Downwash airflow field distribution characteristics and their effect on the spray field distribution of the DJI T30 six-rotor plant protection UAV

• Published in: International journal of agricultural and biological engineering 2023-03, Vol.16 (2), p.10-22
• Main Authors: Zhang, Haiyan, Wen, Sheng, Chen, Chunling, Liu, Qi, Xu, Tongyu, Chen, Shengde, Lan, Yubin
• Format: Article
• Language: English
• Subjects: Accuracy; Aerodynamics; Air flow; Atomizing; Average velocity; Aviation; Computational fluid dynamics; Deposition; Downwash; Drift; Droplets; Fluid dynamics; Hydrodynamics; Nozzles; Particle image velocimetry; Plant protection; Rotors; Simulation; Spatial distribution; Spray characteristics; Spraying; Unmanned aerial vehicles; Velocity; Velocity distribution; Vorticity
• ISSN: 1934-6344; 1934-6352
• DOI: 10.25165/j.ijabe.20231602.8094

Spray characteristics are the fundamental factors that affect droplet transportation downward, deposition, and drift. The downwash airflow field of the Unmanned Aviation Vehicle (UAV) primarily influences droplet deposition and drift by changing the spray characteristics. This study focused mainly on the effect of the downwash airflow field of the UAV and nozzle position on the droplet spatial distribution and velocity distribution, which are two factors of spray characteristics. To study the abovementioned characteristics, computational fluid dynamics based on the lattice Boltzmann method (LBM) was used to simulate the downwash airflow field of the DJI T30 six-rotor plant protection UAV at different rotor rotational speeds (1000-1800 r/min). A particle image velocimetry system (PIV) was utilized to record the spray field with the downwash airflow field at different rotational speeds of rotors (0-1800 r/min) or different nozzle positions (0, 0.20 m, 0.35 m, and 0.50 m from the motor). The simulation and experimental results showed that the rotor downwash airflow field exhibited the 'dispersion-shrinkage-redispersion' development rule. In the initial dispersion stage of rotor airflow, there were obvious high-vorticity and low-vorticity regions in the rotor downwash airflow field. Moreover, the low-vorticity region was primarily concentrated below the motor, and the high-vorticity region was mainly focused in the middle area of the rotors. Additionally, the Y-direction airflow velocity fluctuated at 0.4-1.2 m under the rotor. When the rotor airflow developed to 3.2 m below the rotor, the Y-direction airflow velocity showed a slight decrease. Above 3.2 m from the rotor, the Y-direction airflow velocity started to drastically decrease. Therefore, it is recommended that the DJI T30 plant protection UAV should not exceed 3.2 m in flight height during field spraying operations. The rotor downwash airflow field caused the nozzle atomization angle, droplet concentration, and spray field width to decrease while increasing the vortex scale in the spray field when the rotor system was activated. Moreover, the increase in rotor rotational speed promoted the abovementioned trend. When the nozzle was installed in various radial locations below the rotor, the droplet spatial distribution and velocity distribution were completely different. When the nozzle was installed directly below the motor, the droplet spatial distribution and velocity distribution were relatively sym