The instantaneous variation of sand concentration entrained by unsteady wind was investigated experimentally by high-speed photography.CMOS high-speed digital camera was adopted to record transport instantly,and specific particle identification method was introduced to count particle number of images.Series of sand concentration were obtained accordingly while the time-averaged wind velocity increased linearly.Also,wind velocity at the top point of the saltation layer and main flow velocity were measured simultaneously by hot-wire anemometer equipped with hot-film probe.The results confirmed that the sand concentration during the transport was always unsteady with 100Hz fluctuated frequency at least.The interaction between the sand and the wind had lagging effect.The effect of atmospheric turbulence on sand concentration depended directly on the sand size.While the sand size was not larger than 160μm,tiny change of the wind velocity would cause the fluctuation of sand concentration with larger amplitude.The fluctuation of sand concentration was highly correlated with the change of the wind velocity.For large sized sand,such as 300-500μm,only larger amplitude changes of wind velocity in long time could bring the obvious fluctuations of the sand concentration.Therefore,the sand concentration would be determined by the time-averaged wind velocity.%在大气边界层风洞内采用高速CMOS相机记录了时均风速线性上升的来流条件下运动沙粒的图像.根据二进制图像标记像素的连通性,从数字图像中提取相机拍摄区域内沙粒的数量N,由此计算得到风沙流的瞬时含沙量C.获取图像的同时,使用恒温式热线风速仪MiniCTA配合55R49热膜探头测量观测域上方主流位置和跃移层顶部附近的风速变化.实验结果表明,风沙流中的瞬时含沙量总是非稳定的,其变化频率至少在100Hz以上.风沙之间的相互作用存在一定的滞后效应,大气湍流脉动对含沙量的作用与沙粒粒径相关,粒径越小,风速脉动作用越大.当粒径≤160μm时,风速的微小变化即可引起含沙量的明显波动,二者高度相关.当粒径较大的时候,如300～500μm,只有较长时间较大幅度的风速脉动才能使含沙量有较大幅度的变化,研究时均风速变化对含沙量的影响更具有意义.
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