Events in Physics

Structure formations of macroscopic spheres in oscillatory fluid flows

Recently there has been a lot of interest in the collective behaviour and pattern formation in granular matter [1], which can be enhanced by the presence of a fluid. We are interested in the fluid-mediated interactions     between macroscopic rigid particles under sinusoidal vibration in a liquid-filled cell. Various patterns and structures in these flows had been reported [2,3] but the exact details remained unknown. At finite Reynolds numbers the oscillatory motion of a rigid object gives a non-zero time-averaged flow, called steady streaming. We have studied pairs of equal-sized spheres which are found to align perpendicular to the direction of oscillation with a well-defined gap between them [4]. Consequently multiple particles form chain patterns aligned across the direction of vibration. These systems have been investigated both in experiment and in simulation. We show that the mechanisms responsible for these effects can be traced to the streaming flows induced by the motion of the solid spheres relative to the fluid [5].

[1] I. S. Aranson and L. S. Tsimring, Reviews of Modern Physics, 78, 641 (2006); [2] R. Wunenburger, V. Carrier and Y. Garrabos, Physics of Fluids, 14, 2350 (2002); [3] G. A. Voth, B. Bigger, M.R. Buckley, W. Losert, M. P. Brenner, H. A. Stone and J. P. Gollub, Phys. Rev.Lett., 8, 234301, (2002); [4] D. Klotsa, M. R. Swift, R. M. Bowley and P. J. King, Phys. Rev. E, 76, 056314 (2007); [5] D. Klotsa, M. R. Swift, R. M. Bowley and P. J. King, Phys. Rev. E, 79, 021302 (2009).