong columnar clustering is observed for and in a sphere suspension, whereas similar vertical structures are not present as prominently in a cube suspension. We find that in all cases, cube suspensions tend to be more homogeneous compared to sphere suspensions, as indicated by both their microstructure and momentum transfer properties. The enhanced homogeneity is associated with the pronounced angular velocities of cubes and the resulting orientation- and rotation-induced lift forces, which promote transverse motions and the likelihood of escaping from clusters. Higher rotation rates of cubes thus play a major role in the transfer of momentum from the gravity to the transverse direction, demonstrated by the lower anisotropy of particle velocity fluctuations in cube suspensions. In more dilute cases, cubes induce significantly stronger pseudoturbulence in the flow, especially in the transverse direction. The drag of dynamic cube suspensions is found to be generally similar to static beds of cubes, the reason for which is speculated to be relevant to their motion freedom and the more homogeneous microstructure.
7 More- Received 24 October 2020
- Accepted 9 March 2021
DOI:https://doi.org/10.1103/PhysRevFluids.6.044306
©2021 American Physical Society
Physics Subject Headings (PhySH)
synopsis
Cubes Keep Their Distance
Published 21 April 2021
Cubes suspended in a liquid are less likely than spheres to form clusters and fall out of solution.
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