Numerical simulation of agricultural unmanned helicopter corn canopy spraying

Abstract

Plant protection by unmanned aerial vehicle (UAV) is a highly complicated process, especially considering the vast and diversified crop canopy. Furthermore, the droplet dispersal mechanism above and inside the crop canopy remains unclear. Owing to this, the authors used the lattice Boltzmann method (LBM) to simulate the application of plant protection UAV. The LBM is suitable not only to simulate the rotor tip vortex of UAV but also to model the crop canopy with detailed geometry. It is found that the streamwise and spanwise speed of the downwash flow achieve an extreme value both on top of the corn canopy and near the ground. When the droplet diameter decreased from 400 to 50 μm, its deposit region width doubled and its floating time increased from 3 s to more than 12 s. Small droplets are more likely to be lifted by the secondary flow near the ground and drift for a longer distance, while larger droplets are deposited directly. The increase in application height weakened the secondary spanwise flow near the ground and caused less droplet re-lifting and spanwise movement. The best point to initiate and terminate spraying is 2.5 m after passing the target corn canopy region. The droplet penetration rate in the canopy decreased with an increase in droplet size. This study used the LBM to model the unmanned helicopter application on a full corn canopy. Droplet deposition and distribution correspond to droplet size and canopy structure. The simulation results establish a foundation to optimize agricultural aerial spraying in an efficient and methodical manner.