67th Annual Meeting of the APS Division of Fluid Dynamics (November 23, 2014 — November 25, 2014)

P0061: Experiments with heavy particles in a viscous fluid: amazing oscillations

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Authors

• Jakub Nowakowski, Institute of Fundamental Technological Research, Polish Academy of Sciences, Warsaw, Poland
• Maria L. Ekiel-Jezewska, Institute of Fundamental Technological Research, Polish Academy of Sciences, Warsaw, Poland

DOI: https://doi.org/10.1103/APS.DFD.2014.GFM.P0061

Do you want to entertain your kids during breakfast on Sunday?

Take a very high jar of liquid honey and a number of small identical spherical beads, e. g. millimeter steel balls from a ball bearing. Prepare the beads before starting: mix them with a small amount of honey. Next, take into your fingers a triplet of the beads ‘glued’ by the sticky liquid. Try to keep them as close to each other as possible and in a vertical plane, put above the open jar and then release and let them fall into honey. Guess what will you see?

Dancing beads, which try to oscillate periodically while falling in a viscous fluid

The poster shows subsequent configurations of beads settling in honey (left), in silicon oil (middle) and in a viscous fluid, which moves according to the Stokes equations (right). Gravity points down. In observations (left), experiments (middle) and theory (right), a similar evolution of the beads’ relative positions takes place. The configurations at time T/6 are almost the mirror images of the ones at time equal zero (the mirror is vertical), except a permutation of particles. Therefore, periodic motions with the period T exist. In experiments, they are unstable and usually break up after a bit longer than 1/6 of the period. Right panel is reproduced with permission from M. L. Ekiel-Jezewska, T. Gubiec, P. Szymczak, Stokesian dynamics of close particles, Phys. Fluids, 20, 063102 (2008). Copyright 2008. AIP Publishing LLC.