## 4 Results and Discussion  
### Analysis of Gas Flow Distribution at Different Wind Speeds  
The process of dust movement after blasting occurs within the continuous gas phase and is influenced by the distribution of wind velocities within the spatial and temporal dimensions of the tunnel. To study the dust dispersion process within the tunnel, we need to investigate the flow field within the tunnel using wind velocity parameters--\(V\) = 9 m/s, 12 m/s, 15 m/s, and 18 m/s--with the height of the ventilation outlet at 2.3 m and the distance from the outlet to the tunnel wall \(L\) = 8 m, which are actual data from the Mong Duong coal mine tunneling area. The results of the wind velocity distribution within the tunnel are as follows. Wind exits the ventilation duct with the specified velocities as mentioned above. The arrangement of ventilation ducts on the tunnel wall, based on the actual conditions of the coal mine, shows that the wind exits the ventilation ducts at high speed, moves toward the face, changes direction, flows back into the tunnel, and finally exits on the opposite side of the tunnel. Observing the cross-sectional profiles at positions 2 m, 6 m, 10 m, 20 m, 30 m, and 40 m in Figures 2-5, it is evident that the wind velocity distribution on the tunnel face is distinct, creating two zones with high wind velocities: the area where wind exits the ventilation outlet and the area opposite, adjacent to the tunnel wall. The remaining central area exhibits lower wind velocities. \begin{table}
\begin{tabular}{c c c c} \hline
**Parameter Name** & **Parameter Setting** & **Parameter Name** & **Parameter Setting** \\ \hline Solver & Pressure-based solver & Min. particle diameter & \(1\times 10^{-6}\) (m) \\ \hline Viscous model & \(k\)—epsilon model & Max. particle diameter & 0.0001 (m) \\ \hline Inlet boundary type & Velocity inlet & Median diameter & \(1.5\times 10^{-5}\) (m) \\ \hline Inlet velocity & 9 m/s; 12 m/s; 15 m/s; 18 m/s & Distribution index & 3.5 \\ \hline Outlet boundary type & Pressure outlet & Mass flow rate & 0.0012 kg/s \\ \hline Material & Coal—hw & Height of the air duct & 1.1 m, 1.4 m, 1.7 m, 2.3 m, 2.7 m, 3.0 m \\ \hline Diameter distribution & Rosin–Rammler & Injection type & Surface \\ \hline Number of timesteps for transient simulation & 600 s & Material & Coal—HV \\ \hline Drag law & Spherical & Physical models; Saffman & \\  & & Lift force & DEM Collision \\ \hline  & & & Interaction: interaction with continuous phase; particle \\ \multirow{2}{*}{DPM-boundary type} & \multirow{2}{*}{Reflect} & \multirow{2}{*}{Discrete Phase model} & Interaction: interaction with continuous phase; particle \\  & & & treatment: unsteady particle \\ \multirow{2}{*}{DPM-boundary type} & \multirow{2}{*}{Reflect} & \multirow{2}{*}{Discrete Phase model} & \multirow{2}{*}{tracking; Stochastic tracking: discrete random walk model} \\ \hline \end{tabular}
\end{table} 
Table 1: Fluent model configuration parameters. Subsequently, the wind continues to move, and the wind velocity in the section near the ventilation outlet gradually decreases to a stable level. Meanwhile, the higher wind velocity occupies the other side of the tunnel, covering approximately half of the tunnel's cross-sectional area, as shown in Figures 2-6. Figure 2, based on longitudinal cross-sections along the tunnel, demonstrates that within approximately 20 m from the tunnel's back, an uneven wind distribution exists. Higher wind velocities are concentrated on the right side of the tunnel, while lower velocities are found on the left side. The central portion experiences the lowest wind velocity within this distance. This indicates that the wind flow becomes more stable, reducing small variations. This is attributed to the influence of the wind flow rebounding after colliding with the tunnel wall and the wind exiting the ventilation outlet, which generates a vortex region, resulting in lower wind velocities within this area. Figure 3: Velocity distribution on longitudinal cross-section along the heading face with \(V=12\) m/s.