Simulation of aerodynamic entrainment with interparticle cohesions based on discrete element method

Abstract

Aerodynamic entrainment acts as the pioneer of saltation movement and is critical for understanding the development of aeolian phenomena. In this study, air‐driven particles whose bottoms have left the bed surface were considered to be entrainment particles; this definition differs from the previous definition considering the initiation of rolling. We simulated the aerodynamic lifting of surface particles on a randomly oriented sedimentary bed using the discrete element method (DEM); we also proved that particles do not leave the bed vertically with speeds equal to the speed required to reach the height of one grain diameter, as is widely accepted. Rather, the particles were found to leave the bed at a much smaller angle and with much larger velocities with respect to the bed surface. The rate of entrainment exhibits an approximately linear dependence on the shear velocity, not a quadratic dependence, because the velocity of the entrained particles increases linearly with shear velocity. Moreover, the interparticle cohesion, which was found to increase the fluid entrainment threshold significantly, had no effect on the entrainment rate or on the take‐off velocity and angular distributions of the entrained particles. This is because the collisions between the entrained and bed particles destroy the interparticle bonds. Herein, we summarize a complete entrainment scheme based on DEM simulations, which provides a new approach for exploring the development and evolution of aeolian transportation processes.

Aeolian sand transport: Scaling of mean saltation length and height and implications for mass flux scaling

“…One such potential problem was pointed out by Pähtz and Durán (2018) and : Even if a grain initially escapes the bed surface pocket in which it is resting, it will still be quickly captured by the bed if it, on average, loses more energy in its subsequent impact(s) on the bed than it gains during its subsequent saltation hop(s) through wind drag acceleration (i.e., if the grain is net decelerated). In other words, grains should only be considered as leaving the bed if they are net accelerated after escaping their bed surface pocket (note that a similar definition was recently also applied to aerodynamic entrainment, Jia and Wang, 2021). The analytical saltation model of Pähtz et al (2021) therefore only considers rebounding grains in the modeling of the replacement capacity condition.…”

Impact of turbulence on aeolian particle entrainment: results from wind-tunnel experiments

“…Our question here is how turbulence influences aeolian processes, especially the entrainment of sand and dust parti-cles into the atmosphere. Numerous studies on aerodynamic sand and dust entrainment have been carried out (e.g., Greeley and Iversen, 1987;Haff, 1988, 1991;Loosmore and Hunt, 2000;Doorschot and Lehning, 2002;Jia and Wang, 2021), but in most of these studies, flow is assumed to be steady, and the effect of turbulence on the entrainment is not accounted for. In reality, the flows and flow-driven aeolian processes are both impossible to stabilize.…”