Berlin 2008 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 19: Granular matter I
DY 19.1: Talk
Wednesday, February 27, 2008, 14:30–14:45, MA 004
Formation of sand ripples in weakly turbulent flows — •Christof Krülle1, Mustapha Rouijaa2, Tobias Edtbauer1,2, and Nuri Aksel2 — 1Experimentalphysik V, Universität Bayreuth, D-95440 Bayreuth — 2Technische Mechanik und Strömungsmechanik, Universität Bayreuth, D-95440 Bayreuth
One of the most fascinating examples of pattern formation in nature are the dunes and ripples formed in sand, caused either by wind or by shear flows in water. Laboratory studies have focused mainly on the surface profile of the granular layer, describing the ripples and their instability in terms of global parameters. Here, we present an experimental study of ripple generation in an annular channel at rather low Reynolds numbers in weakly turbulent flow. We characterize the fluid velocity field at the onset of ripple generation by utilizing a laser doppler anemometer. These experimental studies show that the local rapid increase of velocity fluctuations close to the sandy bottom initiate the motion of particles and thus will finally lead to the formation of ripple patterns with finite amplitude.