TY - JOUR
T1 - Settling of nonuniform cylinders at intermediate Reynolds numbers
AU - Angle, Brandon R.
AU - Rau, Matthew J.
AU - Byron, Margaret L.
N1 - Publisher Copyright:
© 2024 American Physical Society.
PY - 2024/7
Y1 - 2024/7
N2 - Many natural and industrial processes involve the sedimentation of nonspherical particles. Many of these particles do not have uniform mass distributions; two cases of interest are aggregates (which may be composed of multiple materials) and microplastic pollutants (which may experience localized fouling or degradation). For such particles, the centers of mass and buoyancy are not colocated. This leads to interesting settling dynamics, particularly at transition points near the onset of wake instabilities. We investigated the orientation and terminal velocity of initially horizontal, freely falling cylinders, in which the mass distribution was either constant (uniform density) or bipartite, undergoing a step change halfway along the length (compound density). Cylinders had low aspect ratios (1≤AR≤4) and fell at intermediate Reynolds numbers (around 200). We recorded the position and orientation of each cylinder as it fell through still water, as well as the distribution of landing sites. We also performed planar particle image velocimetry to visualize wake dynamics. Results showed significant differences in the settling characteristics of uniform- vs compound-density cylinders, and revealed three distinct settling modes: rectilinear, oscillatory, and oblique. Each of the three modes displayed distinctly different wakes and vortex shedding patterns. All compound density cylinders, regardless of aspect ratio, were biased to land on the side of the tank, where the more dense end of the cylinder was initially oriented. Our results show that the interplay between buoyant torques and wake instability strongly impacts particle motion in the context of still-water settling, and is likely to play a role in more complex flows. This is true even for particles with an extremely small offset between the center of mass and the center of buoyancy, carrying strong implications for the dispersion of relevant particle classes such as microplastics.
AB - Many natural and industrial processes involve the sedimentation of nonspherical particles. Many of these particles do not have uniform mass distributions; two cases of interest are aggregates (which may be composed of multiple materials) and microplastic pollutants (which may experience localized fouling or degradation). For such particles, the centers of mass and buoyancy are not colocated. This leads to interesting settling dynamics, particularly at transition points near the onset of wake instabilities. We investigated the orientation and terminal velocity of initially horizontal, freely falling cylinders, in which the mass distribution was either constant (uniform density) or bipartite, undergoing a step change halfway along the length (compound density). Cylinders had low aspect ratios (1≤AR≤4) and fell at intermediate Reynolds numbers (around 200). We recorded the position and orientation of each cylinder as it fell through still water, as well as the distribution of landing sites. We also performed planar particle image velocimetry to visualize wake dynamics. Results showed significant differences in the settling characteristics of uniform- vs compound-density cylinders, and revealed three distinct settling modes: rectilinear, oscillatory, and oblique. Each of the three modes displayed distinctly different wakes and vortex shedding patterns. All compound density cylinders, regardless of aspect ratio, were biased to land on the side of the tank, where the more dense end of the cylinder was initially oriented. Our results show that the interplay between buoyant torques and wake instability strongly impacts particle motion in the context of still-water settling, and is likely to play a role in more complex flows. This is true even for particles with an extremely small offset between the center of mass and the center of buoyancy, carrying strong implications for the dispersion of relevant particle classes such as microplastics.
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U2 - 10.1103/PhysRevFluids.9.070501
DO - 10.1103/PhysRevFluids.9.070501
M3 - Article
AN - SCOPUS:85197644912
SN - 2469-990X
VL - 9
JO - Physical Review Fluids
JF - Physical Review Fluids
IS - 7
M1 - 070501
ER -