Barchan-barchan dune repulsion investigated at the grain scale

TL;DR

This study uses grain-scale numerical simulations to investigate the fluid and granular interactions responsible for the repulsion between barchan dunes, revealing how flow disturbance and erosion influence dune dynamics on Earth and Mars.

Contribution

It provides a detailed grain-scale analysis of barchan-barchan interactions, specifically explaining the mechanisms behind dune repulsion and differential shrinkage.

Findings

Downstream barchan shrinks faster due to flow disturbance.

Flow induces higher erosion on the downstream dune.

Upstream dune maintains higher velocity despite wake effects.

Abstract

Barchans are eolian dunes of crescent shape found on Earth, Mars and other celestial bodies. Among the different types of barchan-barchan interaction, there is one, known as chasing, in which the dunes remain close but without touching each other. In this paper, we investigate the origins of this barchan-barchan dune repulsion by carrying out grain-scale numerical computations in which a pair of granular heaps is deformed by the fluid flow into barchan dunes that interact with each other. In our simulations, data such as position, velocity and resultant force are computed for each individual particle at each time step, allowing us to measure details of both the fluid and grains that explain the repulsion. We show the trajectories of grains, time-average resultant forces, and mass balances for each dune, and that the downstream barchan shrinks faster than the upstream one, keeping, thus, a relatively high velocity although in the wake of the upstream barchan. In its turn, this fast shrinkage is caused by the flow disturbance, which induces higher erosion on the downstream barchan and its circumvention by grains leaving the upstream dune. Our results help explaining the mechanisms behind the distribution of barchans in dune fields found on Earth and Mars.