Wind Tunnel Study on Rough and Smooth Surface Turbulent Approach Flow and on Inclined Windscreens

Abstract

The floor of a wind tunnel was provided with isolated roughness elements in the form of small wooden blocks to increase the boundary layer thickness. Since previous experiments were carried out with a smooth floor, the results of the previous research on vertical screens with smooth surface turbulent flow could be compared with the results of the current research on vertical screens with rough surface turbulent flow. It follows that windbreaks are less effective for rough than for smooth turbulent flow, although differences depend on the open area of the windbreak. Furthermore, experiments in the wind tunnel were carried out to compare the effects on wind velocity reduction of vertical and inclined screens. Windscreens were inclined at 30, 45 and 60° with the vertical, either with or against the wind. Except the 30° windward inclined screen with an open area of 49·1% (material C), all other inclined screens were less effective compared with their vertical position, purely through the smaller vertical height of the inclined screens. In general, screens inclined against the wind were more effective than screens inclined with the wind. However, the effectiveness of the windward inclination of the less permeable windbreaks (materials A and B) was more pronounced.