低覆盖度下两种行带式固沙林内风速流场和防风效果

研究在风速为10m/s和15m/s的风洞实验条件下,覆盖度为20%和25%的单行一带和两行一带模式乔木固沙林内的水平和垂直空间的风速变化情况,达到对两种不同模式的风速流场和防风效果进行比较分析的目的。通过分析得出:两种配置模式都形成了风影区和风速加速区相互组合的复杂的水平流场结构。两种模式对垂直空间风速影响相近,根据对不同高度风速的不同影响划分为微变化层(20-35 cm)、显著变化层(6-12 cm)和稳定变化层(0.4-3 cm)层次,两种模式在这几个层次风速表现出相同的变化规律。两行一带模式在第一带前降低水平空间风速的效果低于单行一带模式,第一带后高于后者。降低垂直空间风速规律为:对0.4-50 cm高度的风速均有一定的降低作用,0.4-12 cm高度的风速的降低效果较显著,且两行一带模式降低近地表(0.4 cm)风速的效果要高于单行一带模式。

Wind velocity field and windbreak effects in two types of low density and belt-scheme sand-break forests

For comparing wind velocity field and windbreak effects between the one-line-one-belt (OLOB) and two-lines-one-belt (TLOB) schemes of sand-break forests, we studied horizontal and vertical profiles of wind velocity field of the two schemes at 20% and 25% cover under simulated wind speeds of 10 and 15 m/s. It was found that in both schemes there was a complex horizontal flow field comprising wind shadows and acceleration areas. The two schemes showed similar effects on the vertical profile of wind speed. We divided the vertical space into three layers according to the different effects on vertical wind speeds: the layer with slight change (20 to 35 cm above the ground), the layer with significant change (6 to 12 cm above the ground), and the layer with steady change (0.4 to 3cm above the ground). For each of the layers, the two schemes displayed the same pattern of variation. The TLOB was less effective in reducing horizontal wind speed than the OLOB before the first belt, but the former was more effective after the first belt. The observed patterns of reduced vertical wind speed were such that wind speed was reduced at 0.4 to 50cm above the ground, with the reduction being more apparent at 0.4 to 12cm, and that the TLOB was more effective in reducing wind speed near ground surface (0.4cm) than the OLOB.