Wind Dynamics Essay

958 Words 4 Pages
Wind is the result of fast blowing air. It carries kinetic energy with it, and has the capability to cause destruction of the objects that causes obstruction. The force of the wind exerts pressure on any object it comes across. The variation of this pressure has varying effects on types of objects. According to aero-dynamics, the objects which come across the wind are classified as bluff bodies and stream-lined bodies. Bluff bodies are the ones with sharp edges and regular geometrical features. Stream-lined bodies are the ones which have a definite stream-line shape.
Wind being a fluid, behaves differently when it strikes either type of bodies. As the wind strikes the stream-line bodies, it glides across the surface, and follows a laminar
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This gives rise to turbulent flows and varying pressures. As the wind passes past a bluff body, it undergoes boundary layer separation, which causes imbalance in pressure. This results in a phenomena, specific to bluff bodies, called the vortex shedding. The wind leaving the body, which undergoes vortex shedding causes alternating wind pressures at the rear end of the body. This alternating pressure forces the body to sway to and fro respectively. If the oscillating frequency matches with the rear natural frequency of the building, it leads to resonance effect, which is matter of serious concern.
The knowledge on vortex shedding effect on bluff bodies throws light on the design of geometry of the buildings (Kim et al., 2014). Although it is exceptionally ideal to have stream lined buildings, it is pragmatically not possible. But, certain measures can be taken to minimize the effect of vortex shedding on structures. Vortex shedding effect on a building exerts a force on it, in all directions, including the along-wind direction and across-wind direction. These forces are responsible for causing the over-turning moment in the
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The speed of the wind and its other properties vary with height. Hence, their effect on tall buildings fall into different category. Turbulence is a property of the wind, when the wind is not in laminar flow. The wind in chaos is turbulence. The literature reveals that turbulence depends on the boundary condition through which the wind flows. The surface nature through which it flows sets the wind flow pattern. If the wind blows through rough terrain, then it is set into turbulence. It can also be a result, if the blowing wind encounters multiple obstacles in its path. Turbulence is correspondingly a function of height (Cermak, 1976). The atmosphere close to the ground surface poses multiple obstructions, hence higher turbulence intensity. As we go higher in the atmosphere, the surface obstructions reduce, and hence the turbulence reduces. This sets the wind to coherence, which induces the vortex shedding. Hence, as the structures’ height increases, their vulnerability to adverse effects of wind increases. To prevent this phenomena, structural modifications which introduces turbulence have to be incorporated. Design of asymmetrical plans, balconies designed in the corners of buildings, facility for air-holes, etc. (Irwin, 2008). These modifications breaks the wind pattern, thereby reducing the possibility of strong vortex forces. The tall structures amidst several structures

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