上海市沿海防护林防风效应的风洞试验

Wind Proof Performance of Shanghai Coastal Shelterbelts Tested by Wind Tunnel Experiments

以上海市沿海防护林为研究对象,在实地监测的基础上,配合室内风洞模拟试验,对不同结构的水杉、杨树纯林以及水杉+杨树混交林的防风效应进行测试,结果表明:3种林带的风速沿垂直方向的分布大致相似,为0.9H～2.0H,风速廓线较为倾斜;而在2.0H～4.0H,风速廓线接近垂直;接近地面的薄层内,风速廓线接近水平。3种林带的风速沿水平方向的分布也大致相似,气流经林带阻挡,大部分偏离原来流线,从林带上部区域流过,只有少部分气流穿过林带而使风速降低。在疏透度为40%的条件下,随着风向与林带夹角正弦值的增大,使风速降低30%的有效防护距离显著增大。

Taking the coastal plantations of Shanghai as study object,the wind proof performance of the different structured shelterbelts of Cunninghamia lanceolata pure stands,Populus spp.pure stands and the mixed stands composed of Cunninghamia lanceolata and Populus spp.was tested by combining the field monitoring with wind tunnel simulation.The results showed that the vertical distribution of the wind velocity on the lee side of the 3 types of shelterbelts was similar.The wind profile was declined within 0.9 H-2.0 H distance,whereas the wind profile tended to be vertical within 2.0 H-4.0 H distance.The wind profile close to the ground surface was almost horizontal.The horizontal distribution of the wind velocity on the lee side of the 3 types of shelterbelts was also similar.A large proportion of the wind air flow changed its original route when it was blocked by the shelterbelts and then flew over the plantations,and the little proportion of the air flow penetrated the shelterbelts and its flow speed was consequently reduced.When the density of the shelterbelts was 40%,the effective protection distance within which the wind speed could be reduced by 30% would be significantly increased along with the increment of the sine value of the angle between the wind direction and the shelterbelts.