SE— Structures and Environment: Wind Tunnel Study on Oblique Windscreens

A wind tunnel study was carried out to determine the effect of windscreens obliquely to wind direction on wind speed change and recovery distance at the leeward flow field. Three types of screens, making angles of 90, 60, 45 and 30° with wind direction, were modelled in the tunnel. Screens perpendicular to the wind direction were placed from wall to wall. Since the same screens were placed obliquely, they were not long enough to extend from wall to wall, hence there was a space between screen ends and tunnel walls which was greater, the more oblique the screen was. A free wind speed of 6·7 m s−1 was applied during the tests. Wind speed was measured midway between the tunnel walls with vane probes at various locations downwind of the screen, and for each location at four heights above the bottom surface. One oblique screen making an angle of 45° with the wind direction was extended to the tunnel walls to trace possible differences with the oblique screens which did not normally extend from wall to wall. Hardly any difference in results was found and therefore no further experiments with oblique screens extending to the tunnel walls were carried out. The wind tunnel study illustrates clearly that the effectiveness of windscreens, whatever be the type, decreases with decreasing wind incidence angle, both in percentage wind speed reduction and in recovery distance downwind of the screen.