Light floater boards are commonly used in open channel flow studies to reduce free surface disturbances. However, the shear layer generated from the surface of the floaters, which has not been considered in previous research, may have unintended effects, and can alter the downstream flow characteristics. This aspect is investigated using particle image velocimetry at Reynolds number of 35,100 by varying the perturbation caused by the floaters. With the perturbation, the mean velocity profiles show a dip and the Reynolds shear stress becomes negative near the free surface. It is shown that, due to perturbations caused by ejections and sweeps of the inverted shear layer at the floater bottom surface, the joint probability density function of velocity fluctuations near the free surface shifts from ejections and sweeps to outward and inward interactions. The data indicate that the shear penetrates deeper into the flow towards the bed with increase in perturbation.

轻型浮板通常用于明渠流动研究，以减少自由表面干扰。然而，浮子表面产生的剪切层在以前的研究中没有考虑到，可能会产生意想不到的影响，并可能改变下游流动特性。通过改变由漂浮物引起的扰动，使用雷诺数为 35,100 的粒子图像测速仪研究了这一方面。随着扰动，平均速度剖面显示出下降，雷诺剪应力在自由表面附近变为负值。结果表明，由于浮子底面倒剪切层的喷射和扫掠引起的扰动，自由表面附近速度波动的联合概率密度函数从喷射和扫掠转变为向外和向内相互作用。数据表明，随着扰动的增加，剪切更深地渗透到流向床的流动中。