Dresden 2009 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 28: Pattern formation in colloidal and granular systems II

DY 28.8: Talk

Friday, March 27, 2009, 12:15–12:30, HÜL 386

A new convection scenario in granulates under geometrical restriction — •Frank Rietz and Ralf Stannarius — Universität Magdeburg, FNW, IEP, Abteilung Nichtlineare Phänomene

An experiment is presented that extends the diversity of pattern forming phenomena found in granular media. A flat container (Hele-Shaw cell) is filled with a granular mixture and slowly rotated about its horizontal long axis. The filling fraction is crucial for the observed effects.

At partial filling of the container, the material can be fluidized during rotation and patterns of axially segregated stripes appear which undergo slow coarsening. This effect resembles stripe patterns commonly found in rotating drums.

A novel interesting phenomenon emerges under geometrical restrictions when the container is nearly filled. Although the particles are on the brink of jamming, and their mobility is almost inhibited, we observe regular convection rolls that are accompanied by, and decorated by a conspicuous serpentine segregation pattern. In contrast to the loosely moving beads at partial filling, the particles move in collective clusters. Furthermore the number of convection rolls is long-term stable and only related to the container geometry.

Even though there are some superficial similarities to well known convection rolls in vibrated granular systems, there are striking differences concerning driving forces, segregation patterns, and number of rolls. Our system complements convection phenomena found in agitated granulates and brings up new questions that are discussed in the study. Phys. Rev. Lett. 100, 078002 (2008).