海岸湿沙表面风沙传输特征的风洞实验研究

A Wind Tunnel Experiment of Aeolian Sand Transport over Wetted Coastal Sand Surface

通过湿沙表面风沙传输的风洞实验,研究了湿润海岸风沙流的垂直结构、输沙率随风速与表层湿度的变化规律。输沙测量使用60cm高直立式积沙仪,湿度(M)为沙面表层1mm厚的重量湿度值。结果表明,湿沙表面的输沙量和高度呈指数关系。一般,湿度增大,整体输沙率降低,高湿度床面的沙粒有相对更大的比例被传输到更高的位置。比起低湿度(M<0.587%)沙粒,高湿度(0.587%<M<1.448%)沙粒的垂直运动对湿度变化的影响更加敏感,尤其是在跃移层的底部,当M>1.448%时,输沙率已经很低,小于0.99g.cm-1.s-1。伴随湿度0.587%和1.448%的过渡,风沙流垂向分布被分为3个不同坡度的区域,曲线坡度反映了沙粒间不同水分存在形式的影响差异。对于跃移沙粒,高湿度表面(M>1.448%)仅起到了一个传输平台的作用;当表面变干到某种程度(M=0.587%)之前,表面湿度是跃移运动的主要控制因子,然后风速才重新开始影响输沙。

The change characters of wind-sand flow structure and sand transport rate under different wind speed and different moisture coast were studied in wind tunnel experiments.In the experiment,a standard 60-cm height vertical sand trap was used,and the moisture content was gravimetric moisture content of surface sand within 1-mm thick.Results show that the sand transport profile over the wet surface can be expressed with an exponential equation.Generally,the influence of moisture content on sand transport profile mainly focuses on the bottom of the blowing sand cloud.Meanwhile,the total sand transport drops with the increase of moisture content,and a relatively larger proportion is transported at greater height.The vertical movement of particles over higher moisture surface（0.587%M1.448%） is more sensitive to moisture content variation as compared to those over lower wet surface（M0.587%）,especially,the total sand transport rate tends to be rather low（0.99 g·cm-1·s-1） when M1.448%.The profile of the total sand transport rate varying with moisture content can be divided into three different gradient regions.The gradient of the curve reflects the different influences of the water regime in surface sediments.The higher moisture surface（M1.448%） merely functions as a transport plain for the saltation particles.Surface moisture content is the dominant control factor for saltation activity when the moisture content is in 0.587%-1.448%,and wind velocity will control saltation after the surface dries to the extent of M0.587%.