【作者】 刘雪美；

【导师】 张晓辉；

【作者基本信息】 山东农业大学 ， 农业机械化工程， 2010， 博士

【摘要】 目前我国常用的大田喷杆喷雾机在施药过程中存在农药飘失严重,雾滴在冠层中的穿透性较差、作物中下部沉积少、分布均匀性差、雾滴减飘效果受自然风速影响较大等问题,在借鉴国内外对气流辅助式防飘喷雾技术的研究基础上,本文从风助风筒结构参数优化、设计安装新型结构导流器和优化多工况控制参数的角度,减少农药飘失,提高药物沉积率,研制了基于新型导流器的风助风筒型喷杆喷雾机,防飘效果显著,并进行了试验研究和性能测试。具体完成的研究工作如下:1、从理论上分析了气流辅助式喷杆喷雾机防止雾滴飘失的机理。2、采用计算流体力学(CFD)技术对风助风筒内流场及工作外流场组成的三维区域进行了建模和仿真。并对原型风筒流场仿真结果进行了分析,分析表明:原型风筒内流场存在强旋流、流道窄的缺点,导致工作外流场风速变异系数大。3、针对气流辅助式喷杆喷雾机的风助风筒原始设计的缺陷,提出了一种集成相关向量机、多目标遗传算法和模糊推理技术的多目标优化设计方法。首先为了增加辅助气流的减飘和穿透能力,构造出风助风筒的设计优化目标函数。利用均匀设计安排试验方案,并通过流体动力学仿真完成训练样本采集。选定相关向量机作为优化设计的评估函数。结合多目标遗传算法,求解出问题的Pareto最优解集,建立模糊推理系统获取问题的最终解。应用CFD验证经圆整后的最终解,其流速分布均匀性指标得到显著提高。改进的样机试验证明出口平均风速较改进前增加了25.26%,0.5m处平均风速较原始设计提高13.11%,0.5m处风速变异系数提高了35.6%。4、为彻底克服内流场强旋流、流道窄的不足,在结构参数多目标优化设计的基础上,增加导流器装置,更进一步优化了流场结构,减小损耗,提高效率,使流场在风筒长度方向上具有良好的风速一致性。本文还对两种不同结构的导流器对风筒的内流场和外流场的影响效果进行对比分析,仿真结果表明圆孔式导流器可大幅提高工作效率但出风口下方0.5米处风速变异系数较大;槽式导流器可小幅提高效率,更能很大程度的减小0.5m处风速变异系数。增加槽式导流器后,样机试验风速变异系数5.5%,相比未加导流器风速变异系数降低52.6%。5、在有风大田作业时,优化的喷雾机工作参数对于减小喷雾机功耗、减少雾滴漂移、提高植物表面的药物沉积非常重要。为进一步提高农药利用率、减少农药施用量,面向喷雾效果的施药技术应能得到足够重视。本文采用计算流体力学(CFD)技术,研究喷雾机在自然风影响下,风助风筒气流流场与离散雾滴在三维区域内的交互耦合作用,进行了综合仿真。结果表明:增大风筒气流出口速度,可以胁迫雾滴向靶标运动,增加雾滴沉积率。为了建立优化的喷雾机控制参数,建立了不同自然风速下减飘模型,运用多目标优化方法进行了工作参数的优化,并通过建立模糊决策支持系统对模型未考虑变量进行工作参数修正。6、对优化设计有导流器的气流辅助式喷杆喷雾机进行了样机设计和加工,并通过气流辅助喷雾和常规喷雾两种作业方式的室内试验、样机试验的对比,评价了有导流器的气流辅助式喷雾机的风幕风速均匀性、防飘性能和二次雾化性能。实验结果证明,有导流器的气流辅助式喷杆喷雾机与常规喷雾相比雾滴密度提高了29.5%,分布变异系数降低了78.5%。雾滴穿透性试验,在作物上层,雾滴密度提高52.5%,分布变异系数降低37.4%;在作物中层,雾滴密度提高18.72%,分布变异系数降低15.05%;在作物下层,雾滴密度提高61.7%,分布变异系数降低18.3%。二次雾化性能测试,DR值提高13.115%。在防飘测试中,飘失量减少达66.7172%。更多还原

【Abstract】 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%.更多还原