Dispersion of ultrafine particles in the wake of car models: A wind tunnel study

摘要

Worldwide around 7 million annual deaths are due to air pollution. Among all pollutants, Ultrafine Particles (UFP) cause strong adverse effects. In this paper, the dispersion of UFP is studied in the wake of car models characterized by different rear slant angles (phi). Velocities and UFP concentrations are collected in a wind tunnel. The influence of the flow topology on the dispersion of these UFP is discussed. The results indicate that its structure strongly influences their dispersion. Whatever the rear slant angle is, the size of the recirculation region is a key parameter governing the dispersion of these UFP. For phi = 0 degrees, the flow is almost symmetric and concentration levels are higher and homogeneous in the close wake. The recirculation region is the largest one. The dispersion is enhanced in both horizontal and spanwise directions. For phi = 25 degrees, the flow is attached on the rear slant leading to a strong downwash effect. The volume of the recirculation region is the smallest. Longitudinal vortices develop from the edges of car model entrapping particles. Particle Number Concentration field is no more symmetric. For phi = 35 degrees, results are almost similar to those obtained for phi = 0 degrees. Comparisons with previous studies are discussed and possible applications are suggested.