Dynamic evolutions of traffic wind influenced by ambient wind for urban road tunnel with shafts

Weihao, Huang; Yan, Tong; Gangyu, Lv; Baolian, Dai; Tao, Peng · 2022 · DOAJ

DOI: 10.1051/e3sconf/202235602014

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Summary

This study investigates the dynamic evolution of traffic wind and its interaction with ambient wind in urban road tunnels equipped with shafts, specifically focusing on naturally ventilated tunnels in China. The research is motivated by the increasing prevalence of such tunnels in cities like Hangzhou, where traffic congestion and the resulting "piston effect" from moving vehicles significantly influence airflow and pollutant dispersion. The authors aim to quantify how ambient wind conditions affect the airflow field, backflow occurrence, and the ventilation efficiency of tunnel shafts. The methodology combines field measurements and numerical simulations. Field data were collected from the Sifan Road Tunnel in Hangzhou over eight months, recording ambient wind speed, direction, and internal air velocity at various points. Based on this data, a three-dimensional physical model of a 200-meter-long tunnel with three lanes and nine vehicles was established. The simulation utilized Fluent 19.2 software, employing the standard k-ε turbulence model and the dynamic mesh technique to simulate vehicle movement. The study analyzed 28 distinct cases varying ambient wind speed ($V_a$) and direction relative to the traffic flow. Key metrics included the height of backflow zones, shaft ventilation efficiency (defined as the ratio of shaft airflow to total tunnel air exchange), and the Richardson number ($Ri$), which represents the ratio of vertical inertial forces to horizontal inertial forces. The results indicate that ambient wind has a limited influence on the overall airflow field and ventilation efficiency within the tunnel but significantly impacts backflow height. When ambient wind aligns with traffic direction, increasing wind speed weakens the backflow effect; conversely, opposing ambient wind enhances backflow. Regarding shaft ventilation, efficiency decreases when ambient wind blows in the same direction as traffic (reaching a minimum of 10%) and increases when blowing in the opposite direction (reaching a maximum of 30%). Furthermore, the Richardson number analysis reveals that when ambient wind aligns with traffic, $Ri$ decreases as wind speed increases, while opposing wind causes $Ri$ to increase, indicating a shift in the dominant force driving fluid motion. The significance of this work lies in providing a clearer understanding of the complex interactions between traffic-induced piston wind and ambient wind in naturally ventilated tunnels. The findings suggest that ambient wind direction is a critical factor in designing ventilation systems for such tunnels, as it directly affects backflow risks and shaft performance. The study validates the use of dynamic mesh simulations with the k-ε model for this type of analysis and offers practical insights for optimizing ventilation strategies in urban tunnel infrastructure.

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• traffic density