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Pedestrian-level wind environment around buildings--with special reference to the effects of building dimensions, building separation and podium structure

Authors Tsang, Chun Wang
Issue Date 2009
Summary Hong Kong is one of the most densely populated cities in the world. High density living has the advantages of efficient land use and public transport utilization, and optimal use of other infrastructure and public utilities. On the other hand, this characteristic leads to congested building designs and urban development in the past which adversely affect our lives in many aspects. Therefore, in recent years, urban renewal projects are held all over the place in Hong Kong. Due to the significant changes of building forms, awareness and concerns are raised by the communities on how the newly built structures alternating the surrounded wind environments. Studies are needed to evaluate the wind environments around these high-rise buildings and identify the potential problematic areas. This research aims at investigating the wind environments around building by means of physical simulation – wind tunnel modeling. Isolated building group was modeled in a wind tunnel under a sub-urban terrain wind flow characteristics. Different building configurations were modeled, including single building, a pair of buildings, a row of four buildings and podium structures, to investigate the effects of building dimension, building separation and podium on the surrounded pedestrian-level wind environments. In the wind tunnel simulation, Irwin Sensor was re-fabricated to measurement the wind speeds at the pedestrian level of the surrounded environment. The re-fabricated sensor was calibrated and showed good agreements with the measurements of a hotwire anemometer. The frequency response, interference effects, noise-to-signal ratio and resolutions of the Irwin Sensor have also been characterized which indicated that this sensor is suitable for pedestrian level wind speed measurements for this research. Mean wind speed and Gust Equivalent Mean (GEM) wind speed were analyzed from the measurements to evaluate the natural air ventilation and pedestrian wind comfort issues at the surrounding environment respectively. In terms of natural air ventilation, the general features of the low wind speed areas around buildings were identified. The extents of the low wind speed areas were sometimes more than 4 building height at the downstream side of the buildings. It was found that a wide building is not favorable for air ventilation. Detrimental effects were also observed in a podium structure. On the other hand, a tall building would improve the ventilation by re-directing the upper level wind to the ground. In the investigation of gap width effects between buildings, it was found that the wind movement at the back of the building is governed by the interaction between two opposite flows – the backflow created by the vertical recirculation and the flow passing through the building gaps. From these results, it is suggested that the separation between buildings should be zero or very large, close to one building width, in order to induce reasonable wind movement for ventilation purposes. For pedestrian comfort concerns, it was found that a building with larger front area would potentially create a worse wind conditions for human activities. Besides, for the same front area buildings, a greater height to width ratio configuration would induce a poor wind condition. To solve discomfort issues, it is generally believed that the podium can protect the pedestrian from the strong wind created by the downwash effect. This research proved that the maximum wind speedsaround the buildings were maintained at similar magitudes. In addition, the podium structure enlarged the uncomfortable area which potentially affects more people in the surrounded environments.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2009
Language English
Format Thesis
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