Tall-building effects on pedestrian-level flow and pollutant dispersion: Large-eddy simulations

Abstract

The urban environmental impact of tall buildings has increasingly become an important topic of investigation, with the rapid pace of tall-building constructions around the world. In this study, the effects of a tall building on pedestrian-level flow and pollutant dispersion are investigated using the parallelized large-eddy simulation model (PALM). Numerical simulations are conducted by changing the tall-building height in the configuration of a tall building surrounded by low-rise cubical buildings. As the tall-building height increases, the time- and area-averaged pedestrian-level wind speed and pollutant concentration increases and decreases, respectively. Both the rates of changes in the average wind speed and pollutant concentration decrease with increasing tall-building height. The trend of the average wind speed is attributable to an increasing tendency of oncoming flows to pass by the sides of the tall building rather than going down as the tall-building height increases. The trend of the average pollutant concentration is associated with that of the average wind speed. Instantaneous flow and pollutant dispersion are also analyzed. In the upstream region of the tall building, bulks of polluted air are repeatedly transported from further upstream regions and enter the canyon right in front of the tall building, temporarily increasing the pedestrian-level pollutant concentration near the windward wall of the tall building. In the downstream region of the tall building, at the pedestrian level, two counter-rotating vortices appear in the canyon just behind the tall building. Each of these vortices repeatedly develops at one of the two leeward corners of the tall building, moves downstream while changing its size, and disappears after reaching the windward wall of the neighboring low-rise building. These coherent vortices considerably affect the spatiotemporal variation of pedestrian-level pollutant concentration in the canyon just behind the tall building.