Direct numerical simulations of aeolian sand ripples

Abstract

Aeolian sand beds exhibit regular patterns of ripples resulting from the interaction between topography and sediment transport. Their characteristics have been so far related to reptation transport caused by the impacts on the ground of grains entrained by the wind into saltation. By means of direct numerical simulations of grains interacting with a wind flow, we show that the instability turns out to be driven by resonant grain trajectories, whose length is close to a ripple wavelength and whose splash leads to a mass displacement towards the ripple crests. The pattern selection results from a compromise between this destabilizing mechanism and a diffusive downslope transport which stabilizes small wavelengths. The initial wavelength is set by the ratio of the sediment flux and the erosion/deposition rate, a ratio which increases linearly with the wind velocity. We show that this scaling law, in agreement with experiments, originates from an interfacial layer separating the saltation zone from the static sand bed, where momentum transfers are dominated by mid-air collisions. Finally, we provide quantitative support for the use the propagation of these ripples as a proxy for remote measurements of sediment transport.

21 pages, 12 figures

References in corpus (2)

• A scaling law for aeolian dunes on Mars, Venus, Earth, and for subaqueous ripples
• Aeolian sans ripples: experimental study of saturated states

Cited by in corpus (11)

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• Aeolian sand transport: Scaling of mean saltation length and height and implications for mass flux scaling
• Coevolving aerodynamic and impact ripples on Earth
• The fluctuation energy balance in non-suspended fluid-mediated particle transport
• Large Effects of Particle Size Heterogeneity on Dynamic Saltation Threshold
• Scaling laws for planetary sediment transport from DEM-RANS numerical simulations
• Emergence of wind ripples controlled by mechanics of grain-bed impacts
• Quantifying the form-flow-saltation dynamics of aeolian sand ripples
• Modeling the dynamics of aeolian meter-scale bedforms induced by bed heterogeneities