Study on the reasonable tilt angle of ventilation shafts in Xidianwan Tunnel, China

Abstract

The “asthma effect” of shaft natural ventilation is common, which makes the actual air exchange volume impossible to be quantified and the pollutant concentration along the tunnel unable to be analyzed. In order to improve the ventilation effect of the ventilation shaft and realize the steady air flow in the air well, the reasonable tilt angle of the ventilation shaft is studied. Firstly, the numerical simulation software FLUENT is used to establish a tunnel model of a certain traffic volume based on dynamic grid technology, and to analyze the relationship between the shaft tilt angle and the air flow state, including intake and exhaust air volume, and air flow direction. Secondly, model experiments are carried out to verify the numerical simulation results, in which jet fan thrust pressure is substituted for traffic piston pressure. The result shows that the natural ventilation state with the proposed direction can be realized on condition that the shaft tilt angle is around 15 degrees. That means to discharge polluted air from one group of ventilation shafts and suck in fresh air from the other group of ventilation shafts. At the same time, by dividing the tunnel rationally, the calculation formula of pollutant concentration of the cross section along the tunnel under the condition of different diverging amounts caused by the change of tilt angle of the ventilation shafts is derived, which provides guidance and reference for determining whether the air quality in the tunnel meets the requirements of relevant specifications.