Study On Air-asssited Droplets Penetration In Dense Canopy Based On Stratification Porosity

High-density crop canopy has dense foliage,poor ventilation and light transmission,which is prone to diseases and pests.Air-assisted spray is a pesticide spray technology approved by plant protection industry.However,with respect to air-assisted spray for dense crop canopy,there is still droplets deposition attenuation in crop canopy with droplets interception of dense foliage,resulting in poor uniformity of droplet deposition and inferior control effect of pests and diseases.The distribution and deposition of spray droplets in crop canopy can be divided into two stages: the penetration and distribution of spray droplets in crop canopy and the attachment and deposition of droplets on local leaf surface.Uniform penetration and distribution of spray droplets is the prerequisite for their uniform attachment and deposition on leaf surface at different positions in crop canopy.The non-uniform penetration distribution of droplets is one of the important reasons for droplets deposition attenuation in dense crop canopy.In order to improve the uniformity of droplet penetration and distribution in dense canopy,it is necessary to clarify the penetration and distribution law of air-assisted droplets.However,the interaction mechanism between assisted airflow and crop canopy is not clear,and action pathways of assisted airflow for improving the penetration and distribution of spray droplets in crop canopy is unknown,resulting that the penetration and distribution law of air-assisted droplets in dense canopy is not clear.Therefore,it is of great theoretical and application significance to deeply analyze the interaction mechanism between assisted airflow and crop canopy,clarify the action pathways of assisted airflow for improving droplets penetration and distribution,and quantitatively reveal droplets penetration and distribution law stressed by assisted airflow in dense canopy.In this paper,cotton canopy in the middle and late growth stage is taken as a typical research object which has a dense canopy,and the research was carried out from the following five aspects:(1)Preliminary comparative study on action pathways of assisted airflow for improving spray droplets penetration and distribution in dense canopy was carried out.Starting from the analysis of influencing factors of droplets penetration and deposition in crop canopy,channel extension of droplets transport and enhancement of droplet transfer capacity were summarized as two pathways of assisted airflow for improving the uniformity of droplets penetration and distribution.According to comparative spray experiment results of cotton plants,it was preliminarily proved that enhancement of droplet transfer capacity was more helpful to increase droplets deposition on cotton canopy,and channel extension of droplets transport was more conducive to the improvement of droplet distribution uniformity.(2)The calculation model of static stratification porosity for cotton canopy based on morphological characteristics was established.Starting with the analysis of cotton morphological development characteristics and foliage spatial distribution features,it was found that foliage spatial distribution in cotton canopy has the statistical regularity.Then,the calculation model of stratification static porosity for cotton canopy was constructed,and the RMSE of the calculated static porosity of upper,middle and lower layers of cotton canopy at flowering stage were 3.97%,2.08% and 6.50% respectively,which realized the digital expression of foliage spatial distribution in cotton canopy,and quantitatively revealed the inhomogeneous characteristics of cotton canopy.(3)Modeling and experimental verification of flexible cotton leaf deformation under assisted airflow load based on fluid-structure coupling was carried.On the basis of measured mechanical parameters of cotton leaves,with the help of high-speed photograph technology,bidirectional fluid-structure coupling model of cotton leaf deformation under assisted airflow load was constructed and verified.Based on cotton leaf coupling model,orthogonal tests of cotton leaf deformation under assisted airflow load was carried out.Using the experimental data of cotton leaf deformation,mathematical model of cotton leaf deformation was established,and the RMSE of the calculated deflection of the petiole and main vein of leaf surface were5.13% and 10.43% respectively,which provides a basis for studying the interaction mechanism between assisted airflow and cotton canopy.(4)The calculation method of dynamic stratification porosity of cotton canopy considering leaf deformation under assisted airflow load was proposed.Based on the calculation model stratification static porosity,orthogonal tests of assisted airflow attenuation in cotton canopy were carried out.Furthermore,the mathematical model of assisted airflow attenuation in cotton canopy based on stratification static porosity was established,which clarified the overall attenuation trend of assisted airflow and the non-uniform distribution of assisted airflow in different regions of the same layer.On the basis of variation law of windward area of cotton leaves under assisted airflow load and the attenuation distribution law of assisted airflow in cotton canopy,calculation model of dynamic stratification porosity of cotton canopy was established,so as to quantitatively reveal the interaction mechanism between assisted airflow and cotton canopy.(5)Modeling and experimental verification of spray droplets penetration prediction in cotton canopy based on stratification porosity were carried out,and the mechanism of assisted airflow for improving spray droplets penetration in dense canopy was analyzed.On the basis of the above research,prediction models of droplet penetration and distribution in cotton canopy based on static stratification porosity and dynamic stratification porosity were constructed respectively.And these two models were verified through indoor spray test and field spray test.Based on the above two models,the mechanism of assisted airflow to improve droplets penetration and distribution in cotton canopy was revealed: channel extension for droplets transport is the main reason of droplets penetration ratio improvement in upper layer of cotton canopy,which is conducive to droplets smooth injection into cotton canopy and improve overall droplets deposition uniformity;enhancement of droplet transfer ability is the main reason of droplets penetration ratio improvement in middle and lower layers of cotton canopy,which is conducive to uniform distribution of spray droplets in middle and lower layers.