Numerical simulations of asymmetric wind-driven rain on airflow and smoke dynamics in tunnel fires

Abstract

Tunnel fire behavior is significantly influenced by external environmental factors, yet the role of wind-driven rain (WDR) remains underexplored. This study numerically investigates the effects of asymmetric WDR on the flow field and smoke movement in tunnel fires. A three-dimensional numerical model is established to account for WDR-airflow-smoke interactions. Simulations are performed with varying crosswind velocities and rainfall intensities. Results show that rainfall induces a uniform longitudinal flow driven by a sustained pressure gradient, whereas the introduction of crosswind generates boundary-layer separation and vortex structures near the windward tunnel portal. The velocity of the induced airflow may decrease under the combined influence of crosswind and rainfall compared to that under rainfall alone. Once a fire occurs in tunnels under WDR conditions, the induced airflow significantly alters smoke dynamics. The variation in back-layering length under WDR is closely related to the induced airflow velocity. Fires occurring near the WDR-affected portal are particularly hazardous, as vortices obstruct smoke overflow, leading to smoke accumulation and even tunnel filling. These findings provide new insights into the interaction between WDR and smoke flows in tunnel fires, offering guidance for safety design and ventilation strategies under extreme weather conditions.