前高后低型防风固沙林防风效应及其对风向的响应

Windproof Efficiency of Shelterbelt in High-low Pattern and Its Response to Wind Directions

[目的]研究由梭梭和柠条组成的前高后低型复合林带的防风效应及其对风向的响应,为荒漠绿洲、沙漠公路、沙漠铁路等防护区人工防风固沙林的营建提供理论依据。[方法]以具有不同个体特征的梭梭和柠条为原型制作仿真植物,配置成前高后低型林带,记作AmBn型,其中,"A"代表仿真植物梭梭,"m"代表其株行距为15cm×40cm,"B"代表仿真植物柠条,"n"代表其株行距为8.5cm×25cm。将其在反方向风作用时记为BnAm型。通过风洞模拟试验,在7,10,15m/s试验风速下,对两种类型林带主要影响区的风速变化、气流加速率和防风效能进行分析。[结果](1)气流到达林带前速度整体降低,到达林带后分化为上(30cm以上)、中(5—20cm)、下(3cm以下)3个特征层,下部气流层在AmBn型和BnAm型林带后的风速恢复点分别位于23和12.5H处。(2)AmBn型林带风影区的范围大于BnAm型林带;两种林带在A,B植物区的冠层高度处各形成一个风影核心区,形成双核模式。(3)在7,10,15m/s试验风速下,AmBn型林带考察区的平均防护效能分别为34.44%,34.98%和32.51%。BnAm型林带考察区的平均防风效能分别为22.62%,19.70%和19.41%。(4)垂直方向上,林带对约1.5H高度范围以下的气流起减速作用,对此范围以上的气流起加速作用;水平方向上,AmBn型林带的防风效能在带前、带中、带后均优于BnAm型林带。[结论]林带的防风效能与两种树种沿风向出现的先后顺序有关,从防护效能和防护距离考虑,建议在防护区外围营建AmBn型林带。

[Objective]To study the windproof efficiency of shelterbelt composed by Haloxylon ammodendron and Caragana korshinskii and its response to wind directions in order to provide theoretical basis for shelterbelt construction on the periphery of desert oasis,desert road and desert railway.[Methods]Prototypes of H.ammodendron and C.korshinskii with different individual characteristics were used to make simulation plants,and then constructed into high-low shelterbelt,which was recorded as AmBn pattern.Here,the capital letter“A”represented the simulated plant H.ammodendron,“m”represented that the planting space was 15 cm×40 cm,the capital letter“B”represented the simulated plant C.korshinskii,and“n”represented that the planting space was 8.5 cm×25 cm.When the wind direction was opposite,the shelterbelt was recorded as BnAm pattern.By the wind tunnel simulation experiments,the airflow field,wind speed acceleration rates and the windproof efficiency were analyzed with the controlled wind speed of 7,10,15 m/s.[Results]①When the airflow reached to the front of the shelterbelt,the wind speed decreased overall.According to the variation intensity of wind speed,the air flow could be divided into 3 layers:the upper layer(above the 30 cm),the middle layer(5-20 cm),and the lower layer(below 3 cm).The speed recover point behind the shelterbelt in AmBn pattern and BnAm pattern was 23 H and 12.5 H,respectively.②The wind shadow range of AmBn pattern was greater than that of BnAm pattern.The wind shadow core areas were formed at the canopy height of both“A”plant and“B”plant,namely,a dicaryon pattern was formed.③Under the controlling wind speed of 7,10,15 m/s,the average windproof efficiency of shelterbelt AmBn was 34.44%,34.98%and 32.51%,respectively.The average windproof efficiency of shelterbelt BnAm was 22.62%,19.70%,19.41%,respectively.④In vertical direction,the forest belt played a role in slowing down the airflow below the height range of about 1.5 H,which accelerated the airflow above this range.In the horizontal direction,the windbreak efficiency of the AmBn type forest belt was better than that of the BnAm type forest belt before,within and after the belt.[Conclusion]The windproof efficiency of shelterbelts is related to the occurrence order of the plants along the wind direction.In view of the protection efficiency and protection distance,the shelterbelt in AmBn pattern is suggested to be constructed.