The Impact of High-rise Building Form on Climatic Comfort at the Pedestrian Level

Wind is one of the climatic factors which can be affected by the urban development. Wind speed, wind direction, air pollution, rain, radiation and daylight are all examples of physical aspects that constitute the outdoor climate, and that are changed by the presence of the buildings. The change of these quantities depends on the shape, size, and orientation of the building and on the interaction of the building with the surrounding buildings and other obstacles such as trees etc. In particular near high-rise buildings, high wind velocities are often produced at pedestrian level that can be experienced as uncomfortable or even dangerous situations. The wind speed at pedestrian level results from the complex wind flow pattern around a building. Studies of pedestrian wind environment consequently involve the study of building’s aerodynamics in general. Pedestrian comfort in sidewalks, entrances, plazas, and terraces is often an important design parameter that needs to be considered by the building owner and architect. Assessment of the acceptability of the pedestrian-wind environment is desirable during the project design phase so that modifications can be made, if necessary, to improve areas found to be excessively windy. Therefore, the design of a building should not only focus on the building envelope and on providing suitable indoor environment, but should also include the impact of the design on the outdoor environment. The outdoor environment of a building, in particular in terms of wind, has received relatively little attention in the building physics community. Most investigations were based on wind tunnel experiments and the building configuration being most extensively studied is two square-plan building models placed in different relative positions. Earlier studies used rigid models where mean wind pressures and wind forces were measured. Dynamic behaviors are important for tall buildings so that in later studies, wind-induced dynamic response and loading of buildings were investigated. The aim of the present paper is twofold: it is an attempt (1) to stimulate the interest of the building physics community for the problem of wind nuisance around buildings, (2) to indicate the need for further research efforts. The present paper addresses building physicists and focuses on the outdoor wind environment for pedestrians. For this aim, first the typical wind flow pattern around buildings and the related wind environment at pedestrian level are discussed. Second, CFD (Computational Fluid Dynamics) simulations of building aerodynamics have been performed. A numerical model based on the compressible flow equations has been used to simulate the pedestrian wind fields around the programmed tall buildings in Sahand neighborhood located in Eastern Azarbaijan, Iran. Since numerical model can provide the detailed flow field data, it has a great advantage compared with the wind tunnel experiment in evaluating the wind impacts on pedestrian and other environmental issues accurately. By modeling parallel buildings with a passage in between in four different shapes and comparing the results with Beaufort scale, we could improve the wind situation at pedestrian level.