| Under the background of the national strategy of pesticide and chemical fertilizer reduction,plant protection UAV has developed rapidly because of its high efficiency,safety and drug-saving operation advantages.However,from the perspective of spray quality,the quality of plant protection UAV still needs to be improved,especially when the droplet size of spray droplets of UAV is small,and the liquid is liable to drift.To solve this problem,an induction electrostatic nozzle was designed on the basis of the existing unmanned plant protection nozzle,in order to enhance the power charge of droplets,improve the uniformity of spray flow field and reduce the drift rate of droplets.The main tasks completed are as follows:(1)By analyzing the principle of electrostatic spray charging and atomization,the main factors affecting the charging efficiency of droplets are found: the length of the plate,the distance between the plate and the fog film,and the charging voltage.On this basis,a two-stage induction electrostatic nozzle is designed by using induction charging method.The charge-mass ratio,particle size distribution and deposition uniformity of droplets were tested with the electrostatic spray nozzle.(2)A test bench for measuring the charge to mass ratio of electrostatic spray was designed.By analyzing the theory of droplet charge attenuation,the main factors affecting droplet charge attenuation are obtained,and the orthogonal experiment of the factors affecting droplet charge-mass ratio is carried out.The experimental results show that when the electrostatic voltage reaches 12 kv,the charge-mass ratio of droplets reaches its peak value,and the maximum charge-mass ratio is 1.62 mc/kg.(3)In order to find the spatial distribution of droplet size after charging,the influence of electrostatic field on the atomization degree of droplet was analyzed.Particle size measurement system was used to measure the droplet size of electrostatic spray.Around the influence of spray flow rate,spray pressure and electrostatic voltage on droplet size,single factor test and multi factor orthogonal test were carried out respectively,and SPSS software was used to fit experimental data.The results show that the droplet charge ratio is positively correlated with the electrostatic voltage,and negatively correlated with spray height and spray flow.Nozzle flow is the most important factor affecting droplet size,followed by spray pressure and electrostaticvoltage.Under the action of electrostatic field,the droplet size tends to decrease with the increase of voltage.The most obvious area of droplet size reduction is 0-200 mm below the electrostatic nozzle.(4)In order to find the droplet deposition law under the wind field of UAV,the droplet deposition effect between electrostatic spray and conventional spray is compared.The rotor wind field of UAV is simulated by ANSYS Fluent software,and the airflow distribution law is obtained.With the help of the multi rotor UAV spray test rig,the spray and spray uniformity tests were carried out.The experimental results showed that the droplet deposition rate increased by 27.8%,the droplet deposition density increased by 21.1%,and the deposition coverage rate increased by 15.9% compared with the conventional aviation spray.This research proves that the designed aerostatic nozzle has good charging ability.In practical application,the electrostatic field improves the breakage degree of liquid film in the initial stage of formation,and plays an auxiliary role in refining fog droplets.In terms of deposition effect,electrostatic field can reduce the negative effect of rotor wind field on droplet deposition,and effectively improve the droplet deposition volume and deposition density. |
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