## 2 _Introduction_  
In the mine production system, the movement of mine equipment will produce a lot of induced airflow, such as the middle transport equipment (rail or trackless equipment), mine lifting equipment (skip or cage), mine or ore funnel or drawing. Among them, the piston airflow generated by the operation of the middle transportation equipment and the mine hoisting equipment has the greatest influence on the stability of the mine ventilation system. With the continuous improvement of mine mechanization and mine production capacity, the development of underground lifting equipment tends to be large-scale and efficient [1]. Cage in the wellbore operation, the speed is usually up to 6-12 m/s, and underground ore lifting, material decentralization, personnel and equipment transportation are inseparable from the cage or skip in the shaft lifting [2]. The frequent lifting and lowering of cages and skips in the well will lead to the continuous change of the effective cross-sectional area of the wind in the limited space of the well, which will produce the transient change of the piston airflow and the wellbore pressure, and the piston wind problem becomes prominent. The main intake shaft in the mine is often connected with multiple transportation lanes. The piston effect caused by the wellbore is bound to affect the airflow field and lane pressure in the lane. The transportation lane also undertakes the transportation of underground fresh air flow and leads to the main production area. The piston effect causes the normal air to flow in the lane to be destroyed, and the impact on the stability of the mine ventilation system cannot be ignored. [PERSON] [3] measured typical lanes in suburban coal mines in Henan Province, China. It was found that the piston wind generated by different operating states of the mine car has a great influence on the ventilation resistance of the lane, which will affect the stability of the ventilation system in the difficult period of ventilation. [PERSON] [4] measured the local resistance of the auxiliary shaft of Gequan Mine in Hebei Province, China. It was found that the transient local resistance caused by the piston effect of the lifting container accounts for 47.64% of the ventilation resistance of the whole auxiliary shaft, which seriously hinders the air flow. At present, research on piston wind mainly focuses on subways and tunnels. In 2007, [PERSON] et al. [5] studied the unsteady three-dimensional flow caused by train operation in subway tunnels for the first time through 1:20 train and tunnel model tests and CFX4 and analyzed the changes of pressure and wind speed with time. The piston wind of trains in the tunnel is of great significance to tunnel ventilation and fire rescue. Based on the sliding mesh technique, [PERSON] et al. [6] established a three-dimensional computational model of high-speed trains and tunnels and studied the piston wind effect caused by two trains passing each other in the tunnel. The results show that the piston effect is more obvious when the train is limited by multiple trains in the same space, and the difference in the maximum peak at different positions is 34% larger than that of the single train. Based on a three-dimensional compressible turbulence model, [PERSON] et al. [7] studied the pressure waves generated by two trains passing each other in the tunnel. The simulation results show that the train pressure and resistance coefficient reach the maximum when the two trains intersect in the tunnel. Due to the interaction between the train and the tunnel, the pressure and drag coefficients increase with the increase in train speed and blockage ratio. [PERSON] et al. [8] simulated the movement of trains in subway tunnels and stations on a side subway platform based on a 3D computational model. The results show that when the train just enters the station and brakes, some particles are transported and spread to different platform areas.