Experimental Study on the Effect of Particle Shape on Rotational and Translational Speeds in Aeolian Sand Transport

Abstract

The particle shape is an important factor affecting the rotational and translational speeds of sand particles, but the relationship between particle shape and speed is still unclear. The high-resolution and high-speed camera technology (31.6 μm/pixel and 10 000 frames/s) is applied in a wind tunnel to study the characteristics of rotational and translational motion of particles with different shapes. The results show that with increasing circularity, the mean rotational speed decreases for smaller particles less than 0.4 mm in diameter and increases for larger particles more than 0.4 mm in diameter, whereas the mean translational speed usually increases for all particles, clockwise and counterclockwise rotational particles. At the same circularity, the mean rotational speed and proportion of clockwise rotation are higher than those of counterclockwise rotation, whereas the mean translational speed of clockwise rotation is usually less than that of counterclockwise rotation. With increasing circularity, the mean rotational speed of particles increases below 10 mm height, but the mean translational speed of particles decreases. The probability density distribution of rotational speed of particles with different circularities is described as a Lorentz distribution, whereas the probability density distribution of translational speed is represented as a lognormal distribution. The mean rotational speed of particles has generally a positive correlation with the mean translational speed. Therefore, particle shape (or circularity) should be considered as an important factor affecting particle motion in the study of particle trajectories and speeds during saltation.