Research On The Influence Law Of Wind Field On Plant Protection UAV Spray Drop Distribution

In recent years,plant protection drones have been increasingly used in agricultural production due to their high efficiency,wide operating range and low operating costs.The main factors affecting the spraying effect of the drone are the characteristics of the spray nozzle and the down washing field when the drone is in different flight states.However,due to the short development time of the drone spraying operation,there is limited previous plant protection experience.The research of the machine is mostly focused on the flight stability of the UAV,but the basic theory research on the spray drift of the UAV is lacking.Considering the rapid rise and extensive application of the CFD numerical simulation technology,this study adopts the numerical simulation technology.Combined with wind tunnel test and field test,the particle size and drift distance of fan-shaped nozzle and centrifugal nozzle at different horizontal wind speeds,as well as the under-washing flow and spraying effect of the drone during flight were simulated and tested.The findings and conclusions are as follows:（1）Numerical simulation of particle size characteristics and drift characteristics of two commonly used spray nozzles.The commercial computational fluid dynamics software Fluent was used to simulate the two nozzles spraying at different horizontal wind speed conditions.The two spraying conditions were:the fan nozzle Lechler LU 120-03 with spray pressure was 0.3 MPa,and the xaircraft 2018 centrifugal nozzle with the flow rate is0.6L/min,the rotation speed is 12000rpm,and then the data is analyzed by the scientific statistical software SPSS.The results show that for the pressure nozzle,the number median diameter of the droplets increases with the increase of the horizontal wind speed.Wind speed have significant effects for the spray nozzle drift characteristic values of both the test nozzles:for the fan-shaped nozzles,the time for the droplets to escape the 2m accurate deposition area under the influence of the horizontal wind speed is gradually reduced from 2s at 1m/s to 0.37s at 6m/s.The accurate deposition rate Ra decreases exponentially from 14.11%to 0.66%,and the horizontal drift rate R_h increases linearly from 14.25%to 60.58%.For centrifugal nozzles,the time during which the droplets escape the 2m accurate deposition area under the influence of horizontal wind speed 2s at1m/s is gradually reduced to 0.5s at 6m/s.（2）Two common models of spray nozzles spray droplet size characteristics and drift characteristics wind tunnel test.In the agricultural aviation wind tunnel of South China Agricultural University,the two spray nozzles under different horizontal wind speed conditions were tested and the results were statistically analyzed.The results showed that for the spray characteristics of the two nozzles,when the wind speed range from 0 to 6m/s,D_V0.1 decreases with the increase of wind speed,and the widths of D_V0.5,D_V0.9,v100 and droplets increase with the increase of wind speed;for particle size characteristics,In the vertical plane of behind nozzle 2 meters in the wind direction,when the wind speed is 1m/s,the spray deposition amount of both nozzles shows a downward trend,and when the horizontal wind speed is 3 and 6m/s,the deposition decrease with the height increase;in the case of the deposition’s relation with the drift direction,the deposition amount of the pressure nozzle is reduced with the increase of the drift distance,and the centrifugal nozzle is reduced according to the wind speed in wind speed is 1m/s,and is increased first and then decreased in wind speed is 3 and 6m/s.Comparing the wind tunnel test and numerical simulation results,it is found that there is a strong correlation between the two droplet deposition data,which proves that the numerical simulation results can reflect the test results.（3）X-shaped layout of the xaircraft P20 agricultural plant protection drone simulation.Select three representative wind field development stages after the start of the drone,that is,at the beginning of the drone start-up,the mid-term development of the wind field,and when the flight in stable,and show the wind speed profile contour and the swirling flow diagram of the rotor in the planes of front and left.Explore the conditions under different forward speeds.the absolute value distribution of the wind field velocity and the streamline diagram of the wind space around the fuselage.Further,by adding a discrete phase at the corresponding position of the nozzle,the airborne motion and the ground deposition are analyzed after the droplets leave the nozzle,it is proved that both the particles size of the discrete phase droplets and the laws of motion have changed significantly with the influence of the rotor under washing field.Relative to small particle size droplets,large particle size droplets are less likely to be affected by the lower wash wind speed and relatively more distributed around the periphery.When the drone hovers,the deposition concentration of the ground discrete phase is diffused and reduced from the bottom of the fuselage to the surrounding area.The sediment concentration is roughly symmetrical about the drone’s body,but the sediment concentration on the right rear of the fuselage will be too small.There is a region with a zero deposition concentration near the bottom of the fuselage.As the forward speed of the aircraft increases,the deposition area gradually moves back to the fuselage.（4）The xaircraft P20 agricultural plant protection drone field test.It is proved that the flight speed has an influence on the spray droplet deposition distribution.As the advancement speed increases,the average droplet size characteristic values DV0.1,DV0.5,and DV0.9 obtained on each collection belt tend to decrease.For each speed,the characteristic value of the droplet size of the deposited droplets fluctuates around a certain fixed value,and the particle size characteristic value fluctuates smoothly within the range of about 3 m on both sides of the spraying route.For the deposition data,the deposition droplet density and droplet deposition rate data are roughly symmetrical about the flight axis,with a wave-like drop from the center to both ends.Through the method of determining the width of the deposition of the droplet density determination method and the50%effective deposition amount determination method,the spray width of the P20 plant protection drone is obtained.It is proved that the effective deposition width data on the left side is larger than the right side,consistent with the simulation results.By comparing the manufacturer’s product brochure,it is found that the 50%effective deposition amount determination method is more accurate.Determine the spray width.On the other hand,by calculating the sediment deposition data at three different wind speeds,it is found that the sedimentation coefficient variation coefficients of the three wind speeds are 85.1%,95.3%,and 103.8%,respectively,which proves that as the forward speed increases,the droplet deposition effect tends to not uniform.