| Aeronautical pesticide application in plant protection has developed rapidly in recent years.It is favored for its high efficiency,good control effect,strong emergency response ability and water saving.Aerial spraying aircraft includes fixed-wing aircraft,single-rotor and multi-rotor helicopters.No matter what kind of plant protection aircraft,there is a certain degree of liquid drift,that is,when spraying pesticides,pesticide droplets or particles will deviate from the target or target area under the effect of environmental airflow and the flow field of the aircraft itself,causing pesticide damage to surrounding crops,waste of pesticides,environmental pollution and reducing the quality of pesticide application.This makes it difficult for the current plant protection aircraft to be widely used in herbicides and other types of pesticides,and also makes people have doubts about the new method of application,which limits its further promotion.Therefore,a suitable theory is developed to simulate the whole process of pesticide droplets from nozzle release to aerial movement to canopy contact.A life cycle model of pesticide droplets movement is established to accurately predict their trajectory,drift and diffusion,sedimentation and deposition.This model can improve aerial pesticide application technology,strengthen plant protection,food safety,environmental safety and ecological safety.All of them are of great significance.Firstly,the flow field of aircraft is analyzed.The lifting line equation is established,and the circulation distribution of the fixed wing aircraft is estimated by using the best m-Term approximation technique.The induced velocity at any point in the space around the body is calculated by Biot-Savart law,and the velocity law of the flow field of the monoplane is obtained.The N-vortex system is used to simulate the wake vortex formed by the nozzle.The intensity and position of the point vortex are determined by the Hamilton equation satisfied by the n-vortex,and then the induced flow field is obtained.Using momentum theory,blade element theory and streamline model,cylindrical tube model and stagnation point flow,the downwash flow field of single-rotor helicopter with different accuracy and complexity is obtained;Concentric circle model and cylinder model are proposed to estimate the flow field width of single rotor;An outline model of droplet interception is proposed to calculate spray amplitude;This paper puts forward the anti-drift theory of single-rotor helicopter,and establishes the drift control equation and flow control equation,which can make a flexible compromise among flight speed,altitude and flow operating parameters.Through theoretical analysis and literature comparison,the aerodynamic interference of multi-rotor aircraft is analyzed,and a simple isolated wake method is proposed.A semi-analytical vortex ring model is proposed to calculate the complete flow field of single rotor and multi-rotor.Secondly,the particle drift model is established.Based on the Lagrangian trace equation,the deformation Maxey-Riley equation is established through the force analysis of particles.By fitting the drag coefficient curve,the qualitative results of the equation are given and solved numerically.Then the drift control is implemented.The wave front is introduced and combined with the theory of atmospheric turbulence,the wave front trace equation is solved to control the longest distance of drift.The factors affecting the drift were treated as noise,and the feedback control was established to make the droplets settle to the canopy in the shortest time,and the application quality efficiency inequality was proposed.For thrush 510 G and other fixed wing aircraft,N3 and other single rotor helicopters,MG-1s and other multi-rotor helicopters,the drift model calculation and prediction are compared with the literature test,CFD and AGDISP results,with a total of 563 items.The validation shows that this model does not need spray amplitude input,and some AGDISP indicators are sensitive to this parameter.When the spray amplitude input is accurate,the drift prediction accuracy of agdisp exceeds that of this model.However,at present,agdisp cannot simulate micro single rotor or multi rotor UAVs alone,and must be linked with third-party flow field calculation software such as charm.For the fixed wing,the model in this paper has good robustness,and the predicted drift is more conservative than that of CFD and AGDISP.When the aircraft approaches the ground,the secondary vortices are considered in the model,and the predicted trajectory is more precise than that of agdisp.For a single rotor,the predicted performance of the model fluctuates greatly under different conditions.When the parameters are inaccurate,especially the information about the nozzle position and droplet size is lacking,the predicted value is quite different from the actual value.When the flight parameters have been optimized,the predicted results are in good agreement with the actual situation.For multiple rotors,the model performance is related to the rotor spacing.When the rotor spacing is large and the interaction is small,it can be treated as multiple single rotor deposition superposition.In addition,the prediction performance of multi rotor is more susceptible to natural wind,and the deposition curves may be greatly different under the same cross wind conditions.At present,the prediction accuracy of the model is the highest for the fixed wing,with a minimum correlation coefficient of 0.7083,an average correlation coefficient of 0.8115,followed by multiple rotors,with a minimum correlation coefficient of 0.1725,an average correlation coefficient of0.8190,and a single rotor,with a minimum correlation coefficient of 0.1409 and an average correlation coefficient of 0.7261.The results show that the model has the ability to predict the diffusion drift distance and ground sediment distribution for fixed wing,single rotor and multi-rotor,and can provide a reference for aviation spray practice. |
