Studies on the wind in front and back of the shelter-hedges (2)

Abstract

In order to investigate the contrary wind in front and back of shelter-hedges, we used board-fences with interstices of 0%, 20%, 50% and 80%, each being 90cm. high and 15m. long. In case of the hedge with 0% interstice, contrary wind was observed to 0.5 times the height of the hedge (for all the heights of 20cm, 40cm, and 60cm above ground) to the windward, and 9 times the height at the maximum to the leeward of the hedge at 20cm above the surface of the ground. Here it must be noted that the range of contrary wind to the leeward became longer the nearer to the surface. In case of the hedge with 20% interstice, the range was from 2 to 7 times the height, and in case with 50% interstice, the contrary wind was observed only at 20cm above surface ranging from 3 to 7 times the height of the hedge to its leeward, with no other remakable occurrences.The strength of the contrary wind increased according as the interstice became smaller. Wind the interstice of 0%, the velocity of the wind reached 40% of the standard wind velocity to the leeward of the hedge at a distance 3 to 4 times the height of hedge. As the interstice became wider, the spot where the wind is strong, extended to the leeward. The contrary wind lasted for comparatively short time, and in most cases it blew alternately with the normal wind. But, at a distance 3 to 4 times the height to the leeward the wind blew continuously in both cases of 0% and 20% interstices. As the wind velocity increased, the contrary wind also became stronger, but the ratio of its velocity to the normal one scarecely changes. Wide interstice being given, blowing-in caused the increase of wind velocity and at the same time the decrease of contrary wind.