| The movement of the droplet in the airflow field is gas-liquid-two-phase flow,and its characteristics of sedimentary drift are closely related to the characteristicparameters such as the gas flow field parameter,the droplet property,the relative position of the nozzle-target.At present,the law of the sedimentary drift of UAV(Unmanned Aerial Vehicle)droplets is mostly studied by field experiment and sampling method.However,the actual results are largely influenced by meteorological conditions and human factors.Moreover,the mostly used single factor method is difficult to comprehensively and deeply explore the law of the sedimentary drift of UAVdroplets and its influence mechanism.In order to improve the sedimentary efficiency of UAV droplets,this paper combined the method of multi-factor simulation with multi-parameter wind tunnel test to carry out the research on the law of the sedimentary drift of UAV droplets under the condition of variable spraying,which mainly focused on the following 3 parts:Firstly,CFD(Computational Fluid Dynamics)numerical simulation technique was used to research simulation of the law of the sedimentary drift of micro-UAV under multi-factors.Due to the large number of parameters affecting the law of the sedimentary drift of micro-UAV and large range of variableparameters,it was difficult to carry out the comprehensivewind tunnel test.However,the simulation test method can provide the basis for the actual wind tunnel test.In this paper,a three-dimensional gas field space of 8m×2m×2m simulating real wind tunnel was established.After setting the boundary conditions and simulation parameters,the law and amount of the sedimentary drift of micro-UAVdropletswas researched under different air velocity,spray height,droplet size,nozzle spray angle and other conditions.The result shows that the sedimentation drift of the droplet is distributed in the form of parabola below the nozzle,and the velocity of the airflow and the height of the spray have more significant effect on the sedimentation drift of droplet than droplet size and nozzle spray angle.Secondly,a variable spray measurement and control system based on pulse width modulation(PWM)technology was designed,and a flexible monitoring and control platform is developed.Thus,a basic platform for the research on the law of the sedimentary drift of micro-UAV droplets under variable spray was successfully developed.Liquid spray and the amount of sedimentationat unit time was important basis to evaluate the efficiency of spraying operation system.However,the downward flowgenerated by the high-speed rotation of the micro-UAV rotor had a significant impact on the sedimentary drift of droplets during UAV spraying liquid.In order to study the law of sedimentary drift of droplet under variable spray conditions,this paper designed a variable spray system based on micro-UAV platform,which includes multi-rotor micro-UAV,medicine box,micro diaphragm pump,centrifugal nozzle,PWM controller,remote communication module and so on to realize the remote control of spraying state and spraying parameters.Simultaneously,in order to carry out the research on the spraying law under different working conditions,flexible monitoring and control software platform based on virtual instrument technology and the idea of software reuse design was developed.Besides,test system platform was rapidly built and configuredthat can realized different spraying conditions.Thirdly,the experimental study on the atomization characteristics and thelaw of sedimentary drift of the micro-UAV droplets in the wind tunnel environment was carried outby using the developed variable spray measurement and control system.In order to realize the controllability of multi-parameters such as airflow field characteristics,droplet property and spray location during the test,the multi-rotor micro-UAV and variable spraying system are fixed in wind tunable wind tunnels.Thus,study on the law of sedimentary drift of droplets under controllable multi-wind speed can be realized.In the course of the experiment,the adjustment of the spraying amount of the liquid is realized by atomizing the turntable,and the atomization data of the actual spraying process is measured by the laser particle size analyzer.On the basis of the atomization test,the effect on the law of sedimentary drift of droplets under parameters including rotor wind field,flight height,airflow velocity,droplet size,spray angle etc.was studied,the variance analysis of all parameters was used to obtain the prediction model of the sedimentary driftof droplets.The results showed that the wind speed,flight height and droplet size are the most significant factors affecting the law of sedimentary drift of droplets.The rotor wind was a significant factor and the nozzle installation angle is not significant.The influence sequence of each factor on the law of sedimentary driftwas wind speed>flight Height>droplet size>rotor wind>nozzle installation angle.Based on the variable spray measurement and control system of micro-UAV developed in this paper,combined with the simulation results of multi-factor simulation,the droplet sedimentary drift law under the controllable parameters was studied in the wind tunnel environment.The result can provide operating condition of field spray of UAV(such as flight height control,buffer settings,environmental wind field resistance,etc.)spray parameters(such as spray angle,unit spray volume)and droplet settlement area prediction with technical support.In the field experiment,the influence of the natural wind field in the droplet deposition efficiency can be reduced after spray operating condition parameters was improved according to the wind tunnel test results,which has great significance to improve the utilization rate of the drug in the target area,ensure the agricultural production and reduce the environmental pollution. |
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