Scaling laws for planetary sediment transport from DEM-RANS numerical simulations

We use an established discrete element method (DEM) Reynolds-averaged Navier-Stokes (RANS)-based numerical model to simulate non-suspended sediment transport across conditions encompassing almost seven orders of magnitude in the particle-fluid density ratio s, ranging from subaqueous transport (s = 2.65) to aeolian transport in the highly rarefied atmosphere of Pluto (s = 10(7)), whereas previous DEM-based sediment transport studies did not exceed terrestrial aeolian conditions (s approximate to 2000). Guided by these simulations and by experiments, we semi-empirically derive simple scaling laws for the cessation threshold and rate of equilibrium aeolian transport, both exhibiting a rather unusual s1/3-dependence. They constitute a simple means to make predictions of aeolian processes across a large range of planetary conditions. The derivation consists of a first-principle-based proof of the statement that, under relatively mild assumptions, the cessation threshold physics is controlled by only one dimensionless control parameter, rather than two expected from dimensional analysis. Crucially, unlike existing models, this proof does not resort to coarse-graining the particle phase of the aeolian transport layer above the bed surface. From the pool of existing models, only that by Pahtz et al. (J. Geophys. Res.: Earth, vol. 126, 2021, e2020JF005859) is somewhat consistent with the combined numerical and experimental data. It captures the scaling of the cessation threshold and the s(1/3)-dependence of the transport rate, but fails to capture the latter's superimposed grain size dependence. This hints at a lack of understanding of the transport rate physics and calls for future studies on this issue.

Automated summary

We use a numerical model to simulate non-suspended sediment transport across a wide range of particle-fluid density ratios. Based on simulations and experiments, we derive simple scaling laws for aeolian transport and find that the cessation threshold is controlled by only one dimensionless parameter. Only one existing model is somewhat consistent with the data, but it fails to capture the grain size dependence of the transport rate, indicating a lack of understanding in this area.