# Study on Airflow Field Distribution and Dust Distribution Characteristics at Blast Piles
## 2 Methods
### Open-Pit Coal Mine Model  
As revealed by the above research, the dust at the blasting pile enters the atmosphere due to both natural airflow and the disturbance of shovel loading. Therefore, in this study, we will first analyze the distribution characteristics of the airflow field at the blasting pile. Based on the practical situation of the open-pit mine with appropriate simplifications, this article has established a model of an open-pit coal mine as shown in Figure 4. The simplification of the model mainly comes from two aspects, one is to omit the bench slope  
Figure 3: The dust escapes during the shoveling process. Figure 2: Blast pile. and the other to treat the blast pile and other deposits as a whole. This model comprises an upper air layer and a lower open-pit mine pit. The model measures 1000 m in length, 500 m in width, and 205 m in depth. Inside the mine pit, there are five layers of benches, with each bench having a platform width of approximately 50 m and a bench height of approximately 15 m. The height of the bench closest to the coal seam roof is approximately 45 m, and the length of the coal seam roof is about 85 m. According to the characteristics of the mining and dumping sides within the open-pit mine, the slope angles of the dumping side from the first to the fifth layer are 60\({}^{\circ}\), 70\({}^{\circ}\), 80\({}^{\circ}\), 80\({}^{\circ}\), and 85\({}^{\circ}\), respectively; while the slope angles of the mining side from the first to the fifth layer are 45\({}^{\circ}\), 35\({}^{\circ}\), 25\({}^{\circ}\), 25\({}^{\circ}\), and 20\({}^{\circ}\), respectively. Mining waste is concentrated and dumped in the spoil dump. Consequently, the left side with a steeper slope angle represents the dumping side, while the right side with a shallower slope angle represents the mining side. Given the varying airflow characteristics at different benches, the model is divided into five layers, with specific dimensions detailed in Table 1. Before the numerical simulation study, we selected several different mesh sizes, carried out CFD simulation on the model under each size, and analyzed the convergence and stability of the simulation results (such as flow field distribution, pressure distribution, velocity distribution, etc.). By comparing the simulation results of different mesh sizes, we determine a mesh size that can guarantee the simulation accuracy and effectively control the calculation cost. Within this context, the left inlet of the air layer is set as a velocity-inlet boundary, while the outlets of other surfaces of the air layer are outflow boundaries. The hydraulic diameter is 166.7 m, and the turbulence intensity is 5%. The steady-state solver and Standard k-\(\varepsilon\) \begin{table}
\begin{tabular}{c c} \hline \hline
**Geometric Model** & **Dimension** \\ \hline Air layer & 1000 m (length) \(\times\) 500 m (width) \(\times\) 100 m (height) \\ Open-pit mine floor & 85 m (length) \(\times\) 100 m (width) \(\times\) 45 m (height) \\ Platform & 50 m (width) \(\times\) 15 m (height) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameter settings of the geometric model. Figure 4: Geometric and computational mesh model of open-pit mine: (**a**) Overall grid; (**b**) Grid profile. model are selected [29], and the Simple algorithm is utilized to solve the airflow field in the open-pit coal mine by Ansys Fluent, aiming to find the continuous-phase airflow field. Ansys Fluent software 2023 R1 includes rich and advanced turbulence models that enable users to accurately simulate free flow, laminar flow, and turbulence. In order to verify the reliability of the numerical simulation model, the data calculated in the numerical simulation are compared with the data measured in Hedaigou open-pit coal mine. On site, the dumping side and the mining side are measured at a depth of about 100 m, 85 m, and 70 m from the bottom of the pit. The point selection function is adopted in the numerical simulation model to select the point at the corresponding depth from the bottom of the pit.