敦煌莫高窟顶灌木林带防护效应研究

Sheltering Effect of Shrub Shelterbelt at Top of the Mogao Grottoes

风洞模拟实验和野外观测结果表明,平均林带高H=1 5m,疏透度β=50%的两条灌木林带周围的气流场分为7个能量区。在贴地层,有林带前的拐角绕流阻滞减速区,林带中的灌丛阻挡湍流衰减区,林带后的回流涡旋减速及速度恢复区,林带远方的气流附体加速区。在林带上部,有林带间的阻滞减速区和林带后的涡旋减速区,在林带顶后部有集流加速区。风沙流在阻滞、涡旋回流减速区沉积,而在加速区则会产生风蚀,在林带顶上下层气流交换加强。在低速时林带阻沙能力较强,当风速为10m·s-1时,有林带的输沙量可减少一个量级,即阻滞90%的风沙流;在中高风速时(风速为15m·s-1及以上),林带对风沙流的阻滞作用明显减弱,只阻滞20%。

Both wind tunnel experiment and field observation indicate that the wind regime around two shrub shelterbelts at average 1\^5 m high and with a porosity of about 50% can be separated into 7 energy zones. In the near-surface layer, there are the circumambulating-blocking speed-down zone at the front corner of shelterbelt, the turbulent weakening zone blocked by shrubs inside the belt, the circumfluence whirling speed-down and then speed-up zone behind the belt, and the accelerating zone far away from the belt; In the upper layer, there are the blocking speed-down zone inter-belt, the whirling speed-down zone behind the belt, the conflux accelerating zone just behind the top of shelterbelt. The sands blown by wind accumulate in the speed-down zones while wind erosion occurs in the speed-up zones. The vertical air transfer is intensified at the top of the forest. Shelter forest belt can more effectively hinder blown sand at lower wind speed than at middle-to-higher wind speed, for example, 90% of sand flow has been hindered at 10 m\5s^(-1); whereas, only 20% has been hindered at \{≥15\} m\5s^(-1).