Rigid spherical particles in oscillating fluid flows form interesting patterns as a result of fluid mediated interactions. Here, through both experiments and simulations, we show that two spheres under horizontal vibration align themselves at right angles to the oscillation and sit with a gap between them, which scales in a non-classical way with the boundary layer thickness. A large number of spherical particles form strings perpendicular to the direction of oscillation. Investigating the details of the interactions we find that the driving force is the nonlinear hydrodynamic effect of steady streaming. We then design a simple swimmer (two-spheres-and-a-spring) that utilizes steady streaming in order to propel itself and discuss the nature of the transition at the onset of swimming as the Reynolds number gradually increases.

• Publications:

1. Chain formation of spheres in oscillatory fluid flows. D. Klotsa et al. PRE 79, 021302 (2009).

2. The interaction of spheres in oscillatory fluid flows. D. Klotsa et al. PRE 76, 056314 (2007).

3. Video:

4. from Active and Smart Matter conference Syracuse 2016.

5. CSAWW at the University of Michigan.