多层林网与单林带防风效应差异的风洞模拟

Wind tunnel simulation for difference of the protective effect between farmland multiple shelter-nets and single shelterbelt

农田防护林是有效降低作物风沙灾害的重要屏障,而目前防护林研究多围绕单个林带及林网,缺少对多层林网与单林带防风效应差异的整体认识,故本研究选取3种不同行数林带配置(4、6和8行林)3层林网,在3种风速下(8、10和14m/s)进行风洞模拟,研究多层林网与单林带流场及防风效应差异。结果表明:1)林网与单林带流场差异主要表现在林带以上高度,近地面风速差异相对较小。另外,随水平距离增加风速恢复方式不同,林网上下同步恢复,呈平行状;而单林带自上向下逐步恢复,呈阶梯状;2)随着风速增加,单林带防风效应变化较小,林网后略减小,较单林带的效应增量呈减小趋势,在8、10和14 m/s风速下分别为7.99%、3.05%和2.38%。3)4行林林网配置综合防风效应最佳。随着林带行数增加,单林带和林网防风效应均先增大后不变,且林网后多出的效应增量变化趋势也相同,在林带为4、6和8行条件下分别为6.29%、7.99%和7.65%。因此,随着集约化和精准化农业推进,在进行防护林配置时,应从农田林网的整体效应进一步定量,减少林带冗余,实现作物经济效益最大化。

Shelterbelt plays an important role in promoting the stable and high yield of crops by reducing wind speed and sand. However, many researches focused on single shelterbelt （CK） or shelter-nets （SN） solely, and ignored the whole productive effects of multiple SN. In this study, we examined three SN models of different rows configuration （4, 6 and 8 rows）. We subjected these models under wind tunnel simulation with different wind speeds （8, 10, and 14 m/s） to estimate the difference of the wind field and the productive effects between SN and CK. The results showed that the difference of wind field between SN and CK focused on top height of shelterbelt, and little difference existed in ground layer. In addition, there were different ways of wind velocity recovering between SN and CK with horizontal distance increasing. Wind velocity recovering of SN was synchronized in different height; however the wind velocity of CK gradually recovered from top to bottom. With the wind velocity increasing, the productive effects of CK changed less but the productive effects of SN decreased. With the wind velocity increasing, the productive effects of single shelterbelt changes less, but the productive effects of SN decreases. Compared with the single shelterbelt, the increment of productive effects of SN decreased, and the effects were 7.99%, 3.05%, and 2.38% in wind fields with 8, 10, and 14 m/s speeds, respectively. The comprehensive productive effects of four rows SN was the best optimal configuration. The productive effects of CK and SN tended to constant after increase under the increase of the row of shelterbelt, and the increment of the productive effects were 6.29%, 7.99%, and 7.65% in wind fields under 4, 10, and 8 rows, respectively. Thus, with the advance of intensification and precision of agriculture, in order to reduce the shelterbelt redundancy and maximize economic benefits of crops, we should consider the overall effect of SN quantitativly when the shelterbelt is configured.