In Physics of Fluids, researchers have been studying the dynamics of how crescent-shaped sand dunes are formed. Known as barchans, these formations are commonly found in various sizes and circumstances, on Earth and on Mars. Using a computational fluid dynamics approach, the team carried out simulations by applying the equations of motion to each grain in a pile being deformed by a fluid flow, showing the ranges of values for the proper computation of barchan dunes down to the grain scale.