# Dust Dispersion Characteristics of Open Stockpiles and the Scale of Dust Suppression Shed
## 1 Introduction  
With the increasing focus on the natural environment and human health, the control of fugitive dust emissions is receiving more and more attention [1]. Dust is released from a variety of sources, such as the unloading of bulk materials, mechanical transport of bulk materials, and the wind erosion of open storage piles. In the storage of bulk solids, dust emission often occurs because of air movement around or into and out of granular material. There are few studies on the dust dispersion from open piles. Wind field analysis and the evaluation of dust emission rates are important aspects to study the dust dispersion from stockpiles. Prediction of dust emissions by numerical CFD simulations is conducted to obtain velocity distributions on individual pile surfaces [2]. Turbulence and complex topography have a significant effect on the dispersion of dust as well as the distribution of deposition [3]. Total fugitive dust emissions at high wind speeds (15 m/s, 25 m/s respectively) were quantified [4]. Moreover, the factors influencing the dust release rate from storage piles have attracted attention in a few literature works. [PERSON] et al. proposed that the diffusivity of dust was positively correlated with the pressure drop. The shape of stockpile is also associated with dust emissions, e.g., conical stockpile [5] versus flat-topped stockpile [6]. Meanwhile, the sparseness of stockpile arrangement has a significant effect on the dust emissions [7]. In a close arrangement, the downwind direction of the sand pile creates a shadow that reduces dust release from the pile located downwind [4; 7]. The shape of the sand pile also had a significant effect on dust dispersion, and he found that semi-circular piles produced less dust emissions than flat-topped and tapered piles for the same stockpile configuration [8]. Intermediate pile height configurations can also reduce dust emissions from stockpiles [9]. In terms of particle size, the impact of stockpiles on ambient PM10 concentrations on a large scale has also been predicted [1]. However, the effect of wind speed has not been studied thoroughly enough on dust dispersion from sand piles up to now. In more detail, dust dispersion has been studied extensively, encompassing all aspects. First, in studying the mechanisms of diffusion and the factors that influence it, many scholars have investigated the effects of particle roughness [10], changes in airflow [11; 12], spatial layout [13], and pore space in particle accumulation [14] on the dust diffusion. Second, some researchers have investigated dust suppression measures [15], such as the use of surfactants [16] and ventilation conditions [17] to suppress dust. Third, the research methods for dust dispersion are mainly experiments and numerical simulations to verify each other. Numerical calculation methods include discrete phase model (DPM) [5], discrete element method (DEM) [14; 18; 19], etc. The methods above have their own use scenarios, with the DPM method being more widely applicable. DPM is advanced for modeling gas-solid two-phase flows of dilute bulk particles. The DPM method has been used in many studies on gas-solid two-phase flows [20; 21; 22]. DPM cannot simulate gas-solid two-phase flows with high volume fractions due to the fact that the DPM model ignores particle-particle forces. However, it has also been suggested that the loss of energy can be approximated to account for collisions between particles [19]. The subject of this study is a stockpile with a low volume fraction of gravel for dust dispersion. Therefore, the DPM method is applicable to this study. The gravel is reduced to a spherical particle model, which introduces a small degree of error. It is the gravel with a low water content that causes significant dust lifting. For this reason, we do not consider wet particles in simulations. Research has been carried out in order to ensure that the fugitive dispersion of open storage piles does not affect the urban environment as well as human health.