新月形沙丘表面100cm高度内风沙流输沙量垂直分布函数分段拟合

为研究新月形沙丘表面不同层位风沙流输沙量的垂直分布函数,实测了塔克拉玛干沙漠腹地典型新月形沙丘表面100 cm高度内(以1 cm分隔)的输沙量。分段拟合分析表明:新月形沙丘迎风坡脚输沙量垂直分布规律不完全服从指数函数,出现与戈壁风沙流结构特征相似的"象鼻效应",在0~3 cm区间内输沙量逐渐增大,3cm以上输沙量随高度呈指数函数衰减;沙丘顶部0~10 cm区间输沙量随高度呈指数函数衰减,10 cm以上呈二次函数衰减;沙丘左翼端输沙量随高度呈幂函数分布,沙丘右翼端0~20 cm内以指数函数衰减,20 cm以上呈三次函数衰减;沙丘背风坡脚风沙流输沙量在0~60 cm和60 cm以上分别呈不同形式的三次函数分布。

The Piecewise Fitting of Sand Flux Vertical Distribution of Wind-sand Flow Within 100-cm Height Above the Barchan Dune Surface

In order to study the vertical distribution function of the sand transport rate of wind-sand flow at different height above the barchan dune surface,the sand transport rates of the isolated barchan dune within 100 cm height with 1 cm division in the interior of the Taklimakan Desert were measured.The piecewise fitting results show that: 1) the vertical distribution pattern of sand transport rate at the windward slope base of the dune did not entirely abide by the exponential function but exhibited an"elephant nose effect"similar to the structural characteristics of the wind-sand flow over the Gobi desert surface.The sand transport rate showed a gradually increased trend in the height of 0-3 cm,but above 3 cm it exhibited an exponential function reduction with the height;2) The sand transport rate within 0-10 cm above the dune crest exhibited an exponential function reduction with the height,but above 10 cm it showed a quadratic function reduction;3) The sand transport rate at the left-wing end of the dune showed a power function distribution with the height,but in 0-20 cm at the right-wing end it showed an exponential function reduction and above 20 cm it showed a cubic function reduction;4) The sand transport rate of wind-sand flow in 0-60 cm height and above 60 cm over the leeward slope base of the dune exhibited a different forms of cubic function distribution respectively and the sand transport rate showed a parabola-shaped vertical distribution.both the dune shapes and the dynamic character of the wind-sand flow affected the vertical distribution of the sand transport rate of wind-sand flow over the barchan dune surface.Since the windward slope base and surrounding zone were a net erosion zone,sand grains were coarse and sand supply was relatively insufficient,unsaturated wind-sand flow formed and the increase in sand transport rate with height did not entirely show an exponential function reduction.The distribution of sand transport rate at the ends of the two wings of the dune was asymmetric,this is mainly because the asymmetric shapes resulted in different proportional saltating and suspending sand amounts and the difference in wind velocity pulse in the horizontal and vertical directions.The difference in wind velocity at the leeward slope base and the crest of the barchan dune resulted in eddy flow and caused part of sand particles from the dune crest to deposit at the leeward slope,part of sand particles was transported in suspension and the transport rate gradually increased with increasing height,when the height reached a threhold(determined by both the dune height and the dynamic intensity of wind-sand flow) the sand transport rate reached a maximum value,and then it gradually decreased,exhibiting a parabolic distribution.