Look carefully at a flagpole or streetlight on a windy day and you may see the structure oscillating in the breeze. Imagine the phenomenon scaled to the height of an urban skyscraper and you can appreciate that at a minimum, life for the inhabitants on the upper floors would be uncomfortable; and should the building fail due to the forces exerted on it, life would be in peril. How, then, do the designers of tall buildings mitigate against the effect of winds that routinely have velocities of 50-150 km/hr near the tops of tall city buildings? The key phenomena that building engineers need to worry about are the vortices—swirling flows of air—that form on the sides of a building as the wind blows by it and the forces that arise as those vortices form and subsequently detach from the building.
Most people have an intuitive sense of vortices from observations...
