When the unmanned aerial vehicle (UAV) is used for aerial spraying, the downwash airflow generated by the UAV rotor will interact with the crop canopy and form a conical vortex shape in the crop plant. The size of the vortex will directly affect the outcome of the spraying operation. Six one-way spraying were performed by the UAV in a rice field with different but random flying altitude and velocities within the optimal operational range to form different vortex patterns. The spraying reagent was clear water, which was collected by water sensitive paper (WSP), and then the WSP was analyzed to study the droplets deposition effects in different vortex states. The results showed that the formation of the vortex significantly influenced the droplet deposition. To be specific, the droplet deposition amount in the obvious-vortex (OV) state was about 1.5 times of that in the small-scale (SV) vortex state, and 7 times of that in the non-vortex (NV) state. In the OV state, the droplets mainly deposited directly below and on both sides of the route. The deposition amount, coverage rate and droplet size increased from top to bottom of the crops with the deposition amount, coverage rate, and volume median diameter (VMD) ranging 0.204–0.470 μL/cm2, 3.31%-7.41%, and 306–367μm, respectively. In the SV state, droplets mainly deposited in the vortex area directly below the route. The deposition amount in the downwind direction was bigger than that in the upwind direction. The maximum of deposition amount, coverage rate and droplet size were found in the middle layer of the crops, the range are 0.177–0.334μL/cm2, 2.71%-5.30%, 295–370μm, respectively. In the NV state, the droplet mainly performed drifting motion, and the average droplet deposition amount in the downwind non-effective region was 29.4 times of that in the upwind non-effective region and 8.7 times of the effective vortex region directly below the route. The maximum of deposition amount, coverage rate and droplet size appeared in the upper layer of the crop, the range are 0.006–0.132μL/cm2, 0.17%-1.82%, 120–309μm, respectively, and almost no droplet deposited in the middle and lower part of the crop. The coefficient of variation (CV) of the droplet deposition amount was less than 40% in the state of obvious-vortex and small-scale vortex, and the worst penetration appeared in the non-vortex amounting to 65.97%. This work offers a basis for improving the spraying performance of UAV.
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机译：当无人飞行器（UAV）用于空中喷涂时，由UAV转子产生的向下冲洗气流将与农作物冠层相互作用并在农作物中形成圆锥形涡旋形状。旋涡的大小将直接影响喷涂操作的结果。无人机在稻田中进行了六次单向喷洒，在最佳操作范围内具有不同但随机的飞行高度和速度，以形成不同的涡旋模式。喷雾剂是清水，由水敏纸（WSP）收集，然后对WSP进行分析，以研究在不同涡旋状态下液滴的沉积效果。结果表明，涡流的形成显着影响液滴的沉积。具体而言，在明显涡旋（OV）状态下的液滴沉积量是小尺度（SV）涡旋状态下的液滴沉积量的约1.5倍，而在非涡旋（NV）状态下的液滴沉积量的约7倍。在OV状态下，液滴主要沉积在路径的正下方和两侧。作物的沉积量，覆盖率和液滴尺寸从上至下增加，其沉积量，覆盖率和体积中值直径（VMD）为0.204–0.470μL/ cm 2 ，为3.31％分别为-7.41％和306–367μm。在SV状态下，液滴主要沉积在路径正下方的涡流区域中。顺风方向的沉积量大于顺风方向的沉积量。作物中层最大沉积量，覆盖率和液滴尺寸最大，范围分别为0.177-0.334μL/ cm 2 ，2.71％-5.30％，295-370μm。 。在NV状态下，液滴主要进行漂移运动，顺风无效区的平均液滴沉积量是顺风无效区的29.4倍，正下方有效涡流区的平均8.7倍。作物的上层最大沉积量，覆盖率和液滴尺寸最大，范围分别为0.006-0.132μL/ cm 2 ，0.17％-1.82％，120-309μm。而且几乎没有水滴沉积在农作物的中下部。在明显涡旋和小尺度涡旋的状态下，液滴沉积量的变异系数（CV）小于40％，在非涡旋中出现的渗透率最差，为65.97％。这项工作为提高无人机的喷雾性能提供了基础。
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