A wind tunnel study on wind speed reduction of technical textiles used as windscreen

Abstract

Various technical textiles with different opening sizes, opening size distributions, open areas and flow reduction coefficients were tested in a wind tunnel to compare their efficiency in reducing wind speed. The 10 cm high scaled screens were placed perpendicular to the wind direction at the bottom of the test area of the wind tunnel. A smooth surface turbulent flow with a free wind speed of 6.7 m/s was applied during the tests and the wind speed was measured with vane probes at various locations downwind of the screen. This enables to determine the relative wind speed reduction expressed as a percentage of the free wind speed. All the tested technical textiles with a flow reduction coefficient higher than 60%, which corresponds to a maximum open area of about 60%, create 30% or more wind speed reduction at leeward distances between 5 H and 20 H, and this at all heights between 0.25 H and 1.00 H, with H being the height of the screen. Because of the smooth surface turbulent flow, the wind speed reduction in the leeward flow will be greater than with additional surface roughness. The main objective, however, was the comparison of various technical textiles. The results clearly illustrate that the tighter the material, and hence the smaller the open area, the higher the wind speed reduction in the leeward zones closest to the screen, yet the generated turbulence leeward of too tight materials reduces their effectiveness. Therefore, the flow reduction coefficient of effective windscreens should not exceed 90%, which corresponds to an open area of more than 20%.