不同带宽的防风固沙林流场结构及防风效能风洞实验

Wind Flow Field and Windproof Efficiency of Shelterbelt in Different Width

林带宽度是防风固沙林建植时要考虑的基本参数,研究不同带宽林带的防护效果对防风固沙林配置及构建具有重要的指导意义。通过风洞模拟实验,在7、10、15 m·s^(-1)风速条件下,对单行一带(Ⅰ型)、三行一带(Ⅱ型)、六行一带(Ⅲ型)和九行一带(Ⅳ型)共4种带宽的林带的迎风面、带中和背风面的风速进行了测定,分析了4种林带的风速流场、风速加速率和防风效果。结果表明:(1) 4种林带流场结构和垂直风速变化规律相似,沿来风向均形成了林带上方和迎风面林缘附近的小范围高风速区及其后的风影区相互组合的流场结构;依据风速垂直变化规律划分为上部变化层(高度30～60 cm,受林带的影响最小)、中间变化层(高度5～20 cm,风速受林冠遮蔽作用,影响最大,且为风影区形成层)和近床面变化层(高度1～3 cm)。(2) 4种林带在垂直纵剖面上的平均风速加速率随林带宽度的增大而减小,即Ⅰ型(0. 90)>Ⅱ型(0. 87)>Ⅲ型(0. 79)>Ⅳ型(0. 78)。(3) 4种林带的防风效果为Ⅰ型和Ⅱ型林带相同,Ⅲ型和Ⅳ型林带相同,后2种林带的防风效果优于前2种林带,且4种林带的防风效能均随着风速的增大而减小。

The width of shelterbelt is the basic parameter to be considered at building the windbreak and sandbreak forest. It has important directive significance to study the protective effect of different width of shelterbelt on the configuration and construction of the windbreak and sandbreak forest. In order to compare the ~nd speed field, wind speed acceleration and windbreak effect of shelterbelt in different width. We studied the change of the vertical space wind velocities in the condition of 7, 10 and 15 m·s-1 under the wind tunnel. The result showed that： （ 1 ） Four kinds of shelterbelt have similarity in the flow field structure and the change of vertical wind speed. It was found that four kinds of forest belt formed flow field structure which was combined by the high wind speed area and the wind shadow; We divided the vertical space into three layers according to the change of vertical wind speed： upper change layer （30-50 cm, it was least affected by the forest）, the middle change layer （5-20 cm, it was the greatest affected by the forest） and near bed surface change layer （1-3 cm）. （2） The acceleration rate of wind velocity decreased with the increase of the width of shelterbelt. It is type Ⅰ 〉type Ⅱ 〉type Ⅲ 〉type IV. （3） The windbreak effect of the four kinds of forest belts is the same type I and type Ⅱ, the same type Ⅲ and type Ⅳ. The windbreak effect of the latter two kinds of forest belts was higher than the former two kinds of forest belts. The windbreak efficiency of the four forest belts decreased with the increase of wind speed.