Transfer and escape characteristics of outdoor pollutants into an indoor space sheltered by urban-like block arrays using large-eddy simulations

Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Japan

^* Corresponding author: fernandez.ken.bryan.487@s.kyushu-u.ac.jp

Abstract

We conducted isothermal large-eddy simulations to generate the velocity and concentration distributions to investigate the air pollution transport from outside to inside of a space surrounded by urban-like block arrays. Contrary to previous study, we assumed that the pollution in the form of scalars are generated outdoors and not indoors which we placed at: 1) middle of window, 2) near window wall, 3) middle of street canyon at ground level, and 4) middle of street canyon at window level. Results showed that regardless of scalar source location, the scalars accumulated inside the indoor space which can be explained by the downdraft effect that are typically found in urban environments. The downdraft effect produced vortices outside and inside the indoor space. For scalars near window, indoor vortex drove the concentration to indoors. On the other hand, outdoor vortex transported the scalars located at street canyon to reach the window where they were eventually transported to indoors also due to indoor vortex. The average normalized indoor concentrations found in this study are 1.25 – 1.50, 1.00 – 1.75, 0.25 – 0.50, and 0.0 – 0.25 for scalars C₁, C₂, C₃, and C₄, respectively. Our study suggests that for natural ventilation studies of urban environments where air pollution is significant, outdoor effects should also be carefully considered.