Calculation method for air resistance coefficient of vehicles in tunnel with different traffic conditions

Abstract

Extra-long tunnels are developing rapidly as an option for transportation systems. However, owing to their complex configurations, harmful pollutants can easily accumulate, leading to increased reliance on mechanical ventilation systems. Traffic wind can also be used to supplement ventilation. Nevertheless, current tunnel ventilation guidelines cannot accurately reflect the traffic wind. Moreover, wind tunnel tests and numerical methods are time consuming, and do not generally incorporate different traffic conditions. In this study, traffic conditions in a tunnel are quantified into five traffic condition parameters: distribution of lanes, vehicle distance, blockage ratio, vehicle speed, and proportion of large-scale vehicles. Using a computational fluid dynamics (CFD) method, the influences of the five parameters on the air resistance coefficients of vehicles in the tunnel are investigated. The results show that the distribution of lanes, blockage ratio, vehicle distance, and proportion of large-scale vehicles have significant influences on the air resistance coefficients of the vehicles; however, the impact of the vehicle speed is small. Based on the results, a general calculation method for the air resistance coefficient of vehicles in a tunnel is developed, considering the blockage ratio, vehicle distance, and proportion of large-scale vehicles in actual traffic conditions. The method shows acceptable accuracy (with relative errors of less than 10%), and is convenient for use in the design and operation of tunnel ventilation.