  Aerodynamic entrainment acts as the pioneer of saltation movement and is
critical for understanding the development of aeolian phenomena. Here we
performed direct numerical simulations on the aerodynamic lifting of surface
particles on a random arranged sediment bed using the discrete element method,
and provided evidence that particles do not leave the bed vertically with
speeds equal to that needed to reach a height of one grain diameter, as people
widely accepted, but with much smaller angles toward the bed surface and much
larger velocities. The entrainment rate does not exhibit a quadratic dependence
with the shear velocity, but a nearly linear one, because the velocity of
entrained particle increases linearly with shear velocity. Moreover,
inter-particle cohesion increases the fluid entrainment threshold
significantly, but has no effect on the entrainment rate, as well as the
take-off velocity and angle distributions of entrained particles, because the
collisions between entrained and bed particles destroy the inter-particle
bonds. The completely entrainment scheme is given, which provides a credible
approach to explore the development and evolution of aeolian transports.
