八旋翼植保无人机下洗气流对雾滴运动与分布特性的影响

Effect of downwash airflow of 8-rotor unmanned aerial vehicle on droplet motion and spatial distribution

多旋翼无人机由于其质量轻、操作灵活、飞行稳定等优势,已成为中国植保无人机市场上的主流机型。为探究多旋翼无人机旋翼气流分布特性及其对雾滴运动和沉积行为的影响,本文基于大疆MG-1P型八旋翼植保无人机的下洗气流场进行测定,并对比分析了旋翼气流对喷雾雾滴的速度、粒径和沉积分布均匀性的影响。结果表明,无人机旋翼下洗气流的强度伴随测试层高度的下降而降低,机体正下方的气流速度方向近似于竖直向下且呈现先增加后减小的趋势,位于机体两侧区域的气流呈现“先收缩、后扩张”的喇叭状,近地位置测试点L和M的气流方向均指向测试区域外侧斜下方,其与竖直方向的夹角分别为71.3°和81.5°。整体而言,无人机机身两侧旋翼下洗气流的速度和方向呈对称分布。在旋翼静止时,喷雾雾滴的沉降速度较慢,各测试层及测试点的雾滴速度均低于1 m/s。无人机悬停时,其旋翼风场极大地提高了雾滴速度,且雾滴速度分布特性与旋翼风场强度高度吻合。与旋翼静止相比,无人机悬停时产生的高速下洗气流可致使雾滴粒径增大。雾滴的沉积分布效果在距离地面20 cm处最好,其在旋翼静止和悬停条件下的平均沉积量分别为4.69μL/cm^(2)和5.85μL/cm^(2),沉积量的变异系数分别为51.81%和36.87%。无人机旋翼下洗气流可有效提高喷雾雾滴的沉积量和分布均匀性。本研究可对多旋翼植保无人机下洗气流优化、雾流场与气流场的耦合以及提高喷雾液的利用率和分布均匀性提供参考。

To explore the downwash airflow distribution characteristics of the multi-rotor unmanned aerial vehicle(UAV)and its influence on droplets movement and deposition,the spraying comparison experiment between static-state spray and hovering-state spray was carried out with DJI MG-1P eightrotor plant protection UAV.The results showed that the strength of the downwash airflow of the UAV decreased with the height of the test layer;the direction of the airflow velocity directly under the UAV was almost the vertically downward direction,and was characterized by increase first and then decrease.The airflow on both sides of UAV presented as a“contracts first and then expands”horn shape,the airflow directions of the test points L and M near the ground were outward obliquely with angles in the vertical direction of 71.3°and 81.5°,respectively.In general,the velocity and direction of the downwash airflow on both sides of the UAV were symmetrically distributed.In the static-state spray,the settling velocity of droplets was slow and the droplet velocities of the test points in each test layer were all lower than 1 m/s.While,in the hovering-state spray,the wind field formed by rotors greatly improved the droplet velocity,and the droplet velocity distribution was highly consistent with the airflow field strength.Compared with the static-state spray,the high-speed downwash flow generated by the rotors in the hovering-state spray increased droplet size.The best deposition droplets distribution effect could be seen at a height of 20 cm from the ground,with the average deposition amount and the coefficient of variation(CV)of 4.69μL/cm^(2) and 51.81%in static-state spray,and 5.85μL/cm^(2) and 36.87%in hovering-state spray,respectively.Correspondingly,the downwash airflow of the UAV could effectively improve the deposition amount and distribution uniformity of droplets.This study give a reference for the optimization of downwash airflow,the coupling of droplet-airflow field,the improvement of the utilization rate and distribution uniformity of spraying for multi-rotor plant protection UAVs.