Analysis of Individual Ventilation Effects of Down Steps in Highway Gas Tunnel Construction with the Up-and-Down-Steps Method

To study the influences on the down-step ventilation of highway gas tunnel in the progress of the up-and-down-steps method construction, three-dimensional models of the tunnel were built and simulated numerically with the software Fluent, which is based on fluid dynamics theory. A comparative analysis of flow velocity under the condition of five different kinds of distance between the air duct exit and down-step face was made. The impact of arrangement form of air duct was further explored. The simulation results show that the progress of individual ventilation would disturb the air particles in the evacuated up step; under the same entry speed conditions, the closer the duct exit is to the down-step face, the bigger the velocity gradient of jet would be there; the arrangement form of duct would cause less effect on the velocity of air particles that are far from the step.