An ancient Chinese proverb goes like this: When the wind of change blows, some people build walls, and others build windmills.
At first glance, it appears that the DTU scientists have misunderstood this saying; a 30 m long and 3 m tall fence was recently built in front of the wind turbine test sites at the DTU Risø Campus. Upon closer inspection, however, we find that the "wall" is not meant as protection against “change” (or the wind) but as part of an experiment to study how obstacles affect the wind.
The scientists have succeeded in mapping how the fence influences the wind by scanning downwind of the fence with three synchronized Lidars. The data shows how wind direction, fence porosity, and atmospheric stability influence the sheltering effect of the fence. As an example, the figure reveals that the shelter effect can often be observed far downwind of the fence – here, more than 11 fence heights downwind.
The experimental data has been used to improve the shelter model in the software tool WAsP and www.mywindturbine.com. It is available in the DTU report:
Peña, A., Bechmann, A., Conti, D., Angelou, N., & Troen, I. (2015). Shelter models and observations. DTU Wind Energy. (DTU Wind Energy E; No. 00923).
Figure: Average measured wind speed ratio behind the fence. Vectors indicate the magnitude and sign of the ensemble-averaged wind speed. The figure is reproduced from the open access journal Wind Energy Science, 1, 101-114, 2016.
