Experimental Study On The Motion Characteristics And Drift Law Of Spray Droplets From Plant Protection Drone

Plant protection drone application technology is known for its precision,efficiency,flexibility and energy conservation,which have been widely used in the field of plant protection.Compared with traditional plant protection application machinery,plant protection drones are geographically adaptable,efficient and inexpensive to operate.Compared with traditional plant protection machinery,plant protection drones are geographically adaptable,efficient and cost effective.The airflow of wind field under the rotor of plant protection drones can coerce the droplets to deposit rapidly into the crop canopy,thus the droplet coverage and application safety are significantly improved.With the rapid development of plant protection drone application technology,this technology has become an important tool in the control of pests and diseases in China’s agricultural fields.Although the plant protection drone application technology has relatively improved the efficiency of liquid application in the process of farmland application,the liquid droplets in the process of plant protection drone application can drift and cause serious pollution to the farmland environment under the influence of the vehicle’s own parameters and atmospheric conditions.In this paper,based on the three controllable factors of spraying pressure,spraying height and rotor speed,we conducted an experimental study on the spraying droplet movement speed and droplet drift law of multi-rotor plant protection UAV by drawing on the relevant literature and combining the experimental conditions at home and abroad.The main research contents are as follows:(1)The wind speed variation law in the wind field under each UAV height and rotor speed under the test conditions is obtained by comparing the simulation and test results,and the rotor speed with the least wind speed variation fluctuation in the wind field is selected to provide support for the subsequent test.In this paper,a liftable plant protection UAV test stand is built to simulate the hovering height of the UAV.The rotor speed of the UAV at three throttle gears is measured using a laser tachometer,an isometric sketch of the plant protection UAV is drawn,and the wind field and wind speed at various points in the wind field are simulated using Solidworks flow simulations at different UAV heights.The wind speed was measured by an anemometer in the wind field of the lower rotor of the plant protection drone,and the wind speed fluctuation in the wind field at the rotor speed of 1590r/min(each spray height of 2700 mm,3100mm and 3500mm)was the smallest and most stable.(2)To analyze the change of droplet velocity under different spray pressure of plant protection UAV nozzle.A high-speed camera and a tracer light source are set up,and the images of fog droplets under different spray pressures are acquired at the same height and at a rotor speed that generates a stable wind field.Matlab,Python and EDPIV are used for image enhancement,grayscale and adaptive pre-processing,and the droplet velocity between two adjacent frames is calculated based on the PIV(particle image velocimetry)method.The test results show that the variation of spray pressure has a great influence on the droplet distribution and droplet speed;the droplet speed increases gradually with the rise of spray pressure at the same height and rotor speed of the plant protection UAV,and the spraying effect is improved.When the spraying pressure varied from 0.2 to 0.4 MPa,the droplet velocity increased with the increase of spraying pressure,the smallest at 0.2 MPa and the largest at 0.4 MPa.The spray pressure was 0.2mpa,and the droplet distribution was the most dense;the spray pressure was 0.3mpa,and the droplet distribution was gradually dispersed;the spray pressure was 0.4mpa,and the droplet distribution was the most dispersed.(3)To summarize the droplet drift law and the best working parameters of UAV application under the test condition of hovering,and to provide basic reference value for UAV drift prevention and reduction.The drift rate was calculated by comparing the total mass of spray droplets and the total mass of collected droplets,and the effects of three factors on the drift rate were analyzed: the spray pressure of UAV,the spray height of UAV and the rotor speed of UAV.The test results showed that the droplet drift rate increased when the spray pressure increased at a certain rotor speed and spray height;the droplet drift rate increased and then decreased with the increase of rotor speed at a certain spray pressure and spray height.At a certain spray pressure and rotor speed,the droplet drift rate decreases with the increase of spray height.The drift rate was the smallest at the spray pressure of 0.2Mpa,rotor speed of 2230r/min and spray height of 2700 mm.