Wind tunnel simulation of the turbulence in the surface layer

The flow in the atmospheric surface layer is analyzed and discussed with emphasis on those properties which are essential for the prediction of wind loads. Four different flow categories can be recognized which are based primarily on flow observations for various terrain roughness classifications. Simulation of the turbulence is considered to be more essential than simulation of the mean wind profile. Properly conducted boundary layer windtunnel tests need to accommodate the turbulence in each of the four categories, which should also include the small-scale turbulence content in the incident flow. In the case topographic variations control the terrain roughness (complex terrain), current simulation techniques seem to be inadequate.