Effect Of Shaft Position On Ventilation Flow Field In High-altitude Single-track Single-hole Super Long Railway Tunnel

Due to the high natural wind speed in high altitude areas and the significant thermal heading effect of high-altitude tunnels with auxiliary tunnels,the effects of natural wind in tunnels should be fully taken into consideration when designing and operating ventilation in high altitude tunnels.In long deep tunnels with vertical shafts,the height difference between the shaft and the two openings is significant,which makes the air temperature difference and pressure difference in the tunnel form a strong chimney effect,thus affecting the effect of natural ventilation.Because of the characteristics of the chimney effect of the shaft,the excellent effect of smoke exhaust on the tunnel during the fire,the effect of rapid exhaust smoke in the tunnel is more obvious.Therefore,the effective use of construction auxiliary tunnels during operation not only saves costs,but also improves the local ventilation environment of the tunnel.Based on the natural ventilation in a 3000 m tunnel with no vertical shaft,theoretical calculations and numerical simulations are performed for the natural ventilation flow field of the tunnel when the temperature difference between the hole inside and outside is 5°C and 10°C,respectively,and gets the natural wind speed inside the tunnel under two conditions in this paper.Comprehensive analysis of theoretical calculations and numerical simulations shows that the theoretical wind speed results in the tunnel can be controlled within 7%,which verifies the correctness and feasibility of numerical simulation.Based on the FLUENT software,the distribution of natural wind flow when the shaft located at different positions in the tunnel is simulated and analyzed.The following conclusions are drawn:(1)With the increase of the distance from the tunnel entrance in the vertical direction of the tunnel,the natural wind speed in the tunnel decreases,and the tunnel ventilation time increases according to the e-index.The lateral small distance movement of the shaft has little effect on the natural wind speed in the tunnel.(2)The velocity at the entrance and exit of the tunnel and the longitudinal position of the shaft are decayed by an e-index.The velocity of the tunnel shaft exit is less affected by the vertical position of the shaft,and the maximum rate of velocity fluctuation is not greater than 1.6%.Based on the FLUENT dynamic grid technology,the distribution law of the piston of a tunnel in a single vertical shaft tunnel is simulated and analyzed.The conclusion is drawn that the flow field in front of the train is fan-shaped and forwards,and several tail vortex zones are formed at the rear of the train;The flow in the gap space is roughly as follows: near-train wall airflow velocity is relatively large,near-tunnel wall airflow velocity is small,longitudinal annular air flow velocity gradually decreases from the front to the rear;the velocity field of the fluid in the shaft is affected by the piston wind The fan-shaped distribution has a significant effect on the posterior segment of the annulus space flow field,and the shunting action reduces the supercharging of the shear force.