Europhys. Lett.
Volume 65, Number 1, January 2004
Page(s) 13 - 19
Section General
Published online 01 December 2003
Europhys. Lett., 65 (1) , pp. 13-19 (2004)
DOI: 10.1209/epl/i2003-10045-y

Origin of non-Gaussian velocity distributions in steady-state sedimentation

E. Kuusela1, J. M. Lahtinen1 and T. Ala-Nissila1, 2

1  Laboratory of Physics, Helsinki University of Technology P.O. Box 1100, FIN-02015 HUT, Espoo, Finland
2  Department of Physics, Brown University - Providence, RI 02912-1843, USA

(Received 17 July 2003; accepted in final form 15 October 2003)

We study the settling dynamics of non-Brownian particles during steady-state sedimentation under realistic conditions by computer simulations. We show that the velocity fluctuations parallel to gravity change systematically with the particle volume fraction $\Phi$. For dilute systems, their distribution function has a non-Gaussian form, with an extended tail in the direction of the downward velocity, while for dense systems the situation is the opposite. In the intermediate regime at $\Phi\approx 0.05$ the fluctuations are Gaussian. We show that these distributions can be understood from the dependence of the settling velocity and its fluctuations on the local density around each particle.

05.40.-a - Fluctuation phenomena, random processes, noise, and Brownian motion.
47.55.Kf - Multiphase and particle-laden flows.
83.85.Pt - Computational fluid dynamics.

© EDP Sciences 2004