B1.1 Physical Fundamentals of Natural Wind

The atmospheric boundary layer is a key characteristic of natural wind. It is defined by an increase in wind speed (from zero at the ground) and a decrease in turbulence intensity with increasing height, as shown in Figure 1. For the measurement of mechanical quantities on structures, replicating this boundary layer is essential. Typical strong winds exhibit neutral thermal stratification, where temperature and pressure variations with height are negligible for most practical applications. Accurately describing a natural boundary layer requires defining specific parameters and conditions.

The atmospheric boundary layer is divided into the viscous sublayer, the Prandtl layer, and the Ekman layer, as shown in Figure 1. While the viscous sublayer is usually irrelevant for numerical modeling, the friction-dominated Prandtl layer extends up to approximately 100 meters in height. In the Ekman layer above, the wind veers toward the direction of the geostrophic wind. The simulation of atmospheric wind flows often neglects the Coriolis force, which is considered conservative for most wind engineering applications.

Atmospheric Layer Stratification and Characteristics of Boundary Layer According to Koss [7]