These graphs show the air velocity reduction effect for different shapes of windbreaks.
The values correspond to the relative reduction (< 1.00) or increase (> 1.00) of the air speed in the vicinity of the windbreak compared to the speed of the incident wind.
They were obtained from wind tunnel simulations during the 1950s.
Windbreaks have many advantages: they reduce the evapotranspiration of the plants they shelter, they preserve the outdoor thermal comfort of pedestrians in winter, they shade and protect crops, they preserve biodiversity in the case of hedges, etc.
Regardless of its shape, these graphs show that the area sheltered by a windbreak is generally equal to 5 times its height.
The positioning of a windbreak must therefore be carefully studied by knowing the direction of the prevailing winds or using modeling tools (CFD).
Recent research shows that the windbreak effect essentially depends on the first third of the height of the windbreak: if this first third is very porous, this effect is almost canceled; if the visual porosity is less, the windbreak effect is retained.
In practice, we consider that the porosity of an effective windbreak must be around 0.2 (20% void).
When will windbreaks become widespread in urban planning?
Sources: V. Olgyay, G. Guyot, J. Gandemer.
Image: V. Olgyay, trans. by C. Gaillard