An experimental study of the airflow over a hill in the atmospheric boundary layer

Between 1975 and 1977, the Centre Scientifique et Technique du Bâtiment (CSTB) carried out a study of the overspeed effect over a hill in the surface boundary layer. The hill in question was situated in open country and had a drop of about 100 m for an average slope of 8%. The experimental equipment consisted of three 25 m high masts placed along the upwind slope of the hill. Each mast was equipped with four Gill Propeller anemometers. The data set analyzed consisted of 65 recordings of strong winds which had an average velocity greater than 6 m s-1.Near the ground, local topographic effects and inhomogeneous roughness along the slope have the same influence on the overspeed effect as the mean slope of the hill. The overspeed is proportional to the upwind slope, but on the other hand, the turbulence structure does not seem to be disturbed by the hill.

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