低覆盖度乔木两种分布格局内风速流场和防风效果风洞实验

低覆盖度植被的防风固沙效果一直是防沙治沙工程中的关键问题。在风速为10 m·s-1和15 m·s-1的风洞实验条件下,模拟研究了覆盖度为20%的行带式分布和随机分布的乔木固沙林的风速流场和防风效果。结果表明:①在水平空间上,随机分布和行带式模式都形成了风影区和风速加速区相互组合的复杂水平流场结构,其中,随机分布要比行带式模式的流场结构更加复杂。②在垂直空间上,林冠下近地面(1.2 cm以下)风速都有微弱的增加,1.6~20 cm高度行带式模式内风速均有所减小,而随机分布模式风速变化无明显规律。③随机分布模式中两株植株相互组合时,不仅在植株两侧出现风速加速区,同时在两植株间出现风速加速区,出现 “狭管增速效应”。

Windbreak Effects and Wind Velocity Flow Field of Low Density Arbor with Two Spatial Distribution Patterns in Wind Tunnel

The sand-fixing and wind-preventing effects of the low density vegetation is all along the key issue in desertification combating engineering. A simulating experiment was conducted to study the wind flow field and wind-preventing effect of arbor sand-fixing forest with the coverage of 20% and in belt or random distributions. The study was carried out in wind tunnel and the experimental wind velocity was 10 m·s~(-1) and 15 m·s~(-1), respectively. The result indicated: ①A complex horizontal wind flow field formed in either the belt and the random distribution patterns, the field structure was composed of the wind shadow and the wind speed acceleration areas. But field structure of the random distribution pattern was more complex than that of the belt distribution pattern. ②For vertical distribution, the wind speed under the canopy (1.2 cm to the ground) increased a little, and that within 1.6～20 cm height decreased in the belt distribution pattern, but the change of wind speed showed no apparent rule in the random distribution pattern. ③When two plants assemble in the random distribution pattern, wind speed acceleration area appeared not only in both sides of the plants but also between the two plants, meaning the "channeling effect of increasing wind velocity."