Deposition and dispersion characteristics of ultrafine particles under different vehicle speeds in road tunnels employing dynamic mesh simulation.

The purpose of this study is to analyze the unsteady turbulence, deposition, and dispersion characteristics of ultrafine particles of different sizes during the passage of vehicles through a road tunnel. We present a realizable k-ε turbulence model based on a combination of Eulerian passive scalar and dynamic mesh models. A 100-m three-dimensional model of a road tunnel containing four vehicles in a row and 10-m long outlets was established using STAR-CCM+ computational fluid dynamics software. Ultrafine particles derived from vehicle exhaust gas were modeled at velocities of 60, 40, and 20 km h. The diameter and number of particles ranged from 26 to 287 nm and 1.7 × 10-1.7 × 10 cm, respectively. The results show that, in the vertical plane (located 0.1 m behind the exhaust pipe), the deposition effect cannot be ignored at low velocity. Furthermore, the particle concentration distribution both in the breathing zone and the entire tunnel is not significantly affected by deposition.