| Spraying pesticides with drones has many advantages such as strong terrain adaptability,low operating costs,high operational efficiency and will not cause harm to the health of famers,Therefore,it has developed rapidly in China in recent years,and has a wide range of applications.The six-rotor UAV is widely used due to its simple structure,stable operation and easy handling.However,due to the special rotor structure,the drone will generate a powerful downwash airflow when hovering in the air,it will affect the movement track of the liquid droplets sprayed from the nozzle during the sedimentation process,which will cause the mist of the liquid to drift or cause uneven application.In view of the above problems,this paper takes the flow field distribution of the nozzle spray plane as the research focus.Through the theory of leaf prime-momentum and strip theory,the mechanism of the generation and change of the slip flow of the six-rotor UAV propeller is deeply studied.And obtained the calculation model of the axial induced velocity of the slipstream generated by the propeller along the radial direction of the propeller,the characteristics of the non-uniform distribution of the jet flow velocity in the radial direction are obtained by calculation.On this basis,the whole lower airflow field of the six-rotor UAV was simulated by CFD simulation software,and the spray plane of each nozzle position in the flow field was analyzed.The law of airflow movement in the spray plane is obtained,and the reasonable installation position of the nozzle is proposed.and according to the slip flow velocity distribution,the nozzle layout scheme is proposed.A six-rotor UAV spray simulation test bench was designed to test the slip flow velocity distribution.The theoretical calculation results and simulation results were verified.The test bench was used to carry out the spray test under the propeller slip flow,and the influence of the airflow on the spray deposition effect when the nozzle was sprayed at different positions under the propeller was investigated.The results show that when the nozzle is sprayed directly under the propeller,the droplets drift the least,the total deposition amount is the highest,and the droplet deposition distribution is also minimally affected by the airflow.and Increasing the propeller speed at this location also helps to improve the uniformity of the deposition distribution of the droplets.Combined with the indoor spraying test results and the simulation results of the drone airflow field,seven different nozzle distribution schemes were proposed according to the flight mode of the drone,and the spray test was carried out outdoors.Finally,through the test results,it is concluded that for the six-rotor plant protection drone,when the X-type propeller structure is used for flight,the deposition effect is best when two nozzles are installed under the propeller on the rear side of the machine body and the propeller above the nozzle is externally rotated.In this way,the effective spray width is 2m,and the effective spray width average deposition density is95/cm2;When the I-type propeller structure is used for flight,the deposition effect is best when three nozzles are installed under the propeller on the rear side of the body.In this way,The effective spray width is 2.75m,and the average deposition density in the effective spray width is127.5/cm~2. |
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