气流雾滴胁迫和冠层孔隙变化对沉积性能影响解耦研究

Decoupling on Influence of Air Droplets Stress and Canopy Porosity Change on Deposition Performance in Air-assisted Spray

气流辅助喷雾中气流导致的冠层孔隙变化和对雾滴胁迫作用的影响是耦合的,两者最终影响雾滴沉积性能,明晰两者的耦合比例对沉积性能的影响,可为风送参数优化和喷雾模式改进提供指导。本文以盛花期棉花为研究对象,通过设计解耦试验方案,分析气流辅助施药过程中气流雾滴胁迫和冠层孔隙变化对雾滴沉积行为的不同影响。首先,借助高速相机标定棉花枝叶风载下的变形量,得到气流速度、叶面积、变形量三者间的拟合关系,通过仿真叶片风载变形试验得出,仿真叶片与真实叶片的风载变形相对误差在17%之内,从而确定了仿真枝叶模型应用于风送喷雾试验的可行性;然后,基于棉花生长发育的枝叶构型3/8规律,搭建冠层孔隙可风载变形的方案1棉花模型,测量方案1棉花冠层内气流场数据,计算风载后枝叶变形量,并使用物理手段固定枝叶变形量,形成风载变形后冠层孔隙固定的方案2棉花模型,将自然状态下棉花枝叶固定,保持风载下冠层孔隙不变作为方案3棉花模型;最后,针对3种试验方案的棉花模型,通过改变辅助气流风速进行了风送沉积试验。结果表明:相较于冠层孔隙变化,气流对雾滴的胁迫作用更有利于雾滴在冠层内的沉积行为,两者对于雾滴沉积量的提升比例分别为39.81%和10.52%;相比于气流对雾滴的胁迫作用,冠层孔隙增大形成的雾滴运移通道更有利于雾滴在冠层内的均匀分布,两者对沉积均匀性的提升比例分别为42.71%和1.10%。本研究可为基于不同作物冠层孔隙变化特性的新型喷雾模式设计提供参考。

In the air-assisted spray,the change in the porosity of the canopy caused by the wind speed of the auxiliary airflow and the effect on the droplet migration were coupled,and the two ultimately affected the droplet deposition performance.Studying the effect of the coupling ratio of the two on the deposition performance can provide guidance for the optimization of air-assisted spray parameters and the improvement of spray patterns.Taking cotton in the full blooming period as the research object,and the different effects of the decoupling of the two on the droplet deposition behavior were analyzed by designing a decoupling test plan.Firstly,the deformation of cotton branches and leaves under wind load was calibrated with the help of a high-speed camera,and the fitting relationship among air velocity,leaf area and deformation was obtained.Through carrying out the wind load deformation test of the fake blade,it was verified that the wind load deformation error of the fake blade and the real blade was basically less than 17%.The plan of using the simulated cotton model to be applied to the air-assisted spray test was determined.Then,according to the 3/8 rule of the branch and leaf configuration of cotton growth and development,a cotton model of Scheme 1 in which the canopy porosity can be changed by wind load was built.The data of the airflow field in the cotton canopy was measured,and the deformation of branches and leaves under different wind speeds was calculated.Physical means were used to fix the deformation of branches and leaves,and a Scheme 2 cotton model was formed with fixed canopy porosity after wind load deformation.The cotton branches and leaves was fixed in the natural state and the canopy porosity was kept unchanged under wind load as the cotton model of Scheme 3.Finally,for the cotton models of the three test schemes,the auxiliary air flow velocity was changed to carry out air-assisted droplet deposition experiments.The test results showed that the migration effect of airflow on droplets was more favorable to the deposition behavior of droplets in the canopy than changes in canopy porosity.The effect of air flow on the movement of droplets increased the droplet deposition rate by 39.81%,and the change in canopy porosity increased the droplet deposition rate by 10.52%.The droplet transport channel formed by the increase of canopy pores was more conducive to the uniform distribution of droplets in the canopy than the transport effect of airflow on the droplets.The increase in the porosity of the canopy increased the deposition uniformity by 42.71%,and the transport effect of the air flow on the droplets increased the deposition uniformity by 1.10%.This decoupling method can provide a reference for the design of spray patterns for different crop canopy porosity changes.