Laboratory measurement of saltating sand particles' angular velocities and simulation of its effect on saltation trajectory

Abstract

[1] This paper reports a laboratory observation of spin attitudes and angular velocities of saltating sand particles in wind-blown sand flux by using the high-speed and dynamic cinecamera and presents a numerical simulation to show the effect of spin on the saltating trajectories of sand particles. Experiment results show that a saltating sand particle has two basic spin attitudes, rolling spin (W x , which is perpendicularity to wind direction and parallel with sand surface) and left/right spin. The percentages of the former and the latter attitude are 5% and 95%, respectively. The left/right spin angular velocities range from 0 revolutions per second (''rev/s'' henceforth) to 800 rev/s and obey a single-peaked distribution, the peak value of which lies in (150 rev/s, 250 rev/s). The rolling spin angular velocity of a saltation sand particle is variational along its entire saltating trajectory. The left/right spin vector is composed of two spin components, W y (called lateral spin component, rotating around the wind direction) and W z (called up spin component, rotating around the axis perpendicular to the sand bed). The theoretical simulation indicates that lateral and up spin components not only have effects on the trajectories' scales (i.e., heights and lengths) but also have effects on the trajectories' dimensions, especially when they are higher than 2000 rev/s and 200 rev/s, respectively. While the rolling spin angular velocities only change the trajectories' heights and lengths, especially for the rolling angular velocity higher than 300 rev/s.

Mechanics of Wind-blown Sand Movements

“…Their results show that the resultant of lateral and rolling angular velocities, namely the left/right angular velocities are typically in the region of 200-300 rev·s -1 and the maximum value can reach up to about 1000 rev·s -1 , which agree well with the experimental results (Xie et al 2007). Through solving the equations of a 3-D model, deduced not only horizontal and vertical components of lift-off velocities, with the angular velocity rotating around the x axis (named rolling angular velocity), but also the lateral velocity, the lateral angular velocity rotating around the y axis and the upward angular velocity rotating around the z axis.…”

“…The experiment was conducted in a blow-type, noncirculating wind tunnel. Two basic spin patterns captured by dynamic cinecamera (a) in-plane spin, the rotation axial prallel with the linear velocity, and (b) out-plane spin, the rotation axial perpendicular to the linear velocity (from Xie et al 2007) taken by the dynamic cinecamera, in each of which a segment of trajectory of a saltating particle is captured. The sand particles were laid on the bed with a thickness of 5 cm in the tunnel.…”

“…Probability distribution of left angular velocities, analyzed by the equal distance histogram method on the basis of 1335 clear segments of saltation trajectories (fromXie et al 2007) …”

Vertical distribution of wind–sand interaction forces in aeolian sand transport

“…According to the experiments of Ling and Wu (1980), Xie et al (2007) further analyzed the spin attitudes and angular velocities of the saltating sand particles. The results show that a saltating sand particle has two basic spin attitudes, i.e., rolling spin and left/right spin.…”

Influence of particle rotation on the oblique penetration in granular media

“…Moreover, most investigations have not considered the influence of particle rotation on dynamical behaviors and the evolution of impacting craters. Whether a sand particle impacts a granular bed [34], or a meteorite impacts a planet [35], the projectile usually has a certain initial angular velocity.…”