Study of Aerodynamic Grain Entrainment in Aeolian Transport

• Published in: Geophysical research letters 2020-06, Vol.47 (11), p.n/a
• Main Authors: Li, G., Zhang, J., Herrmann, H. J., Shao, Y., Huang, N.
• Format: Article
• Language: English
• Subjects: aerodynamic entrainment; Aerodynamics; Computational fluid dynamics; Continuous flow; Entrainment; Environmental Engineering; Environmental Sciences; Eolian sands; Eolian transport; Grains; Landforms; Mastering; Particle settling; Saltation; Sand transport; Sediment transport; Shear stress; Soil erosion; Soils; Stress concentration; surface shear stress; Turbulence; Wind measurement; wind tunnel; Wind tunnels
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2019GL086574

Aeolian transport controls landform formations on Earth and other planets and crucially affects the atmospheric system. With elaborate wind tunnel measurements, we find that the aerodynamic entrainment rate follows a yet unreported exponential increase in the intermittent regime and only complies with the expected linear law for the condition of continuous entrainment. Subsequently, we propose a model accounting for the effects of turbulence on aerodynamic entrainment based on the distribution of local shear stress to describe the experimental results. We also provide evidence that aerodynamic entrainment can be an efficient way to directly induce a horizontal grain transport comparable to the steady and saturated saltation in unsaturated conditions and should not be ignored. Our findings substantially modify the present interpretation of surface erosion and bear thus important consequences on future soil protection techniques. Plain Language Summary It has been recognized that grains can be lifted from the surface through two mechanisms, either ejection due to the impact of grains in saltation or the pull‐out of grains due to aerodynamic entrainment. However, saltation has always been believed to be the dominant mechanism of aeolian sand transport. With elaborate wind tunnel measurements, we find that the aerodynamic entrainment rate follows a yet unreported exponential increase in the intermittent regime and only complies with the expected linear law above the threshold to continuous flow. We also present the first evidence that in fact turbulent grain entrainment contributes as least as much to or even more than the particle flux in the continuous flow regime. Our discovery will open a new avenue of research focusing on aerodynamic grain entrainment and thus significantly influence the research of others. It also represents an essential step toward mastering soil erosion. Key Points Two scaling laws are found between aerodynamic entrainment rate of grains and mean surface shear stress in wind tunnel experiments A predictive model considering turbulence is proposed to explain the aerodynamic entrainment rate Aerodynamic entrainment is able to cause streamwise grain flux in unsaturated sand stream