Investigating the Pesticide Spraying Characteristics of Plant Protection UAV and Designing a Variable Spraying System for Improving the Spraying Uniformity

Application of pesticide has become an essential management practice in modern agriculture. However, due to the limitations in available pesticide application technologies, control of some pests has become challenging. Recently, multirotor unmanned aerial vehicle (UAV) has become a popular tool in pesticide spraying due to the ability of creating downwash airflow by the rotation speed of the rotor. In this study, the effect of downwash airflow of plant protection UAV was simulated using the computational fluid dynamics (CFD) method in ANSYS software under different spraying conditions. As the second step of the study, a variable spraying system (VSS) was developed to increase the efficiency of plant protection UAV based on pulse width modulation. According to the CFD simulations, at the position of 0.3 m and 2 m below the UAV, the velocity of downwash airflow decreased by 24.6% and 22%, respectively, from full load state to no-load state, which indicated that the intensity of the downwash airflow is reduced and can affect the penetration ability. The 100 μm droplets in position hysteresis state will decrease its velocity to 0 after transverse movement of 0.103 s and fall at a velocity of 0.307 m/s in the vertical direction, which will not significantly affect the spraying width. The newly designed VSS showed a 48% of pesticide usage reduction from conventional pesticide application, and this system also maintained the spraying uniformity throughout the total operational time.