Wind-blown sand: transport rates from saltation to sheet flow
Abstract: Steady states of aeolian sediment transport were calculated numerically using two complementary approaches: (a) for strong winds, where in-flight collisions between particles dominates, the equations for collisional sheet flow were integrated, complemented with an erodible bottom boundary condition (Jenkins and Askari, J. Fluid Mech. vol 223, p. 497, 1991) and approximate collisionless boundary conditions at the top. In this scheme, the flow thickness is found as an eigenvalue of the system of equations; (b) for softer winds, the collisionless Boltzmann equation, coupled with a splash function, was solved. For case (a) the boundary conditions are unable to sustain the flow when the wind is not strong enough. Also the approximations made in the top boundary conditions limit the applicability of the numerical solution for strong winds. For case (b) the dependence of the total mass transport rate on the wind strength is affected by the choice of splash function, in particular b! y the scaling of the average vertical ejection velocity of the splashed particles on impact speed.