Optimization Design Of Spraying System Of Plant Protection UAV Based On CFD Theory And Research Of Droplet Motion

Load delivery of multi-rotor UAV is a common technology for spraying operations such as agricultural plant protection,forest fire fighting and rescue.At present,there are bottlenecks in the plant protection operation of multi-rotor UAV:the establishment of droplet deposition model and drift model,the lack of understanding of the variability of multi-rotor UAV system parameters and plant protection operation parameters,so there are too many assumptions in the modeling,and the obtained model is too idealistic and conceptual,with high uncertainty in the results,and the accuracy is difficult to meet the demand.In order to recognize the uncertainty of spray deposition model and drift model of multi-rotor UAV and achieve the goal of accurate spraying,this paper takes multi-rotor UAV for plant protection as the research object,systematically analyzes the dynamic operation behavior and real-time airborne test methods in complex environment,and reveals the influence of operation parameters of multi-rotor UAV on droplet deposition and drift.Based on the theory of computational fluid dynamics,the spraying system of multi-rotor plant protection UAV is optimized,and the airborne variable spraying controller is designed and developed.High-speed camera was taken to study the movement track of fog droplets in complex environment,the statistical analysis model of droplet deposition and drift was established,which improved the effective utilization rate of pesticides and laid the technical foundation for precision agricultural aviation.The following are the main research contents of this paper:1.Based on computational fluid dynamics（CFD）theory,the influence of operation parameters on droplet deposition and drift is simulated and analyzed.The discrete phase model is used to simulate the droplet movement.By controlling the ambient wind speed,spraying pressure and spraying height,the droplet drift trajectory is described and the droplet deposition concentration is calculated.The statistical model of droplet drift with different operating parameters is established by the least square method,and the relationship between drift amount and drift distance is determined.The simulation results show that the variable coefficients of the fog droplet drift model established by environmental wind speed Xw(m s^-1),spraying pressure Xp（MPa）and spraying height Xh（m）are all positive,indicating that the three factors are positively correlated with edge drift distance,center drift distance and overlap width.2.The integrated airborne sensor data acquisition system and PWM variable controller are designed and developed,which realizes online real-time acquisition of environmental information parameters and variable control.The effectiveness of airborne sensor data acquisition system and PWM variable controller is tested by droplet deposition experiment,and the system operation parameters are optimized.The experimental results show that the best spraying pressure of XR8001 and XR8002nozzles is 300KPa,and XR8002 nozzles have higher droplet deposition density and amount.Deposition is not significantly affected by flight speed,but negatively correlated with nozzle pressure.3.The influence mechanism of downwash airflow on droplet deposition and drift in tip flow field of multi-rotor unmanned wing is simulated and analyzed by CFD method.The working parameters of pitch angle and motor speed are obtained by field experiment.The influence of wind speed and flight inclination angle on droplet drift results is analyzed according to droplet drift rate.Two methods to reduce droplet drift are put forward,i.e.nozzle moving forward and inclination angle compensation.The experimental results show that the flight angle has a significant impact on the droplet drift during operation,and the droplet drift rate can be reduced by moving the nozzle forward.4.High-speed camera system was taken for test experiment of droplet deposition and drift distribution in three-dimensional space.The trajectory of droplet movement in complex environment is studied,and the statistical analysis model of droplet deposition and drift is established.Field experiment results show that droplet drift is affected by flight speed,flight pitch angle and flight altitude.The results of particle capture show that the droplets fall irregularly,but in a real-time oscillation state.