The Downwash Aggregation Of Four-rotor And The Effect On Spray Deposition Characteristics

In order to improve the droplet deposition efficiency of multi-rotor plant protection drones,this paper uses the numerical simulation method to carry out the research on the droplet deposition characteristics of the four-rotor UAV,which is mainly reflected in the following three aspects:(1)Explain the mechanism of the polymerization effect of the four-rotor under-washing gas flow and the evaluation method of spray deposition quality.According to the formation process of the lower airflow of the rotor,the variation of the wheelbase of the four rotors on the distribution of the near-ground vortex in the rotor gap,the near-ground vortices interfere with each other to affect the degree of polymerization between the lower jets of the rotor,and the lower purge flow The gas flow rate increase rate η and the gas flow polymerization degree under the polymerization effect are defined.(2)Exploring the effect of the variation of the four-rotor wheelbase on the polymerization effect of the lower wash gas stream.A four-rotor UAV wind field spray model was established,and the dimensionless parameter aspect ratio was defined as the ratio of the rotor wheelbase to its diameter.The calculation of the flow field of the four-rotor under the diameter-to-diameter ratio of 1.1~2.0 is carried out,and the polymerization flow law between the wheelbase change and the four-rotor downwash flow is explored.The influence of the forward speed of the four-rotor on the polymerization phenomenon of the lower wash gas flow is analyzed..The results show that when the rotor-to-diameter ratio is in the range of 1.1 to 1.4,the higher the rotor-to-diameter ratio,the lower the degree of polymerization.As the forward flying speed increases,the degree of polymerization of the lower washing gas increases,and the optimum polymerization position increases.(3)The effect of the polymerization effect of the four-rotor under-washing gas flow on the droplet deposition characteristics was investigated.A discrete phase droplet was introduced to simulate the spray flow of the four-rotor under-wash flow field.In order to explore the influence of the polymerization effect of the lower wash gas stream on the droplet deposition characteristics under different working conditions,the distribution of droplet deposition and the change of particle size distribution in each spray field were analyzed under different forward flight speeds and nozzle distribution modes.The results show that the effect of the airflow polymerization under the rotor has a positive effect on improving the anti-drift ability of the droplet group.When the no-washing gas polymerization effect occurs,the four-point distribution of the nozzle is more conducive to the deposition of droplets of 0~100μm and 100~200μm particle size,and the spraying effect is better.