绿洲外围植被防风生态效益的紊流模型

A TURBULENT MODEL FOR ECOLOGICAL EFFECT OF WINDBREAK VEGETATION AROUND THE OASIS

风沙灾害严重地威胁着处于茫茫沙漠中的绿洲，绿洲外围植被则是防御风沙危害的绿色屏障。我们选择位于昆仑山北麓塔克拉玛干沙漠南缘受风沙危害极其严重的策勒绿洲外围植被为研究对象，采用ｋ－ε紊流数学模型，对三种典型植被覆盖度：１８．７５％、３７．５％、５６．３％，七种风速：４、５、６、７、８、９、１０ｍ／ｓ共２１种处理的流场细节进行了模拟。每一处理中以４３２０个数据模拟了ｉ＝１，２，…，１０８，ｊ＝１，２，…，２０，共２１６０个点位在ｕ方向和ｖ方向的速度，由此，找出风沙流通过植被区，在顺流方向随植被盖度变化的递变规律，并定量的反映了绿洲外围植被降低风速、降低进入绿洲沙流量的生态效益。试验表明：顺流方向２ｋｍ厚的植被，盖度由０增至１５％～２０％，可降低风速３７％～４０％；增至３５％～４０％，可降低４８％左右；增至５５％，可降低５４％左右。植被盖度由０增至１５％，３５％，５０％，在地面以上０～２０ｃｍ的高度内，可不同程度地降低沙流量５０％～９０％。

The oasis in the vast desert is disastrously affected by wind- sand flow,while the vegetation around the oasis effectively protects it from invasion. Thus,the research into the ecological effect of the vegetation on the oasis seems especially important. For the reason mentioned above,the velocity field of wind flowing through the vegetation district around the oasis is imitated in this paper by the means of k-εturbulent model with 21 treatments of 3 levels of vegetation coverage:18.75%,37.5%, 56.3%, and 7 1evels of wind speed:4.5.6.7.8.9. 10 m/s. The fieldmeasurement of wind speed was made in the vegetation districts around Qira oasis,located betweennorthern Kumlun Mt. foot and southern edge of the Taklimakan Desert, which is seriously affected bywind-sand flow. In each treatment,the wind speeds of u and v on 2160 points(i= 1,2,…, 108,j=1,2,…, 20) in the velocity field are imitated. Subsequently, the gradually decreasing laws of wind inthe coming direction with the variety of vegetation coverage are made out. The research shows that forthe vegetation of 2 km long in the wind coming direction, when the coverage rises up to 15%～20%from 0 , the wind speed will be reduced by 37%～40%;when it rises up to 35%～40%, and 55%from 0 , the wind speed will be reduced by 40%and 45%respectively. On the other hand , when thevegetation coverage rises to 15%, 35%and 55%from 0 , the sand transport amount at 0～20 cmabove ground surface will be reduced by 50%～90%.