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arXiv · 1606.07329

Columnar structure formation of a dilute suspension of settling spherical particles in a quiescent fluid

Sander G. Huisman·Thomas Barois·Mickaël Bourgoin·Agathe Chouippe·Todor Doychev·Peter Huck·Carla E. Bello Morales·Markus Uhlmann·Romain Volk
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Abstract

The settling of heavy spherical particles in a column of quiescent fluid is investigated. The performed experiments cover a range of Galileo numbers ($110 \leq \text{Ga} \leq 310$) for a fixed density ratio of $Γ= ρ_p/ρ_f = 2.5$. In this regime the particles are known (M. Jenny, J. Dušek and G. Bouchet, Journal of Fluid Mechanics 508, 201 (2004).) to show a variety of motions. It is known that the wake undergoes several transitions for increasing $\text{Ga}$ resulting in particle motions that are successively: vertical, oblique, oblique oscillating, and finally chaotic. Not only does this change the trajectory of single, isolated, settling particles, but it also changes the dynamics of a swarm of particles as collective effects become important even for dilute suspensions, with volume fraction up to $Φ_V = \mathcal{O}\left(10^{-3}\right)$, which are investigated in this work. Multi-camera recordings of settling particles are recorded and tracked over time in 3 dimensions. A variety of analysis are performed and show a strong clustering behavior. The distribution of the cell areas of the Voronoï tessellation in the horizontal plane are compared to that of a random distribution of particles and shows clear clustering. Moreover, a negative correlation was found between the Voronoï area and the particle velocity; clustered particles fall faster. In addition, the angle between two adjacent particles and the vertical is calculated and compared to a homogeneous distribution of particles, clear evidence of vertical alignment of particles is found. The experimental findings are compared to simulations.

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Sander G. Huisman, Thomas Barois, Mickaël Bourgoin, Agathe Chouippe, Todor Doychev, Peter Huck, Carla E. Bello Morales, Markus Uhlmann, Romain Volk. 2016-11-17. Columnar structure formation of a dilute suspension of settling spherical particles in a quiescent fluid. https://doi.org/10.1103/physrevfluids.1.074204

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