The wind swirls around buildings due to the turbulence induced by the interaction between the incident air flow and the complex and irregular shape of the structures. This creates areas of low pressure and high pressure that generate whirlwinds and vortices.
When the wind hits a building, it is forced to go around the obstacle and consequently changes direction. Because of this, it often accelerates, compresses against the facades, or divides into different flows. On the sides and at the back, the air forms areas of lower pressure, leading to the creation of turbulence and spiral-shaped vortices. The larger the structure, the more pronounced this effect becomes, often making the surrounding streets very windy or, conversely, surprisingly sheltered. The specific shape of the buildings also influences this: sharp angles and flat facades clearly increase the phenomenon of deflection and the sudden changes in wind speed.
The wind, when it encounters an urban structure, is partially deflected from its initial trajectory. Depending on the size and shape of the buildings, the air slows down or accelerates, creating areas of high pressure on one side and low pressure on the other. This pressure difference forces the air to move quickly around the facades and corners, initiating rapid movements that eventually turn into vortices. These often originate in sharp corners and confined spaces between constructions. As a result, the air swirls chaotically near the buildings, sometimes forming unpredictable gusts at sidewalk level.
The shape and height of buildings directly influence how air moves around them and sometimes facilitate the formation of vortices. If a facade has sharp or irregular angles, air will easily detach in certain areas, creating small turbulence that then grows into larger vortices just behind the building. Similarly, a very tall structure acts as an imposing wall for the wind, forcing it to flow around and above. This bypassing leads to pressure differences, which can create vortex flows downstream that are quite bothersome for pedestrians below. More rounded aerodynamic shapes generally allow for less disturbed air circulation, while buildings with complex or very rectangular shapes significantly increase the formation of these vortex flows close to the ground.
When several buildings are close together in a dense urban area, the wind weaves between them and is forced to accelerate. This creates a corridor effect, with currents that become particularly strong in narrow streets, a phenomenon known as the Venturi effect. When these fast currents encounter angles or other air currents coming from adjacent streets, they spin around and create vortices. These turbulent current areas are often felt at the base of buildings and in open squares, where pedestrians and cyclists can clearly notice this abrupt change. The configuration of the neighborhood, the varying height of the buildings, and their proximity further amplify these effects, potentially turning a simple walk into an unpleasant windy outing.
Aerodynamic engineers often use miniature urban wind tunnels to study and predict how winds will circulate around future buildings in a city.
The curved structure of certain modern skyscrapers, like London’s "Walkie-Talkie," can concentrate the wind and create currents strong enough to unbalance pedestrians at ground level.
In dense urban neighborhoods, the phenomenon known as the "urban canyon effect" amplifies wind speeds. Narrow streets and tall buildings create a funnel effect that accelerates gusts.
Some architects now design their buildings with specific openings or aerodynamic shapes to reduce the formation of disruptive turbulence and enhance the comfort of nearby residents.
In most cases, they can simply be annoying or uncomfortable. That said, very tall or closely spaced buildings can create powerful vortices that make walking more difficult, even dangerous, especially for cyclists, the elderly, or those with reduced mobility.
The complex or irregular geometry of a building can cause unpredictable turbulence and local micro-vortices. These shapes can sometimes dampen certain air currents or, conversely, create areas of sudden wind acceleration.
Yes, that is indeed the case. Tall buildings alter the natural wind trajectories by creating upward or downward currents and can even locally influence temperature and humidity levels. This means they contribute to the creation of urban spaces with their own specific climate.
Yes, various architectural solutions, such as the aerodynamic design of structures, the integration of windbreak elements, the creation of vegetation and green spaces, or strategic spacing between buildings, can significantly mitigate these swirling wind phenomena around urban constructions.
Buildings act as barriers to the flow of air. When a draft reaches a building, it is forced to go around the structure, thus accelerating at the corners and creating stronger winds in those specific areas.
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