Three-dimensional numerical simulations of barchan dune interactions in unidirectional flow

In this study, a constitutive model based on fluvial hydrodynamics is coupled with a large eddy simulation to better understand barchan dune interactions from the perspective of morphological dynamics. The results show that the developed model can reproduce crescent-shaped dunes, as well as variations in turbulent flow structures above the dune surface. The interactions between two barchan dunes arranged in coaxial and staggered alignments are simulated by changes in their initial mass ratios. A critical moment of fast erosion is observed for the larger of the two coaxial dunes, and the value of this moment converges to a constant with a linear increase in the mass ratio. The interaction pattern of ?coalescence? agrees with that of the experiments. These results provide deep insights into the transition of the barchan dune interaction patterns from ?coalescence? to ?ejection?, which corresponds to a dynamic mass equilibrium state in large dunes. In addition, one elongated horn created from merged barchans after a staggered collision reaffirms that dune collision and influx asymmetry are two potential mechanisms in barchan asymmetry.