Numerical simulation and spray test validation of the downwash airflow field for thermal fogging protection UAV

Aiming at the problem that the traditional plant protection UAV has poor droplet penetration due to the tall plants and overlapping leaves after the closure of maize in the middle and late stages, which leads to the difficulty of disease and pest control, this study combined the thermal atomization technology of pulsed smoke machine with the efficient plant protection UAV to design a smoke plant protection UAV that can meet the disease and pest control of maize and other densely planted tall stalk crops in the middle and late stages. A computational fluid dynamics method based on the Lattice Boltzmann Method (LBM) was used to numerically simulate the downwash airflow field of a smoke plant protection UAV (six-rotor) to explore the variation characteristics of the rotor flow field in different flight directions, at different flight speeds and at different flight times. The results show that: When the flight height of the UAV is 4 m and the flight speed is 2-5 m/s, with the increase of the speed, two distinct tail vortices gradually form behind the fuselage, and the height and diffusion distance of the tail vortices also increase with the increase of the speed. In addition, with the increase of the flight speed, the amount of droplets drifting up and to both sides will increase, and the intensity of the left side is greater than that of the right side. This can guide the nozzle position adjustment. The droplet deposition and diffusion distribution data of the smoke plant protection UAV were measured without plant cover through field test, The results showed that the median diameter of the droplet volume at each test point was about 50 μm, and the particle size range of the droplets met the requirements for the prevention and control of plant diseases and insect pests. The spatial distribution of droplets increased from top to bottom, and the trend of each layer in the horizontal direction was about the same, and at the same height and spray flow, the droplet particle size and sedimentation decreased with the increase of flight speed.