Multi-objective Optimization Design For Air Duct Of Air-Assisted Boom Sprayer

The wildly used boom sprayer in conventional field today in China is suffering some problems, such as serious pesticide drift, poor droplet penetration through the canopy of crops, less deposition of the lower part of crops, poor uniformity distribution, and serious effect of droplet drift reduction influenced by natural wind. On the basis of many domestic and foreign research on the air-assisted spray technology, this paper promote to drift reduction and higher pesticide deposition in the perspective of optimum structure parameters of air duct, novel flow deflector and optimized operating parameters under multiple working conditions. The novel flow deflector air-assisted duct boom spraryer is develped with strong anti-drift performance, which validate in the indoor experment and field test. The main work has been completed as follows:1,The anti-drift mechanism of air-assisted boom sparyer is analysised firstly, and mainly dicussed from the droplet accelerative motion by the function of air flow, secondary atomization, twist to the crop and boost to droplet penetration, and etc.2,Using computational fluid dynamics (CFD) technology to simulate the internal and external flow field of duct consisting of three-dimensional modeling area. Prototype duct flow field simulation results are analyzed. The analysis showed that there are strong swirlings of flow field, narrow flow channel in the prototype duct, and then lead high velocity variation coefficient of the work flow field.3,To improve the original design flaws of air duct of air-assisted boom sprayer, a multi-objective optimization approach integrated relevance vector machines (RVM), multi-objective genetic algorithms (MOGA) and fuzzy system is presented for the optimal design problem. Firstly, the multi-objectives of the air duct are constructed so as to improve the capability of reduced spray drift and increased penetration. The computational fluid dynamics (CFD) analysis of air-flow generating duct are utilized for sampling scheme given by uniform design to collect the train dataset. Sequentially, RVM based meta-model as fitness function is combined with MOGA to obtain the Pareto optimal set. Finally, a fuzzy inference system is established as decision-making support to obtain the optimum preference solution. Therefore, the optimized air duct structure with the round solution analyzed by CFD shows the promising improvement on flow speed variation. And the modified physical prototype proofed feasibility and efficiency of this approach. Improved export of prototype testing proved that the average wind speed improvement over an increase of 15.4%, 0.5m at an average wind speed increased 25.6% over the original design.4,To improve the drawbacks of original designed air-assisted duct of boom sprayer: huge wind consumption, low efficiency, large Coefficient Variation (CV) of wind velocity, the three-dimensional flow field of interior duct and exterior free flow region is simulated by using computational fluid dynamics (CFD). Flow field analysis of the simulation results showed that: strong swirling and narrow flow channel in the flow field of prototype air-assisted duct, and result in large CV in exterior free flow field. In response to these shortcomings, two kinds of improvement designs are proposed: (1) decreasing the outlet size and outlets spacing greatly reduces the CV of wind velocity, but not fundamentally change the flow structure; (2) on the basis of above optimization, adding a flow deflector overcomes the strong swirling flow and narrow flow channel so as to changing the flow field structure reasonable. The final scheme meets the design requirement. Two kinds of optimized designs provide an optimized boom sprayer and a direction for further air-assisted spraying optimization. Simulation results show that the hole-type plate can significantly improve efficiency but at the outlet velocity of 0.5 m below the larger coefficient of variation; slotted plate can be slightly more efficient, more a large degree of variation of wind speed reduction at 0.5m coefficient. Increase the slot spoiler, the prototype test wind speed coefficient of variation of 5.5%, compared with no additional wind deflector reduces the coefficient of variation 52.6%.5,Many studies have shown that air assisted spray have effect on the droplet drift reduction. However, the strength of the natural air flow effects on spray drifting reduction. In the wind field operations, the optimum working parameters is very important for the sprayer to reduce power consumption and droplet drifting, and to improve the plant surface drug deposition. However, to further improve the utilization of pesticides, reducing pesticide application rate, for the effects of pesticide spray technology has not been sufficient attention. This paper uses computational fluid dynamics (CFD) technology to study the air-assisted boom sprayer under the influence of natural wind, the wind flow field of air duct and discrete droplets in the three-dimensional interactive coupling region has been simulated. The results showed that: Increasing outlet velocity of air duct can stress target droplet movement to increase the droplet deposition rate. When the natural wind speed increases, the need to increase the blowing air speed can achieve better anti-floating effect. Air-assisted spray droplet drift angle on the reduction of loss of no significant impact. In order to establish optimal spraying control parameters, the different nature of wind drift model is established, and multi-objective optimization methods is used for the optimization of operating parameters, further fuzzy decision support system model is built to verify the non-considered variable operating parameters of prototype to correct the optimization parameters.6,The optimal designed prototype of air-assisted boom sprayer with flow deflector is built, and its air-assisted anti-drift and conventional spray operating modes are compared in the indoor experiment and filed test. The wind speed uniformity of air-assisted screen, anti-drift performance and secondary atomization performance are evaluated. Experimental results show that the droplet density sparyed by air-assisted boom sprayer with flow deflector increases 29.5% compared with the conventional sprayer and the distribution coefficient of variation decreases 78.5%. In droplet penetration test, droplet density in the crop top increases 52.5%, 37.4% lower distribution coefficient of variation; In the middle of crops, the droplet density increases 18.72%, 15.05% lower distribution coefficient of variation; In the bottom of crops, droplet density increases 61.7%, 18.3% lower distribution coefficient of variation. In secondary atomization performance testing, DR value increased 13.115 %. In anti-float test, drift loss by up to 66.7172%.