Experimental validation of fluid inertia models for a cylinder settling in a quiescent flow

Abstract

The precise description of the motion of anisotropic particles in a flow rests on the understanding of the force and torque acting on them. Here, we study experimentally small, very elongated particles settling in a fluid at small Reynolds number. In our experiments, we can, to a very good approximation, relate the rate of rotation of cylindrical tungsten rods, of aspect ratios β= 8 and β= 16, settling in pure glycerol to the torque they are experiencing. This allows us to compare the measured torque with expressions obtained either in the slender-rod limit, or in the case of spheroids. Both theories predict a simple angle dependence for the torque, which is found to capture very well the experimental results. Surprisingly, the slender-rod approximation predicts much better the results for β= 8, than for β= 16. In the latter case, the expression obtained for a spheroid provides a better approximation. The translational dynamics is shown to be in qualitative agreement with the slender-rod and spheroid models, the former one being found to represent better the experimental data.

15 pages, 7 figures

References in corpus (3)

• Rotation of a spheroid in a simple shear at small Reynolds number
• Effect of particle inertia on the alignment of small ice crystals in turbulent clouds
• Flow structure and loads over inclined cylindrical rodlike particles and fibers

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• Torques on curved atmospheric fibres
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• Inertial torque on a squirmer