Effects of Shape and Rotation of Sand Particles in Saltation

Abstract

Eolian sand transport is a typical gas-solid flow process, and saltating sand particles account for 75% of the total sand transported. Sand particles are considered as perfect spheres, and the forces acted on the particles are calculated using concise formulas in almost all wind-sand movement models. In fact, most of sand particles in natural environment are nonspherical and usually rotating while they saltate in the air, and the complicated turbulent gas-solid flow caused by irregular shape and rotation of particles cannot be predicted. In this paper, the microcosmic midair movements of rotating elliptical sand particles are simulated with dynamic grid method, and the interaction between airflow and sand particles is studied. The results show that the trajectory of a rotating elliptical particle is 18.8% higher and 31.8% longer than that of a spherical one and the drag force acted on a rotating elliptical sand particle fluctuates periodically over time. Separating, colliding, and tumbling behaviors are observed during the saltation process of coupled sand particles. Affected by strong interaction between rotating coupled elliptical particles and airflow, the trajectory is 8.4% lower than one particle system, and the rotation decreases the midair colliding behaviors. A parametric scheme for drag coefficient of sand particle is summarized to modified the macroscopical Eulerian-Lagrangian wind-sand simulation, in which the saltation transport rate varies for different shapes of sand particles. This work indicts that an accurate prediction of shape and rotation effects is required to describe the sand movement and saltation transport.

Optimization designs of artificial facilities in deserts based on computational simulation

“…In the simulations, the longitudinal direction was the same as the streamwise direction, and the horizontal direction was the transverse direction. To evaluate the performance of each type of array on fixing and blocking sand particles, we defined the average of velocities in the plane 0.02 m above the ground as mean velocity of sand particles (Dun et al, 2018), and the longest movement distance of sand particles in the arrays as invasion distance. All the simulated cases are listed in Table 1, and the parameters were sizes of elements, separation distance among the brick, solar panel, building arrays, and panel laying angle.…”

“…The number of theoretical and experimental studies on novel tiled barriers for sand encroachment protection has notably increased, e.g., low-height sand fences (Hatanaka and Hotta, 1997;Bitog et al, 2009;Pye and Tsoar, 2009;Wang et al, 2017), straw checkerboard barriers (Wang and Zheng, 2002;Huang et al, 2013;Bo et al, 2015;Xu et al, 2018;Wang et al, 2020), clay barriers , plastic checkerboard barriers (Liu et al, 2011;Tian et al, 2015), and brick arrays (Zhao et al, 2012). A tiled barrier is usually low in height because 90% of sand grains encountering aerodynamic entrainment are located within 10-50 cm above the ground (Raupach and Lu, 2004;Mohamed and Khalaf, 2005;Jiang et al, 2017;Dun et al, 2018). The straw checkerboard barrier is a typical tiled barrier that is widely used to prevent sand disasters along the railway in China.…”

Effects of Covering Layer of Sand Particles on Particle‐Bed Collision and Aeolian Sand Transport

“…The grids in the bottom layer were encrypted,$${\increment}z=\left({c}^{{n}_{a}-1}{z}_{\mathrm{max}}\right)(c-1)/\left({c}^{{N}_{a}}-1\right)$$ was the grid height, $$c=1.06$$ was the encryption parameter, $${n}_{a}$$was the serial number of the current grid, $${N}_{a}$$ the total number of grids and $${z}_{\mathrm{max}}$$ the max height in the height $$z$$ direction (increased from the bed side) of the computing domain. The initial condition of wind field was provided by formula as (Dun et al., 2017): $$$u=\frac{{u}_{\ast }}{k}\mathrm{ln}\left(\frac{z}{{z}_{0}}\right)$$$ where $$k=0.4$$ was the Karman constant, $${u}_{\ast }=0.2,\,0.3,\,0.45,\,0.6,\ \mathrm{a}\mathrm{n}\mathrm{d}\,0.7\ \mathrm{m}/\mathrm{s}$$ was the friction velocity, $${z}_{0}=30{\fracslash}d$$ was the roughness. As previous study (Huo et al., 2021), we used uniform particle size …”

“…To study the effect of the layer covering the sand particle on aeolian sand transport, we adopted a numerical simulation method. The basic governing equations are explained below (Dun et al., 2017; Huo et al., 2021).…”

“…) was the grid height, 𝐴𝐴 𝐴𝐴 = 1.06 was the encryption parameter, 𝐴𝐴 𝐴𝐴𝑎𝑎 was the serial number of the current grid, 𝐴𝐴 𝐴𝐴𝑎𝑎 the total number of grids and 𝐴𝐴 𝐴𝐴max the max height in the height 𝐴𝐴 𝐴𝐴 direction (increased from the bed side) of the computing domain. The initial condition of wind field was provided by formula as (Dun et al, 2017):…”