In recent years, extensive research has been conducted on pesticide application technology using unmanned aerial spraying systems (UASS) due to their efficiency and ability to overcome terrain obstacles. However, the coupling effect between the operational parameters of UASS and their influence on droplet deposition has not been sufficiently studied. A thorough and methodical analysis is essential to assess the deposition performance and drift risk of UASS. This study evaluated the spraying performance of an electric six-rotor UASS in wheat fields in Zibo between 2021 and 2022, focusing on three operational modes determined by flight speed and flow rate. Furthermore, the individual effects of these two parameters on droplet deposition quality and drift risk were explored. Based on the deposition quality of in-swath droplets and the drift degree after application, the results demonstrate that the optimal comprehensive characteristics of droplet deposition occur at a flight speed of 4.5 m/s, a flow rate of 2.025 L/min, and a spray amount of 1 L/ha. The increase in spray flow rate (2.475 L/min) results in a 3.92-fold enhancement in the deposition rate within the spray area compared with that of group of the minimum spray flow rate (1.575 L/min). A higher flight speed (5.5 m/s) improves the uniformity of droplet deposition, with the coefficient of variation decreases by 25.2% compared with that of the minimum flight speed (3.5 m/s), and this higher flight speed leads to a drift distance of 28.8 m.

Subsoiling is an important technology in conservation tillage. The disturbance characteristics of paddy soil were simulated by smoothed particle hydrodynamics (SPH) in this paper in order to explore the optimal tillage depth of paddy soil in a rice–wheat rotation area. Firstly, a subsoiling experiment with five tillage depths was carried out by a self-made multi-functional in situ test-rig facility. Then, a three-layer-soil subsoiling model of a cultivated layer, plow pan, and subsoil layer was established based on the SPH method. Finally, the soil disturbance characteristics were analyzed from macroscopic and microscopic perspectives. The results showed that the average draft force in simulation was consistently lower than in the field, with a maximum error of 18.71%, and the field draft force fluctuated greatly. The soil block above the tine was not lifted up as a big block but broken into many small soil blocks and then lifted up, resulting in different displacements of the soil particles, but the relative position was unchanged from top to bottom. The particle displacements were concentrated above the tine, the stress was concentrated around the tine, while the velocity and acceleration were closely attached to the subsoiler. A “mole cavity” at 25 and 30 cm tillage depths existed at the bottom of the disturbance, which was consistent with the finding in the field. The disturbance area and specific draft were maximum and minimum at 20 cm tillage depth, respectively. These findings suggest that the optimal tillage depth was 20 cm for the rice–wheat rotation area. The results of the analysis provide a theoretical basis for the optimal design of subsequent subsoiling.

The atomization performance of the nozzle is a critical factor influencing the pesticide application efficiency and drift behavior of agricultural unmanned aerial spraying systems (UASSs). However, the underlying atomization mechanisms of such nozzles have not yet been fully elucidated. In this study, a Particle Image Velocimetry (PIV) system was employed to evaluate the liquid sheet breakup mode, breakup length, droplet size distribution, and velocity distribution of a fan-shaped nozzle used in UASSs. Experiments were conducted under a series of spray pressures (ranging from 0.10 to 0.50 MPa, with an increment of 0.05 MPa) using sodium dodecylbenzenesulfonate (SDS) surfactant solutions at four concentrations (0%, 0.2%, 0.5%, and 1.0%). The results demonstrated that both the SDS surfactant and spray pressure significantly influenced the liquid sheet breakup process and atomization behavior. High concentrations of surfactant solution had a pronounced effect on the surface tension of the spraying liquid, delaying the onset of liquid sheet breakup, enlarging the overall droplet size distribution, and reducing the droplet velocity components along the X-axis and Y-axis. Conversely, higher spray pressures facilitated liquid sheet breakup, decreased the overall droplet size, and increased the droplet velocity distribution. This study provides fundamental experimental data for quantifying the effects of solution surface tension and spray pressure on the atomization performance of fan-shaped nozzles. These data provide systematic support for the evaluation of nozzle atomization performance.

To clarify the effects of rotor-induced downwash and crosswind on liquid sheet breakup and spray atomization characteristics of agricultural UAVs, an experimental platform integrating particle image velocimetry (PIV), a UAV spray system, and a wind tunnel was established. The droplet size and velocity characteristics of a flat-fan nozzle were investigated under different rotor speeds, crosswind conditions and spray pressures. The results showed that rotor-induced airflow significantly altered the post-breakup droplet characteristics. As the rotor speed increased from 0 to 2200 rpm, the volume median diameter (D_V0.5) increased from 206.45 to 245.06 μm (18.7%), while the volume fraction of droplets smaller than 150 μm (V_<150 (%_vol)) decreased from 12.86% to 10.26%, indicating a shift toward coarser droplets under stronger downwash. Crosswind exhibited a limited influence on the primary breakup process but substantially modified droplet transport. Without rotor operation, increasing crosswind velocity from 0 to 6 m/s reduced the mean horizontal droplet velocity by 77.0%, promoting lateral droplet displacement. Under rotor operation at 2000 rpm, the downwash effectively enhanced spray plume stability and mitigated crosswind-induced distortion. Furthermore, increasing spray pressure from 0.10 to 0.50 MPa reduced D_V0.5 from 274.29 to 222.24 μm and increased the proportion of fine droplets, demonstrating that spray pressure was the dominant factor controlling primary atomization. Overall, rotor-induced airflow primarily regulated droplet redistribution after atomization, whereas crosswind mainly affected droplet transport behavior. These findings provide theoretical guidance for optimizing UAV spray parameters and improving precision pesticide application efficiency.