Ripple formation in weakly turbulent flow |
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Authors: | A Wierschem C Groh I Rehberg N Aksel C A Kruelle |
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Institution: | 1.Technische Mechanik und Str?mungsmechanik,Universit?t Bayreuth,Bayreuth,Germany;2.Experimentalphysik V,Universit?t Bayreuth,Bayreuth,Germany |
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Abstract: | The formation of granular ripples under liquid shear flow in an annular channel is studied experimentally. The erodible granular
bed is subject to weakly turbulent flows without a defined sharp boundary layer close to the granular bed. The flow field
and the degree of turbulence is characterized quantitatively by using a particle image velocimeter and a laser-Doppler velocimeter,
respectively. A new range of particle Reynolds numbers at the lower limit of the Shields diagram were explored. Quantitative
measurements of the granular flow on the surface reveal that the threshold for particle motion coincides within the order
of one percent with the threshold for ripple formation. In fully developed ripples it was found that on the leeward side of
the ripples regions of low-velocity gradients exist where granular motion is scarce, indicating that the coupling between
the ripples is mainly caused by the flow field of the liquid. |
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Keywords: | 45 70 -n Granular systems 92 10 Wa Sediment transport 92 40 Gc Erosion and sedimentation sediment transport |
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