Large-Eddy Simulation of pollutant dispersion around a cubical building: Analysis of the turbulent mass transport mechanism by unsteady concentration and velocity statistics

Pollutant transport due to the turbulent wind flow around buildings is a complex phenomenon which is challenging to reproduce with Computational Fluid Dynamics (CFD). In the present study we use Large-Eddy Simulation (LES) to investigate the turbulent mass transport mechanism in the case of gas dispersion around an isolated cubical building. Close agreement is found between wind-tunnel measurements and the computed average and standard deviation of concentration in the wake of the building. Since the turbulent mass flux is equal to the covariance of velocity and concentration, we perform a detailed statistical analysis of these variables to gain insight into the dispersion process. In particular, the fact that turbulent mass flux in the streamwise direction is directed from the low to high levels of mean concentration (counter-gradient mechanism) is explained. The large vortical structures developing around the building are shown to play an essential role in turbulent mass transport. Highlights: ► Large-Eddy Simulation of pollutant dispersion around a cubical building. ► Computed average and standard deviation of concentration are compared to measurements. ► Contribution of subgrid scales to turbulent mass flux is evaluated. ► Turbulent mass transport is analyzed by velocity and concentration statistics. ► These statistics are linked to the turbulent flow structure around the building. - Large-Eddy Simulation is used to simulate pollutant dispersion around a cubical building and to compute statistics of concentration and velocity fluctuations, which provides physical insight into the turbulent mass transport process.