New wind velocity measurement method using a light detection and ranging instrument was conducted. Based on the presented experimental data, the airflow characteristics above a forest were investigated: wind velocity distribution, friction (shear) wind velocity, roughness length, stream lines, drag force, and depth of the boundary layer. The results demonstrated that windward the forest, the boundary layer is shifted and sloped above the forest. Thereby, the fluid streamlines cannot abruptly change direction, as a consequence flat wind velocity profiles, wavy inflected wind velocity profiles, eddies, and flow recirculation were developed; hence, flow separation at a forest ratio x/ h of 2, flow contraction at x/ h of 12, and flow expansion at x/ h of 22 appeared. The shear wind velocity was about 1/10 of the mean wind velocity and the roughness length 1/15 of the forest height. Within a boundary layer depth of about 130 m, the drag force of the forest was 1300 times greater than that of the grass. Behind the forest, the air flow expands and eddies were developed at x/ h of about 7. Passing through the agriculture area and the forest, the physical parameters (turbulent kinetic energy, friction wind velocity, drag force, and depth of the boundary layer) are increasing at the point of roughness increase. To decrease such parameters and to avoid energy and friction losses and damage to trees due to divergence, convergence, separation, and recirculation of airflow, the sharp edge of the forest should be rounded in the range x/ h up to 2. A curved cutting of the front area of the forest may allow to decrease the slope of the boundary layer and the streamlines before, above, and behind the forest and hence lead to a quasi-steady and stable flow with less turbulence, momentum, heat, and mass transfer between the canopy and the atmosphere.
Wind velocity profiles with a blowing sand boundary layer: Theoretical simulation and experimental validation
