Analysis of numerical factors affecting large eddy simulation of pollutant diffusion around buildings

Abstract

In recent years, Large Eddy Simulation (LES) has been often used for predicting the pollutant diffusion around buildings. However, due to the numerical discretization error and the sub-grid scale modeling error, some empirical factors related to LES have not yet formed with completion for the best practice. This study focused on LES simulation of the airflow and pollutant diffusion around building with a synthetic inflow turbulence method and Wall-Adapting Local Eddy-Viscosity (WALE) model, discuss LES empirical factors, such as effects of grid resolution, sub-grid scale (SGS) WALE model with coefficient Cw and the sub-grid scale Schmidt number ScSGS in details. The results indicate that the numerical wind tunnel created by LES can better reproduce the characteristics of the airflow and concentration field around buildings while keeping predicted physical fields are in line with the evaluation index. In addition, the results also indicate that the solution with the finest grid resolution may not have the best agreement with the experimental data, the flow field is more sensitive to the change of SGS model coefficient Cw when the grid resolution is lower, which shows a trend that the larger coefficient Cw has better simulation in the windward sides of the building, while the value of the coefficient Cw shows an opposite trend in the recycling area at the rear of the building.