Analysis and experiment on the effect of washing flow field and soybean canopy on droplet deposition during drone hovering

• Breakthrough the problem of inaccurate simulation of the interaction between unmanned aerial vehicle downwash airflow, fog droplets, and soybean canopy layer. • A crop model for soybean pod setting period was established using static porosity similarity method. 3) Explored the complex motion process and trajectory of fog droplets in the coupled field under the action of rotor downwash flow field. • Explored the sedimentation and movement characteristics of fog droplets assisted by downwash airflow in soybean canopy. • Design a gantry crane type plant protection unmanned aerial vehicle test bench. At present, the research on the interaction between UAV rotor wind field and crop canopy is mainly based on practical experiments, and there are few studies on the interaction between wind field, droplet and plant canopy in hovering state. In order to enrich this part, this paper studied the deposition effect of droplets on the soybean canopy when the multi-rotor plant protection UAV hovered under different loads. A combination of numerical simulation and indoor experiments is used to analyze the distribution of washing flow fields at rotor speeds of 300rad/s, 400rad/s, and 500rad/s, as well as the motion of fog droplets in the presence of the drone's washing airflow and the soybean canopy. A soybean plant model is created based on the principle of porosity similarity, and CFD simulation is conducted to analyze wind field distribution under different rotational speeds. Using gas-liquid two-phase flow, the motion of droplets in the soybean canopy under wind droplet interaction is simulated. The results show that a rotor speed of 400 rad/s achieves better spray uniformity and deposition effect. Indoor tests reveal that at a rotor speed of 300 rad/s, the average droplet deposition is 86.91 with a standard deviation of 42.42 and a coefficient of variation of 48%. At a rotor speed of 400 rad/s, the average droplet deposition is 105.2 with a standard deviation of 38.91 and a coefficient of variation of 36.79%. At a rotor speed of 500 rad/s, the average droplet deposition is 98.98 with a standard deviation of 39.97 and a coefficient of variation of 40.32%. Overall, a rotor speed of 400 rad/s yields the best spray effect, confirming the authenticity of the simulation and providing useful parameters for further research on UAV plant protection spray.