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不同坡度障碍物前气流场特征及其对回涡沙丘形成的影响

, PP. 34-41

Keywords: 回涡沙丘,平均速度,湍流强度,沙丘动力过程,超声风速仪

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Abstract:

?针对布设在腾格里沙漠东南缘的5个不同迎风坡坡度的障碍物模型,采用超声风速仪,在野外实测了障碍物前的气流速度场.气流水平和垂直速度的变化规律表明,障前气流场特征受障碍物迎风坡坡度控制.当迎风坡坡度小于60°时,障前气流以减速和上升运动为主,而当迎风坡坡度大于60°时,障前出现了不同程度的反向气流.水平速度反向区的范围随迎风坡坡度的增大而增大,而垂直速度反向区的范围则随坡度的增大呈变高变窄趋势.受障碍物影响,障前气流表现出可影响沙粒跃移运动的低频高能速度脉动,气流逼近障碍物时,水平和垂直速度湍流强度均增大.距障碍物越近、坡度越大,湍流强度越强.障前气流减速和下沉运动导致风沙流局部过饱和从而发生堆积,这为回涡沙丘的形成提供了物质基础;气流反向不仅影响回涡沙丘的初始发育位置,还是塑造沙丘形态的动力因子.

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