单条林带防护作用区风速分布特征

Characteristics of windspeed distribution affected by a single shelterbelt

为了揭示防护林带对旷野风速运动变化所产生的作用，通过空间多点观测，来研究单条林带防护作用区风速分布特征。结果表明，林带背风面2．5～19H范围内形成的风速降低区，是林带主要保护区和作用范围。其中，4～13H区域内由旷野最大风速值6．4m／s降低至2．7～5．0m/s，风速降低幅度为29．7％～57．8％；13～19日区域内风速分布为5．0～6．0m／s，降低约6．3％～21．9％。在林带迎风面3．5H范围内形成的次降风区，风速降低了0．4～1．0m／s；林带附近乱流交换比较强烈，而且在林带两端处略偏向林带背风面有两个较大的动力速度增强区，风速超过7.0m／s，甚至达到7．5m／s。在林带的垂直方向不同区间的垂线上风述变化不同，林带的有效防护距离并不完全相同。据此提出林带“有效防护面积”的新概念，是表征单条林带防护作用火小的客观指标，能准确地表达农田防护林带的防护区域范围和防护程度。

Through special multi-point investigation in the field, the characteristics of windspeed distribution affected by a single shelterbelt is discovered to study the effect and influence of shelterbelt on windspeed near the shelterbelt windward and leeward. The results show that, the whole protection area is composed of primary area leeward shelterbelt from 2.5H to 19H and second area windward shelterbelt within 3.5H. In the primary area, windspeed is about 2.7～5.0m/s in the range of 4～13H and 5.0～6.0m/s in the range of 13～19H. The degree of windspeed decreased from 6.4m/s in the field without shelter is 29.7～57.8% and 6.3～21.9% in the range of 4～13H and 13～19H, respectively. In the second area, windspeed abatement is some 0.4～1.0m/s within 3.5H. The turbulent areas come forward in the vicinity of the shelterbelt. Two windspeed-increase-areas come into being at the end of shelterbelt slightly leeward shelterbelt, and windspeed is about 7.0N7.5m/s in turbulent areas. Furthermore, the ＂effective protection distances＂ are different among every vertical line to the shelterbelt. On the basis of this result, a new concept of ＂effective protection area＂, defined as function of shelterbelt length and effective protection distance, has been put forward to precisely express the protection effect.