Laboratory measurement of electrification of wind‐blown sands and simulation of its effect on sand saltation movement

Abstract

[1] This article presents a measurement of electrification generated by wind-blown sands in a field wind tunnel and a numerical methodology to simulate the effect of electrification on the sand saltation movement after the mutual couple interaction between the sand movement and the wind flow is taken into account. The measured data of electric charge on the ''uniform'' sands in the wind-tunnel tests show that the sign of electric charge, either negative or positive, is mainly dependent on the diameter size of sand particles, i.e., negative charge is gained when the diameter is smaller than 250 mm and positive charge is obtained if the diameter is larger than 500 mm, and that for both ''uniform'' and mixed sands, the average charge-to-mass ratio decreases with increasing the wind velocity, and increases with height from sand bed. Meanwhile, the measurement of electric field in wind-sand cloud related to the electric charge displays that the magnitude of electric field increases generally as the wind velocity and the height increase, and the direction of the field is always upwardly vertical to the Earth's surface, which is opposite to that of the fair-weather field. In order to exhibit the effect of electrification on sand saltation movement, a theoretical model by considering the mutual coupling interaction between wind flow and sand movement is proposed after the electric force exerted on the moving sands is considered. Through solving the nonlinear coupling dynamic equations by a proposed program, the effect of electrification on sand saltation motion, e.g., trajectory, is discussed quantitatively. After that, its effect on wind-sand transport flux, sand ejecta flux, and wind profile is also displayed. The results show that the prediction for the Bagnold's kink is good agreement with the measurement in literature.

Applications of Electrified Dust and Dust Devil Electrodynamics to Martian Atmospheric Electricity

“…In experimental studies the electric fields generated by terrestrial dust devils support the idea that suspended dust becomes electrified negatively with respect to the sand/sand-bed (Schmidt et al 1998;Zheng et al 2003;). This size dependence has been best demonstrated in laboratory experiments involving sand cascading Kok and Lacks 2009;Lacks and Levandovsky 2007, Forward et al 2009a, 2009bBilici et al 2014).…”

“…Considering the potential electrical force exerted on micron size dust particles by electric fields predicted inside dust devils or dust storms, electrification may potentially contribute to the global transport of dust at a level comparable as the drag force due to the wind (Berthelier et al 2000). Studies have explored the more specific impacts of electrification on the lifting processes of dust from the surface of Mars, unveiling the unexpected role of electrification in the trajectories of saltating particles, an effect first suggested by Schmidt et al (1998) and Zheng et al (2003). A major effect concerns the limitation imposed by electric forces on the height of the saltation layer.…”

“…There is less success in establishing expected/limiting values. In aeolian sand transport studies values have been quoted of order 60 µC kg −1 , (Schmidt et al 1998;Zheng et al 2003Zheng et al , 2004Bo et al 2014). In gas-solid pipe flows continuous sand transport is performed while measuring the current to metal pipe, here values of order 3 mC kg −1 have been measured (Matsusaka et al 2010).…”

“…In laboratory experiments of sand transport in the absence of dust, it has been seen that sand may electrify either positively or negatively depending on the size distribution within the sand bed (Bo et al 2014;Zheng et al 2003, Kok and Renno 2008a, 2008b. Laboratory experiments have also shown that dust re-suspension in the absence of sand shows little net (size dependent) dust electrification , however the role of dust aggregates (acting like large sand-sized particles) could possibly complicate this behaviour.…”

Review and Assessment of Electromagnetic Wave Propagation in Sand and Dust Storms at Microwave and Millimeter Wave Bands --- Part Ii

“…It is to be noted, however, that the general conclusion by these workers was that except for very dense storms and charged particles, attenuation by dust storms is not serious. Lastly, many measurements and theories [24,30] show that sand particles in SDS carry charges on them, and they have an effect on the wind-sand movement. Thus, in addition to the factors already considered in the MW attenuation, Zhou et al [31] incorporated the factor of charges on dust particles.…”