Wind tunnel observations about the shelter effect of porous fences on the sand particle movements

The effect of porous wind fences on the wind erosion of small sand particles from a two-dimensional triangular prism pile of sand was investigated experimentally. The mean velocity and turbulence intensity profiles measured at the sand pile location were simulated to fit to the atmospheric boundary layer over open terrain. Flow visualization was carried out to qualitatively determine the movement of the wind-blown sand particles. In addition, the threshold velocity was measured using a digital image processing system at a range of values of the fence porosity epsilon, particle size D-p and sand pile height h. As a result, various types of particle motion were observed according to the experimental conditions. The fence of porosity epsilon = 30% was found to have the highest threshold velocity, indicating a good shelter effect for abating wind-blown sand particles. The threshold velocity was found to increase with increasing sand particle diameter. The threshold velocity was also enhanced when the height of the sand pile was lower than the fence height. (C) 2002 Elsevier Science Ltd. All rights reserved.