Theoretical Analysis And Experimental Study Of The Droplet Deposition In The Downwash Flow Field Of Rotor UAV

When the UAV carries on the plant protection work,the effective spray width and other deposition index are affected by the droplet movement rule in the settlement process.By analysing the stresses of the droplets in the settlement process,the droplet movement equations are obtained in this article.A numerical algorithm is set up to calculate the droplet velocity and displacement,and the main factor affecting the droplet deposition are got.The droplet deposition laws of the centrifugal nozzle and the conical nozzle are tested,and the droplet deposition index in the rotor flow field is analyzed based on the downwash flow field distribution of the UAVs,the single-rotor UAV is used in the high-rod crops plant protection,and the six-rotor UAV is chosen for the low-rod crops.The specific contents are as follows:(1)Through the force analysis of the droplet,the motion equations are established,and the solving methord for the motion equations is designed by using MATLAB.The iterative calculation of the droplet velocity and displacement is realized.The effects of droplet size,initial velocity and wind field on droplet deposition are studied by theoretical calculation.The results show that wind field is the major factor affecting the droplet deposition.(2)The spraying systems for the centrifugal nozzle and the conical nozzle are set up,and a deposition experimental platform is estblished to study the variations of deposition parameters.The droplet initial velocities of the centrifugal nozzle are calculated by measuring the rotating speed,and that of the cone nozzle is got from the spray pressure.The effective spray widths at different heights are calculated based on the droplet motion equations,and they are analyzed by comparing with the experimental data.The results are as follows: 1)The effective spray width of the centrifugal nozzle decreases with the increase of the rotation speed of the atomizing disk.When the nozzle is at full speed,the effective spray width reaches the maximum within 0.5meter height,then it will be maintained with the increase of the nozzle height.2)The effective spray width of the conical nozzle increases first and then keeps maintained with the increase of the nozzle height.3)The trends of theoretical analysis and experimental results of centrifugal nozzle and conical nozzle are the same,the experimental values are larger than the theoretical values due to the drift of droplets,and the errors increase with the increase of the nozzle height.(3)The distribution of the downwash flow fields of TY-800 single rotor UAV and Dajiang T20 six rotor UAV are got by simulating with solidworks flow simulation module,and the spray experiments of centrifugal nozzle and conical nozzle are carried out in the downwash flow fields,the variation rules of the effective spray width and other parameters are analyzed.The prediction model is established,and the values in the model are compared with the experimental results,the results are as follows: 1)In the downwash flow field of single rotor UAV,the relative error of the predicted value and experimental value for the centrifugal nozzle is 9.6%,and the relative error of the difference of the effective spray width is 3.8%.The relative error of the predicted value and experimental value for the conical nozzle is 7.7%,and the relative error of the difference of the effective spray width is 1.0%.2)In the downwash flow field of the six rotor UAV,the relative error of the predicted value and experimental value for the centrifugal nozzle is 9.1%,and the relative error of the difference of the effective spray width is 1.1%.The relative error of the predicted value and experimental value for the conical nozzle is 9.7%,and the relative error of the difference of the effective spray width is 4.2%.The results show that the model can accurately predict the droplet deposition distribution in laboratory experiments.(4)A single-rotor UAV is used to carry out the spray experiment in the corn field and sugarcane field,the variation of effective spray width and other deposition parameters are studied,the results are as follows: 1)With the increase of the flight height,the effective spray width increases first but then decreases.2)The droplet penetration decreases with the increase of the flight height,which indicates that when the downwash flow field of the UAV is lower,the droplet penetration will decrease.Under the same conditions,there is no significant difference in the droplet penetration in the crop canopy between the centrifugal nozzle and the conical nozzle,that is,the increase of the initial velocity of droplets will not improve the droplet penetration in the crop canopy,which is consistent with the theoretical analysis.(5)A six-rotor UAV is used to carry out the spray experiment in the rice field and soybean field,the variation laws of effective spray width and other deposition parameters with the variation of the operational parameters are studied.A prediction model is established based on the characteristics of the downwash flow field at edge of the effective spray width,and the model results are compared with the experimental results,the results are as follows: 1)When the flight velocity is at 4.5 m/s,the effective spray width increases with the flight height,and it increases first but then decreases when the flight velocity is larger than 5.0 m/s;2)In the rice plant protection,the predictive value of the increacement of the effective spray width is 0.522 m,and the experimental value is 0.5 m,the relative error is 4.4%.The results show that the model can provide theoretical guidance for the prediction of deposition parameters such as effective spray width of the UAV.