风沙流中不同粒径组沙粒的输沙量垂向分布实验研究

Vertical Mass Flux Profiles of Different Grain Size Groups in Aeolian Sand Transport

在非均匀沙床面上,风沙流中不同粒径组沙粒的输沙量垂向分布,是非均匀风沙运动研究的重点。研究首先通过风洞实验,收集了风洞中垂线垂向输沙量分布沙样,然后对集沙沙样进行了沙粒粒度分析实验,实验分析结果得出了不同粒径组沙粒的输沙量垂向分布规律,基于稳定平衡风沙跃移运动模型和本文实验结果,最后数值模拟研究了不同粒径组沙粒输沙量垂向分布,与沙粒起跳速度和角度之间的关系。本文研究结果得出,在非均匀风沙流中,粗粒径组沙粒垂向输沙量上部符合指数递减分布但近床面区偏离指数分布,呈现为偏大型分布,粗粒径组对应的沙粒起跳速度和角度分布均为指数函数;细粒径组沙粒垂向输沙量在整个高度上均符合指数递减规律,细粒径组沙粒对应的起跳速度分布为指数函数,起跳角度分布为高斯函数。沙粒的平均起跳速度,在0.4u*～2.2u*之间变化,随着气流风速(u*)和沙粒粒径的增加而减小。

This paper presented the vertical mass flux profiles of different grain size groups in aeolian sand transport, which is the hot issue of non-uniform sand transport research but is rarely studied recently. The sand samples of vertical mass flux were further investigated using a particle size analyzer that were measured in a wind tunnel experiment conducting with non-uniform sands and five different stream velocities. Results show that the vertical mass flux profiles of coarse sand groups are similar to that of all sands measured in the wind tunnel, exhibiting an exponential decay distribution with a positive deviation occurring in the near-bed region; however, the vertical mass flux profiles of fine sand groups decayed exponentially in the whole height. Based on the results above, this study simulated the vertical mass flux profiles of different grain size groups in terms of equilibrium saltation theory. It is revealed that in the non-uniform sand transport, the launch speed and angle distributions of coarse sand are exponential function; the launch speed of fine sand is exponential function but the launch angle of it is Gaussian function. The mean sand launch speed occur between 0.4u＊ and 2.2u＊, decaying with the increase of wind speed （u＊） and grain size.