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.

arXiv comment21 pages, 12 figures

References in corpus (9)

• The physics of wind-blown sand and dust
• A scaling law for aeolian dunes on Mars, Venus, Earth, and for subaqueous ripples
• Numerical simulation of turbulent sediment transport, from bed load to saltation
• Aeolian sans ripples: experimental study of saturated states
• Midair collisions enhance saltation
• Dynamics of aeolian sand ripples
• Nonlinear Dynamics of Aeolian Sand Ripples
• Jump at the onset of saltation
• A two-species continuum model for aeolian sand ripples

Cited by in corpus (19)

• A unified model of ripples and dunes in water and planetary environments
• Formation of sediment patterns in channel flow: minimal unstable systems and their temporal evolution
• Unification of Aeolian and Fluvial Sediment Transport Rate from Granular Physics
• Giant ripples on comet 67P/Churyumov-Gerasimenko sculpted by sunset thermal wind
• The Cessation Threshold of Nonsuspended Sediment Transport Across Aeolian and Fluvial Environments
• A lower-than-expected saltation threshold at Martian pressure and below
• Local Rheology Relation with Variable Yield Stress Ratio across Dry, Wet, Dense, and Dilute Granular Flows
• Fluid forces or impacts: What governs the entrainment of soil particles in sediment transport mediated by a Newtonian fluid?
• Discrete Element Method simulations of the saturation of aeolian sand transport
• Universal friction law at granular solid-gas transition explains scaling of sediment transport load with excess fluid shear stress
• Aeolian sand transport: Scaling of mean saltation length and height and implications for mass flux scaling
• Analytical mesoscale modeling of aeolian sand transport
• Coevolving aerodynamic and impact ripples on Earth
• The fluctuation energy balance in non-suspended fluid-mediated particle transport
• Scaling laws for planetary sediment transport from DEM-RANS numerical simulations
• Large Effects of Particle Size Heterogeneity on Dynamic Saltation Threshold
• 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