Author(s): Albert Gyr; Andreas Miiller; Arnold Schmid
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Abstract: Sand grains on a hydraulically smooth river bed, made up of uniform particles, were observed to rearrange into stable configurations due to sediment transport. This occurs if on an initially flattened bed the shear stress is slightly increased above its critical value for incipient motion. If the wall shear stress is further increased, an intermittent transport in streaky form occurs and a second stable configuration of another kind with an arrow shape bed form appears. The transport then remains constant even if the wall shear stress is slightly increased again. Both stable forms show a definitely higher friction factor than the intermittent transport. These processes are explained by making use of the concept of coherent structures for the turbulent flow.
Year: 1989