Chang Kun, Chen Shengde, Wang Meimei, Xue Xinyu, Lan Yubin
College of Electronic Engineering, College of Artificial Intelligence, South China Agricultural University, Guangzhou, China.
National Center for International Collaboration Research on Precision Agricultural Aviation Pesticides Spraying Technology, South China Agricultural University, Guangzhou, China.
Front Plant Sci. 2023 Jan 26;13:1087636. doi: 10.3389/fpls.2022.1087636. eCollection 2022.
In aerial spraying of plant protection UAVs, the continuous reduction of pesticides is an objective process. Under the condition of constant flight state (speed and altitude), the change of pesticide loading will inevitably lead to the shift of lift force and rotor speed generated by UAV rotor rotation, which will change the distribution of the rotor flow field and affect the effect of aerial spraying operation of plant protection UAV. Therefore, the rotor speed of UAV is taken as the research object in this paper, and the adaptive refinement physical model based on the Lattice Boltzmann Method (LBM) is used to numerically simulate the rotor flow field of the quadrotor plant-protection UAV at different speeds. A high-speed particle image velocimeter (PIV) was used to obtain and verify the motion state of the droplets emitted from the fan nozzle in the rotor flow field at different speeds. The results show that, with the increase of rotor speed, the maximum velocity and vorticity of the wind field under the rotor increase gradually, the top wind speed can reach 13m/s, and the maximum vorticity can reach 589.64 . Moreover, the maximum velocity flow value is mainly concentrated within 1m below the rotor, and the maximum vorticity value is primarily concentrated within 0.5m. However, with the increase of time, the ultimate value of velocity and vorticity decreases due to the appearance of turbulence, and the distribution of velocity and vorticity are symmetrically distributed along the centre line of the fuselage, within the range of (-1m, 1m) in the X direction. It is consistent with the motion state of droplets under the action of the rotor downwash flow field obtained by PIV. The study results are expected to reveal and understand the change law of the rotor flow field of plant protection UAVs with the dynamic change of pesticide loading to provide a theoretical basis for the development of precise spraying operation mode of plant protection UAVs and improve the operation effect.
在植保无人机的航空喷洒作业中，农药用量的持续减少是一个客观过程。在飞行状态（速度和高度）恒定的条件下，农药装载量的变化将不可避免地导致无人机旋翼旋转产生的升力和旋翼转速的改变，进而改变旋翼流场的分布，影响植保无人机航空喷洒作业的效果。因此，本文以无人机的旋翼转速为研究对象，采用基于格子玻尔兹曼方法（LBM）的自适应加密物理模型，对不同转速下四旋翼植保无人机的旋翼流场进行数值模拟。利用高速粒子图像测速仪（PIV）获取并验证了不同转速下旋翼流场中扇形喷头喷出液滴的运动状态。结果表明，随着旋翼转速的增加，旋翼下方风场的最大速度和涡度逐渐增大，顶部风速可达13m/s，最大涡度可达589.64。而且，最大速度流值主要集中在旋翼下方1m范围内，最大涡度值主要集中在0.5m范围内。然而，随着时间的增加，由于湍流的出现，速度和涡度的最终值减小，并且速度和涡度的分布沿机身中心线在X方向（-1m，1m）范围内呈对称分布。这与PIV获得的旋翼下洗流场作用下液滴的运动状态一致。研究结果有望揭示并理解植保无人机旋翼流场随农药装载量动态变化的规律，为植保无人机精准喷洒作业模式的发展提供理论依据，提高作业效果。
