ABSTRACT
When the wind encounters a façade of a building then the dynamic force of the wind is converted in to a positive or pushing pressure on that façade. At the same time some of the wind is defl ected over and around the building. At the roof and wall edges the air fl ow is accelerated away from the building and creates negative or sucking forces in these areas. Air fl owing down the windward façade reaches the ground and is defl ected upwards where the oncoming wind then spins the air in to a rotating spiral called a vortex. This phenomenon can be experienced when walking towards a tall building – the wind may be behind you as you approach the building but as you get closer you will feel the wind blowing in to your face. Accelerated fl ows at the sides of a building and vortex action at the front of a building can create dangerous conditions for pedestrians. On the leeward or sheltered side of the building (the wake region) there is a much weaker region of negative pressures. Figure 3.2 shows these fl ow features.
