| In recent years,China has made significant progress in the research and development of key components and technologies for UAV plant protection.But at present,there are still some urgent problems in the theory and technology of precision spraying based on the plant protection UAV.For one,there are relatively few studies on the mechanism underlying the influence of the rotor airflow distribution field of the plant protection UAV on the droplet spatial distribution and droplet velocity distribution.As a result,the effect of the rotor airflow distribution field of the plant protection UAV on the droplet spatial distribution and droplet velocity distribution is unknown.Further,it is impossible to fundamentally understand the mechanism of the influence of rotor airflow distribution field of the plant protection UAV on the droplet transportation process,droplet deposition and retention in the canopy of target crop.Secondly,the researchers mainly collected the droplet deposition data in the crop canopy through field tests to evaluate the application performance of the plant protection UAV,optimize the flight operating parameters of the plant protection UAV,and improve the application performance of the plant protection UAV.The labor cost,time cost,and economic cost required to conduct a field test are relatively high.At the same time,the time to conduct the field test is limited by the crop growth cycle.Which restricts the research progress of plant protection UAV spray technology to a certain extent.To address the above problems,in this paper,the DJI T30 plant protection UAV was selected as the application platform,and the combination of Computational Fluid Dynamics(CFD)and experiments method was used to deeply analyze the distribution and development characteristics of the rotor airflow distribution field of the plant protection UAV,explore the spray nozzle atomization characteristics,including,droplet size,velocity and spatial distribution characteristics,and clarify quantitatively the influence of rotor airflow distribution field of the plant protection UAV rotor on the droplet spatial distribution and velocity distribution characteristics.At the same time,The droplet retention model was built under the action of the rotor airflow distribution field of the plant protection UAV.And the droplet retention model is used as a tool to optimize the flight parameters of the plant protection UAV and improve the application performance of the plant protection UAV.The specific research work in this paper is as follows:(1)The T30 plant protection UAV was taken as the numerical simulation target.Based on the lattice Boltzmann method,the rotor airflow field of the T30 UAV was simulated to investigate the rotor airflow distribution and development characteristics,as well as the influence laws of rotor rotation speed,the coupling effect between rotor airflow,and the flight velocity and height of the UAV on the rotor airflow distribution and development characteristics of the plant protection UAV.The above study results lay a theoretical foundation for revealing the quantitative influence of the rotor airflow field of the plant protection UAV on the droplet spatial distribution and velocity distribution.Meanwhile,it provides theoretical guidance for the selection of plant protection UAV flight parameters.(2)The experimental study on the droplet size distribution characteristics was conducted to clarify the influence of nozzle type,spray pressure,and surfactant on the droplet size distribution characteristics and screen and optimize the nozzle-spray pressure-surfactant combination.The above work could improve the application performance of the plant protection UAV as well as provide the data basis for building the droplet retention model under the action of the rotor airflow field of the plant protection UAV.(3)The experimental study on the droplet spatial distribution and velocity distribution characteristics was conducted to investigate the influence of nozzle type,nozzle position,spray pressure,and rotor rotation speed on the droplet spatial distribution and velocity distribution characteristics,reveal the quantitative influence of the rotor airflow field of the plant protection UAV on the droplet spatial distribution and velocity distribution characteristics,and provide theoretical guidance for selecting the nozzle,spray pressure,and nozzle position when the plant protection UAV is used to spray.Meanwhile,the above work provided the data basis for the construction of the droplet retention model under the action of the rotor airflow field of the plant protection UAV.(4)The effects of the surfactant on the wetting and spreading ability of droplets on the rice leaves’ surface,the droplet deposition and penetration rate in the canopy of rice,and the droplet retention on rice plants were analyzed.The mapping relationship between the wetting and spreading ability of droplets on rice leaf surfaces and the droplet retention on the rice plants was revealed.Which provided a data basis for building the droplet retention model under the effect of the rotor airflow field of the plant protection UAV and evaluating the accuracy of the droplet retention model.(5)Based on droplet size distribution,droplet velocity,and the contact angle of the droplet on rice leaves,and combining the droplet interception model and the droplet impact model,a droplet retention model is built under the action of the rotor airflow field of the plant protection UAV.The accuracy of the droplet retention model was evaluated by comparing the droplet retentions on rice plants acquired by the model prediction and the field test(XR110-01VS).The error of the droplet retention model predicting the droplet retention on rice of water,1%Beidatong,1% Maifei,0.5% Maitu Target,and 0.2% Maitu 806 was 51.52%,18.26%,21.20%,14.42%,and 6.09%,respectively.The error of the droplet retention model in predicting the droplet retention on rice plants for the above four surfactants was relatively low.Which indicated that the droplet retention model could be used to predict the droplet retention of surfactant droplets sprayed by the plant protection UAV.Meanwhile,the droplet retention model was used to calculate the droplet retention on rice plants when TXVK-4 and IDK-120°-02 nozzles were selected to spray the above-mentioned five spray solutions with and without the rotor airflow field.The effects of the plant protection UAV rotor airflow field,nozzle type,and the surfactant on the droplet retention on rice plants were analyzed quantitatively.Which deepened the basic theoretical research of plant protection UAV spray technology and provided theoretical guidance for selecting spray nozzles and surfactants when the plant protection UAV is applied to spray in the field. |
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