海岸风沙流中不同粒径组沙粒的垂向分布模式

通过对河北昌黎黄金海岸沙丘风沙流的野外实地观测与室内风洞模拟实验数据的数值模拟,探讨了我国典型海岸沙丘风沙流中不同粒径组沙粒输沙量的垂向分布模式。结果表明,河北昌黎黄金海岸沙丘表面风沙流中不同粒径组沙粒输沙量的垂向分布特征并不一致,其中细沙和中沙符合典型的指数递减分布规律,但粗沙则为负幂函数分布。究其原因,主要与不同粒径组沙粒输沙量的分布高度及运动方式差异有关。在实际非均匀沙床面上,粗沙主要集中分布于沙丘表面4cm高度内湍流发育的近地表层,运动方式以蠕移为主,沙丘表面湍流的主导作用使其输沙量随高度的变化满足负幂律关系,但中沙和细沙则以跃移运动为主,跃移沙粒输沙量的垂向分布呈现指数递减特征。

Vertical distribution models of sand transport rate of different grain size groups in coastal aeolian mass flux

The vertical distribution model of transport rate of sands in different grain size groups in aeolian mass flux is one of the hot topics on the structure of aeolian mass flux. Some researches have been carried out by use of wind tunnel experiments or mathematical modeling, but the results are different. We believe that the combined methods should be used which include the field observation and wind tunnel experiment as well as mathematical modeling. Changli Gold Coast in Hebei Province is one of the most typical coastal aeolian dune distribution regions in China. It is very famous for the tall and typical coastal transverse ridges in Changli Gold Coast. One of the typical coastal transverse ridges in Changli Gold Coast was chosen to be measured to build the vertical distribution model of sands in different grain size groups in coastal aeolian mass flux by using the combined methods. On the basis of data from field observation and wind tunnel experiment, the vertical distribution model of sand transport rate in different grain size groups in aeolian mass flux, which is the correlation between sand transport rates of different heights with heights in aeolian mass flux, could be obtained by use of mathematical modeling. The results show that the vertical distribution models of sand transport rate in different grain size groups in aeolian mass flux are different. The vertical distribution of coarse sands could be expressed by typical power function, but the vertical distribution of the sand transport rate of medium sands and fine sands could be typically expressed by an exponential function, and the exponential function distribution is their vertical distribution model. Reasons for the difference of vertical distribution models of sands in different grain size groups in aeolian mass flux are the height of distribution of sands of different grain size groups and their movement ways in aeolian mass flux. For coarse sand particles, they are mainly distributed in the scope of 4cm height over dune. Normally turbulent flow plays a leading role in the movement of sands at the low height over dune. The influence of turbulent flow in near-surface layer makes most of the coarse sand particles to move as the way of surface creep and the distribution model of sand transport rate of coarse particles with height to satisfy the negative power relation. But the fine sands and medium sands, they mostly move in the way of saltation. A large number of field observation and wind tunnel experiments as well as numerical simulation research results demonstrate that the vertical distribution of sand transport rate of saltation particles is exponential decrease function.