Numerical simulation of downwash airflow distribution inside tree canopies of an apple orchard from a multirotor unmanned aerial vehicle (UAV) sprayer

Abstract

• A CFD model for predicting downwash airflow inside tree canopies was developed using computational fluid dynamics. • The wireless simulation parameter measurement system (WSPM-System) was used to provide real input data of the rotor speed for numerical simulation. • Most of the simulated values agreed well with the measured values, and the R2 values obtained were 0.84 and 0.89. • The airflow velocity inside tree canopies was highly and synthetically influenced by five factors of load, operation height, canopy diameter, tree height, and canopy densities. The downwash airflow from an unmanned aerial vehicle (UAV) sprayer has an important effect on the deposition and penetration of droplets inside canopies. Although UAV sprayers have been widely adopted in commercial spray scenarios in China, the study of downwash airflow inside tree canopies is still lacking. In this study, a CFD model for predicting downwash airflow inside tree canopies was developed using computational fluid dynamics (CFD). The tree canopies were defined as the porous medium in the computational domain. The wireless simulation parameter measurement system (WSPM-System) was used to provide real input data of the rotor speed for numerical simulation. The developed CFD model was validated in two steps through the measurement experiments of the vertical downward velocity ( V VD ) of the downwash airflow with trees ( EXP-With-Tree ) and without trees ( EXP-Without-Tree ). For the validation of cases with trees and without trees, the R 2 values obtained were 0.84 and 0.89, respectively, which meant that most of the simulated values agreed well with the measured values. The validated CFD model was used to predict downwash airflow distribution inside tree canopies of typical cases with various application parameters (load, operation height), tree dimensions (canopy diameter, tree height), and canopy densities. The application results showed that the airflow velocity inside tree canopies was highly and synthetically influenced by five factors but could not be determined by any and only one of them. The developed CFD model will be beneficial to make a better understanding of the effect of application parameters and tree structures on the distribution of downwash airflow inside tree canopies and provide references for the UAV sprayers application in orchards.