The objective of this study is to investigate the air ventilation impacts of the so called "wall effect" caused by the alignment of high-rise buildings in complex building clusters. The research method employs the numerical algorithm of computational fluid dynamics (CFD) to simulate the steady-state wind field in a typical Hong Kong urban setting and investigate pollutant dispersion inside the street canyon utilizing a pollutant transport model. The validation study on our model settings was accomplished by comparing the simulation wind field around a single building block to wind tunnel data. The results revealed that our model simulation is fairly close to the wind tunnel measurements. In this paper, a typical dense building distribution in Hong Kong with 2 incident wind directions (0 o and 22.5 o ) is studied. Two performance indicators are used to quantify the air ventilation impacts, namely the velocity ratio ( w VR ) and the retention time ( r T ) of the dispersion of pollutants at the street level. We found that the velocity ratio at 2m above ground was reduced 40% and retention time of pollutants increased 80% inside the street canyon when high-rise buildings with 4 times height of the street canyon are aligned as a "wall" at the upstream. While this reduction of air ventilation was anticipated, the magnitude is significant and this result clearly has important implications for building and urban planning.

No abstract

[1] This study investigates the wind energy potential in Hong Kong, a region with a complex terrain, by coupling the prognostic MM5 mesoscale model with the CALMET diagnostic model to produce high-resolution wind fields. Hourly wind fields were simulated for the entire year of 2004. The MM5 simulations were performed on a nested grid from 40.5 km down to 1.5 km horizontal resolution. The CALMET meteorological model was used in a domain that includes the entire Hong Kong region with a high horizontal resolution of 100 m. The MM5 model wind field (1.5 km horizontal resolution) output was input into the CALMET diagnostic meteorological model every hour along with an objective analysis procedure using all available observations. Verification was achieved through two steps. In the first step, the data from three meteorological surface stations that were not assimilated into the CALMET model were compared horizontally with the simulated wind fields. In the second step, the simulated wind fields were compared vertically with the vertical wind profile collected from two upper air sounding stations. The results of this study identified the locations of the highest wind energy potential in HK down to 100 m resolution.