风沙流中沙粒粒度的垂直和水平分布特征

鉴于现有对风沙流中沙粒粒度分布特征的研究很少,本文通过风洞实验,在粗沙和细沙两种床面上、五种风速条件下,采集中垂线垂向集沙及其后水平方向集沙的沙样,并对沙样进行沙粒粒度分析实验。实验结果发现,沙粒粒度频率曲线形态为单峰偏态分布,并与其对应的床面沙粒组成有关。沙粒粒度的平均粒径在垂直方向和水平方向上,均呈指数递减;气流风速越大,平均粒径越大;当风速增加到一定程度时,气流对沙粒平均粒径变化的影响逐渐减小;沙粒在垂直方向上的平均粒径,均大于其对应的床面沙粒平均粒径。沙粒粒度的标准偏差,随着平均粒径的增大而增加。沙粒粒度的偏度系数和平均粒径的相关关系,与其对应的床面沙粒组成有关。由实验结果讨论得出,在非均匀风沙流的沙粒起动中,细颗粒沙粒的平均起跳速度大于粗沙粒,而粗颗粒泥沙的起跳率大于细沙粒。

Vertical and horizontal profiles of grain size in aeolian sand transport

The vertical and horizontal profiles of aeolian mass flux were measured for five different stream velocities in a wind tunnel containing a bed of two mixed test sands,the sand samples of which were further investigated by using a particle size analyzer.Results show that the modal shape of the particle sizefrequency distributions of the saltating sand at different elevations or longitudinal distances are similar to that of the mixed sand in the bed once the boundary layer is fully developed.Mean grain size of size distributions decays exponentially with both vertical height and longitudinal distance and is larger than that of the bed sands.Standard deviation of size distributions increases with mean grain size.Variation of the skewness of size distributions with mean grain size is determined to the size gradation of the bed sands.It is revealed that the mean launch velocity of fine sands is larger than that of coarse sands whereas its dislodgment rate is smaller in the aeolian saltation of non-uniform sand.