植保无人机下洗气流对作物冠层作用规律研究

Effect of Plant Protection UAVs Downwash on Crop Canopy

植保无人机作业过程中,旋翼下洗气流不仅会对雾滴沉积效果产生影响,还会对作物冠层产生扰动作用。揭示冠层扰动区域的特点,有助于理解无人机作业特征,可为优化雾滴沉积效果和施药系统提供理论依据。本文通过航拍方法和机器视觉技术研究了无人机下洗气流对作物冠层的影响。结果表明:单旋翼和多旋翼无人机下洗气流所引起的作物冠层扰动区域特征有明显差异。悬停时,单旋翼无人机的冠层扰动区域呈环状,面积较大;多旋翼无人机呈圆形,面积较小。作业时,因受机身不对称结构影响,单旋翼无人机前进和倒退两种飞行姿态的冠层扰动区域特征有所不同,前进时,冠层扰动区域面积小且不规则,倒退时,扰动区域面积较大且呈U状分布包裹机头;多旋翼无人机2种飞行姿态下冠层扰动区域面积和形状基本一致。作业速度对冠层扰动区域特征有显著影响。速度低时,扰动区域较为集中,呈近似椭圆形分布,植株摆动剧烈;速度高时,下洗气流扫掠而过,扰动区域呈长条状分布,植株摆动很小。当P20型植保无人机速度为3、4、5、6 m/s时,冠层扰动区域平均滞后距离分别为1.77、2.71、3.61、4.31 m。扰动区域滞后距离和无人机飞行速度成正比,对两者关系进行回归分析,得出决定系数R^2为0.8754。此外,速度越大,下洗气流对自然风的抵抗作用越弱,冠层扰动区域位置不稳定,不利于抑制雾滴漂移。

During the spraying application of plant protection UAV,the rotor downwash will not only affect the droplet deposition,but also cause disturbance to the crop canopy.Revealing the characteristics of the canopy disturbing area is helpful to understand the application characteristics of the UAV,and can also provide a theoretical basis for optimizing the droplet deposition effect and the UAV spraying system.The effects of UAVs downwash on crop canopy were studied by the methods of aerial photography and machine vision technology.The results showed that there were significant differences in the characteristics of the crop canopy disturbing area caused by the single-rotor and multi-rotor UAVs downwash.Under a hovering situation the single-rotor UAV had a ring-shaped disturbing area with a large size,the multi-rotor UAV had a circular shape with a small size.Due to the influence of the asymmetrical structure of the UAV body,the disturbing area characteristics for the forward and backward movement attitudes of the single-rotor UAV were different.When advancing,this area was small and irregular,while moving backward it was large and distributed in a U-shape.Under the two flight modes,the multi-rotor UAV was basically the same in terms of size and shape of canopy disturbing area.Moreover,the flight speed had a significant effect on the characteristics of the canopy disturbing area.When UAV flying with a low speed,this area was more concentrated with a nearly circular distribution,and the plants were swung heavily;when operating with a high speed,the downwash was swept over crop canopy and the disturbing area was distributed in a strip shape,and the plants were swung lightly.As for the P20 plant protection UAV,when the flight speed was increased from 3 m/s to 6 m/s,the average lag distance of the canopy disturbing area was 1.77 m,2.71 m,3.61 m and 4.31 m,respectively.The lag distance of disturbing area was proportional to the flight speed of the UAV.In addition,the faster the speed was,the weaker the resistance of the downwash was to natural wind,which was not conducive to contain the droplets drift,and the position of the canopy disturbing area was unstable.Based on the research results,it was pointed out that plant protection UAV rotor downwash can only effectively promote the droplet penetration under the premise of the low operating speed and the overlap of the position for droplet deposition and canopy disturbing area.