Vortex shedding chimney
Vortex Shredding is the phenomenon of alternating low pressure zones at the downside of the structure( tall building) giving rise to a fluctuating force acting at right angles to the wind direction when wind blows across a tall building, vortices are shed alternately from one side to the other. When a vortex forms on the side of a building, it creates a suction force. The force generated by an individual vortex is so large but the potential problem is that vortices tend to form in well-organised patterns and rock the building as they shed alternately from each side. Vortex shredding can cause unwanted movements and damages from fatigue and may leads to damage industrial chimneys. Vortex shredding is responsible for unsteady separation of flow of a fluid around blunt bodies. It leads to a repeating pattern of swirling in fluid dynamics and are known as Karman vortex street.
In low turbulence - Karman street maybe produced in tall building which is uniform along its height. The turbulence produced by many tall structures nearby prevents the formation of coherent vortices. While designing the structures the engineers must be very vigilant in estimating the possible effects of vortex shedding. For monitoring such engineering structures, the efficient measurements of Karman streets can be performed using smart sensing algorithms such as compressive sensing.
To prevent the unwanted vibration of cylindrical bodies, a longitudinal fin longer than the diameter of the cylinder can be fitted on the downstream side to prevent the eddies from interacting and remain attached
In tall buildings, a helical projections resembling large screw threads can be effectively placed at the top to create asymmetric three-dimensional flow and discouraging the alternate shedding of vortices. To prevent the entire building being driven at the same frequency tapering (using variation in the diameter with height) can be used. Even more serious instability can be created in concrete cooling towers, especially when built together in clusters.
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