横向沙丘气流平均速度变化规律的风洞模拟

 在沙丘动力系统中，存在沙丘形态、气流、沙粒运移三者之间复杂的相互作用。通过风洞实验的方法，针对不同形态的6组横向沙丘模型，采用粒子图像测速系统，测量了模型沙丘周围气流水平速度和垂直速度的变化规律。实验结果表明，横向沙丘迎风坡水平气流存在1.28～1.89之间的加速率，垂直气流存在上扬趋势，这二者均有随沙丘迎风坡坡度增大而增大的趋势。在横向沙丘背风坡，由于气流的分离，水平气流速度减小并出现反向，其大小约为自由风速的17％；垂直气流速度存在下沉趋势，其最大沉速出现在气流重附点附近；背风坡气流速度的变化受沙丘迎风坡坡度影响较小，受自由风速的影响较大。沙丘对气流速度的改变在近地层较为显著，随着高度的增加地形影响逐渐减小。

A Wind Tunnel Simulation on Mean Flow Variances over Transverse Dunes

In an aeolian dune system, the interactions of dune form, airflow and sediment transport are very complex. The changes of wind velocity induced by dune topography, have an important significant in dune dynamics. In this paper, the variations in the horizontal and vertical velocities over 6 different transverse dune models are investigated in a wind tunnel by applying the particle image velocimetry (PIV). According to the experiment results, in the windward of transverse dunes, the increasing horizontal velocity has a speed-up ratio ranged from 1.28 to 1.89, and the ascending vertical velocity has an upwards direction. Both of the horizontal and vertical velocities run higher with the increasing windward slope. In the lee-side of transverse dunes, the horizontal velocity becomes smaller because of airflow separation, and the velocity value in the separation cell is only 17% of free-stream speed. The vertical velocity has a trend of descending, and the maximum sinking velocity is founded near the flow reattachment point. The velocities in the lee-side of transverse dunes are mainly influenced by the free-stream speed but slightly affected by the stoss slope. The results also show that, the change of velocity is significant in the lower portion near dune surface, the higher from the ground, the slighter influence.