Experimental measurement of wind-sand flux and sand transport for naturally mixed sands

Abstract

This article presents an experimental test and a program to empirically fit experimental data for the horizontal flux of wind-blown sand passing through a unit area along a vertical direction per unit time. The experimental data for the sand flow flux as a function of the height for naturally mixed sands, which were chosen from a sand dune at the southeastern edge of the Tengger desert, were measured with a sand collector in a field wind tunnel. On the basis of the experimental data and a least squares method, a fitting program is proposed here and, further, an explicit form of an empirical formula varying with height and axial wind velocity or friction velocity for the flux structure of the sands is gained. After that, we obtain an explicit form of the empirical equation for the measurement of streamwise sand transport per unit width and unit time by integrating the empirical formula for sand flux along the height direction and considering the contribution of sand creep. Finally, we evaluate the effectiveness of the predictions of some equations, especially the well-known Bagnold equation and Kawamura equation, for predicting streamwise wind-sand transport using the empirical equation obtained for mixed sands. The results show that the predictions from Bagnold's equation in the region of friction velocity u(*)>0.47 m/s and Kawamura's equation in the region u(*t)<or=u(*)<0.35 m/s are effective. Meanwhile, the measurement results given from the empirical equation smoothly transit from Kawamura's prediction to Bagnold's prediction as the friction velocity increases in the range 0.35 m/s<u(*)<0.47 m/s.

A probability density function of liftoff velocities in mixed-size wind sand flux

“…These PDFs of liftoff velocities are valid under the log-normal diameter distribution given in ref. [13]. …”

“…In order to emulate natural sand particle-bed collision, natural sand particles are sampled from sand dune in southern area of the Tengger desert in China, and their particle diameters obey a lognormal distribution (see Figure 2) [13] . In the simulation, particle diameters are divided into 10 representative sets: 0.09 mm, 0.12 mm, 0.14 mm, 0.16 mm, 0.18 mm, 0.19 mm, 0.2 mm, 0.21 mm, 0.28 mm and 0.45 mm.…”

Field driven charging dynamics of a fluidized granular bed

“…This is the boundary condition used in Ref. [25], which permits the injection of charge into the bed to mimic field and laboratory observations [27,[37][38][39]. Second, to prevent spurious repetition of charging, we only apply induction and neutralization operations (Eqs.…”

Effects of the mid-air collision on sand saltation

“…Saltation is the primary means by which sand-sized particles travel in most realistic winds [1] , so it is the most important subject in blown sand research. Based on experiments, some scholars obtained empirical formulae of sand mass-flux in the near surface layer [2] . Meanwhile, some scholars numerically simulated the transport sand mass, and predicted the effects of coupled interaction of wind velocity, temperature field, electric field and sand movement and the factors of the electrification of sand particles, mixed radius and pulsating effect on the saltation grain number, the mass flux and the time for the entire system to reach a steady state [3][4][5] of wind-blown sand flow through different theoretical models.…”