Initiation and evolution of current ripples on a flat sand bed under turbulent water flow |
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Authors: | V Langlois A Valance |
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Institution: | (1) School of Physics, Trinity College Dublin, Dublin, Ireland;(2) G.M.C.M., Université Rennes 1, Bat. 11A, 35042 Rennes, France |
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Abstract: | We investigate the formation and dynamics of sand ripples under a turbulent water flow. Our experiments were conducted in
an open flume with spherical glass beads between 100 and 500μm in diameter. The flow Reynolds number is of the order of 10 000
and the particle Reynolds number of the
order of 1 to 10. We study the development of ripples by measuring their
wavelength and amplitude in course of time and investigate the influence of the grain size and the flow properties.
In particular, we demonstrate two different regimes according to the grain size.
For fine grains, a slow coarsening process (i.e., a logarithmic increase of the wavelength and amplitude) takes place,
while for coarser grains, this process occurs at a much faster rate (i.e., with a linear growth) and stops after a finite
time. In the later case, a stable pattern is eventually observed. Besides, we carefully analyze the wavelength of ripples
in the first stages of the instability as a function of the grain size and the shear velocity of the flow, and compare
our results with other available experimental
data and with theoretical predictions based on linear stability analyses. |
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Keywords: | 45 70 -n Granular systems 45 70 Qj Pattern formation 92 10 Wa Sediment transport |
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