| With the development of plant protection machinery and the maturity of air-blast spray technology,more and more air-blast orchard sprayer products are used for the prevention and control of fruit tree diseases and insect pests,which are generally driven by self-propelled chassis or tractors,with high operating efficiency and atomization Good and penetrating characteristics,suitable for a variety of orchard application requirements,the application effect and good pest control effect.The traditional orchard air-blast sprayer air-blast spray system generally generates airflow through axial fans,simple deflectors and air ducts.Traditional air-blast spray systems are prone to appear due to vortex airflow and asymmetrical outlet of the air duct due to blade rotation,etc.Uneven and turbulent phenomena in the airflow field of the air outlet affect the performance of the sprayer's liquid deposition uniformity and spray amplitude.Based on the self-propelled crawler undercarriage,this paper designs and develops a wind-driven spray system composed of axial fans,axial guide vanes and air ducts,etc.The method of combining fluid mechanics numerical simulation and experiment carried out the design,numerical simulation and experimental verification research of air-blast spray system,which provided a reference for the development of scaffold orchard spray machinery.The main research contents of this article are as follows:(1)This paper summarizes the domestic and international status of orchard planting models and plant protection machinery,and expounds and analyzes the asymmetry of airflow and droplet deposition on both sides of the traditional sprayer.The different types of orchard air-blast sprayers at home and abroad were summarized and discussed.The asymmetric and uneven phenomena of airflow and droplet deposition on both sides of the existing traditional sprayer were analyzed,and the design ideas of the air-blast spray system in this paper were discussed.With technical routes.(2)Design and numerical model research of air spray system in scaffold orchard.According to the typical scaffolding pear orchard planting model in southern Jiangsu,the design and selection of air-blast spray system were carried out.According to the parameters of air-blast spray system and axial fan,the corresponding axial guide vane,air duct and deflector structure were designed.The grid-independence of the airflow field numerical model of the air-blast spray system and the adaptability of the turbulence model were carried out.The airflow field analysis results of three different turbulence models of standard,RNG and SST were analyzed and compared.According to the evaluation indexes,the grid division scheme of the numerical model and the type of turbulence model are determined respectively.A numerical analysis and comparative study was carried out on three different duct structures with different outlet widths.Based on the air volume,the average airflow velocity and pressure loss of the outlet,the duct structures with different outlet widths were evaluated,and the duct width was determined to be 80 mm.(3)Numerical analysis and experimental verification study of the airflow field of the air-blast spray system.The numerical model of the airflow field of the wind speed sprayer was established,and the distribution characteristics of the internal and external airflow fields of the air-blast spray system were studied by numerical simulation.Analyzes the change of the velocity streamlines and pressure of the internal and external airflow field when the airflow passes through the fan blades,guide vanes and air ducts.The experimental verification study of the prototype of the air-blast spray system was carried out,and the airflow velocity at the outlet of the air duct and the external airflow field was measured at multiple points using a three-dimensional ultrasonic anemometer and other methods.The analysis compares the airflow velocity distribution on both sides of the air duct.The results show that the air flow at the right outlet of the air duct changes greatly,the air flow at the left side changes gently,and the air flow at both sides of the external air flow field is symmetrical near the air duct.In addition,the analysis results show that the relative error between the simulated value of the airflow velocity at the outlet of the air duct and the test value is basically 10%-20%,and the simulated value of the airflow velocity at 0.5m and 1m from the outlet of the air duct is in good agreement with the test measurement value.The speed difference between the two is 1-2m/s,but there is a large deviation between the simulated value of the velocity and the measured value at a higher and further distance in the external airflow field.The measured value of the airflow velocity is 2-3 times the simulated value.(4)Numerical analysis of gas-liquid two-phase flow field and verification of droplet deposition test in air-driven spray system.The particle size distribution and deposition distribution of the droplets on both sides of the sprayer under the operating pressure of 1MPa and 2MPa were studied using numerical simulation and experimental verification methods.The test results show that at 1 MPa and 2 MPa spray pressure,the difference in the amount of droplet deposition on both sides of the sprayer does not change much,and most of the droplet deposition is distributed within the range of 0-1.8m.The height of the fruit trees is consistent.Through the verification of the simulation results,it can be seen that under the spray pressure of 1 MPa and 2 MPa,the simulated value of the droplet deposition amount(percentage)on both sides of the air duct is basically consistent with the experimental value in the height range of 0.3m-1.8m,and the relative error of the simulation is 20 %the following.The simulation results for the deposition of fog droplets at lower locations are lower than the test values,with a relative error of 30%-40%,while the results for the deposition of fog droplets at high locations are higher than the test values,and the relative error with the test values is More than 60%. |
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