Spray Model Of Single Rotor Unmanned Plant Protection Machine And Its Application In Tropical Crops

In recent years,the plant protection UAV（Unmanned Aerial Vehicle）have achieved unprecedented development in China,among which the single-rotor UAV has a stable wind field,and the downwash wind field helps to improve the penetration of droplets deposition and spray them onto the back of the leaves,so the single-rotor UAV market occupies a very important position,and the3WQF120-12 single-rotor UAV is one of its typical representatives.At present,3WQF120-12 single-rotor UAV has some practical experience in low crops,and some better operating parameters have been screened out,but there are still no detailed in-depth study on its spraying theory,the droplet spray droplet distribution spectrum distribution of the nozzles,the rotor wind field distribution,the droplets are affected by the wind field,the concentration of the droplets deposition and the change of regional laws still need to be further in-depth study.In this paper,the effects of UAV nozzle models Lu120-015 and Lu120-02,rotor structure and wind field distribution,spray pattern of spray droplets,operating parameters and environmental parameters on the laws of spray droplet movement are tested and simulated.The research and CFD（Computational Fluid Dynamics）simulation results were verified by field and wind tunnel tests.The main research contents and records are as follows:（1）Spray nozzle type,spray pressure,installation location and number are the key factors of spray system.In the indoor and wind tunnel,two types of nozzles,Lu120-015 and Lu120-02,were measured by laser particle size analyzers under different spray pressures and wind speeds.The results showed that:The width of the droplet size spectrum becomes larger as the wind speed increases;The particle size distribution uniformity of drops becomes worse,the droplet spectrum width ranges from1.02 to 1.49,The droplet size has an exponential relationship with the wind speed,and the degree of fitting is high;As the spray pressure increases,the droplet size decreases;When the spray pressure of Lu120-02 nozzle increased,the values of Dv_0.5 and Dv_0.9 decreased and there was a significant difference from the small spray pressure（P<0.05）;When the spraying flow rate is similar,the droplet diameter of the large-aperture nozzle was larger;There was a significant difference in droplet deposition drift between wind speeds of 1 m/s and 6 m/s（P<0.05）;The furthest and closest drift distances were 12.77 m and 6.27 m,respectively.（2）Quantitative results can be obtained by changing the controllable factors in the wind tunnel to test the spray nozzle spray characteristics.Combined with the results of wind tunnel tests,CFD（Computational Fluid Dynamics）software Ansys Fluent was used to model the two types of nozzles.A computational domain model of exactly the same size as the wind tunnel was established in Fluent.Comparative analysis of extraction spraying simulation value and test value,the Pearson correlation coefficient between each group of data showed a very strong correlation,up to 0.99283,it proves that the CFD simulation results were feasible.In Fluent,the particle duration and particle distribution distribution of different particle sizes in the domain can be calculated statistically.It can more intuitively express the movement law of the entire droplets,and the display details were more abundant.In the calculation domain,the cloud concentration maps of the droplet deposition concentration in the vertical and horizontal sampling planes were modeled after the wind tunnel.It was observed that the droplet deposition area on the horizontal plane gradually changed from an oval to a dovetail shape,and then gradually merged and narrowed down.The cloud concentration map of droplet deposition in the vertical plane shows that the deposition area becomes larger at higher wind speeds.The highest height is about 0.47 m.（3）The distribution of rotor wind field,flight speed,altitude and environmental crosswind of single-rotor UAV directly affect the trajectory of drops.In this paper,the model of 3WQF120-12 UAV was built in the Pro/Engineer software.Both the main and the tail rotor were modeled in reverse using3D scanning using Geomagic Design X software.In the Ansys Fluent,the outflow field calculation domain,main rotor rotation domain,tail rotor rotation domain and discrete phase were set up for calculation.A total of 16 groups of different front winds and cross winds from 0-0 to 6-6 were combined to observe the droplet deposition.The results show that:The spray model can simulate the droplet trajectories of 16 groups under the action of the combined wind field in a detailed and comprehensive manner,including:particle movement duration,particle size and distribution,wingtip vortices,cloud image of droplets deposition concentration at different heights,and droplet deposition regional deformation law,etc.;When the wind speed was greater than 3-3,the particle size of the droplets group was obviously stratified,The particle size of the droplets group was mainly 200～320μm,and the droplets<150μm,were rolled to the top of the UAV.When the spray height was less than 1 m,the droplets were concentrated and the deposition area was small,which was not conducive to the full diffusion of the droplets,resulting in excessive local droplet density;When the spray height was less than 1 m,droplets were concentrated and the deposition area was small,the droplets were too scattered,and the deposition was uneven,which was not conducive to accurately acting on the target;When the spraying height was more than 3 m,it was greatly affected by the environmental wind.The droplets were too dispersed and the deposition was not uniform,which was not conducive to the precise action on the target.The data of sampling lines at different heights show that under each treatment,H=1 m was significantly different from 3,6 and 10 m in droplet deposition concentration.The operation height of UAV should be carefully selected according to the simulation results and the actual situation.（4）The 3WQF120-12UAV has achieved some results in flight defense of crops such as wheat and rice.However,little research has been done on the test of tropical crops.In this paper,a field experiments were carried out on the tropical crop pineapple.The control factors were environmental wind speed and operating height,the droplet size distribution,droplet deposition and drifting law,penetrability and percent area coverage during the spraying test were studied.The results showed that:The operating height was below 2.5 m,the crosswind was below 2 m/s,the droplets deposition can reach 0.1227/（88）,the average area coverage was 2.26%,and the total drift can be as low as15.42%.The 90%drift distance of all treatments was 3.7 m～46.5 m;Operation height of 3.5 m and crosswind wind speed above 3.7 m/s had the worst spray quality,it should be avoided in the application;The field test results were compared with CFD simulation,and the simulation results were proved to be feasible.Combining CFD simulation results and field tests,it is recommended that pineapples be operated at a wind speed of 2 m/s and an altitude of 2.5 m or less when flying.And a drift area of more than 15 m showed be reserved in the operation.（5）In order to explore the application of this model in flight defense on high-stalk crops,field experiments were conducted on betel nut.The control parameter was UAV operating height,the deposition characteristics,penetrability,droplet drift and ground loss of betel nut canopy were studied.The results showed that:Ambient wind and operating height had a significant impact on the mean value of the droplet diameter.The diameter of the droplet was about 240μ8),which was more conducive to the penetration of the droplet to the trunk.When the operation height was low,the droplet deposition level at the top of the crop canopy and the largest diameter of the canopy was higher,up to 53.27%and 31.53%,and the level of droplet loss on the ground was 19.9%;When the UAV’s operating height were exceeds 10 m,the 90%of the spray droplets can up to 36.35 m,which should be paid enough attention.Due to the high operating altitude of betel nut during flight defense,combined with CFD simulation results,the accumulation of droplets at the boundary of the calculation domain can be observed at ambient wind speeds above 3 m/s,and the spray area has severely deviated from the course direction.In practice,attention should be paid to prevent the leakage of heavy spray and it is not recommended to operate under the ambient wind speed.Based on the 3WQF120-12 UAV in the wind tunnel test,field test and CFD simulation,It is proved that the spraying mechanism of the UAV spraying model in the paper was correct and feasible.It can provide theoretical and data support for field application and spray mechanism research of this model and other similar models.