Wind tunnel study of the changes in drag and morphology of three fruit tree species during air-assisted spraying

Abstract

Currently, air-assisted spraying is the most widely used high-efficiency pesticide spraying method used for treating fruit trees. Airflow from fans transports droplets into the canopy through kinetic energy. However, it changes the shape of the canopy and affects the deposition of droplets in the canopy. In this paper, through wind tunnel experiments, the drag forces exerted on three fruit trees (pear, peach and camellia) with different morphological characteristics were tested under different windspeeds. Changes in frontal area, canopy edge displacement, and optical porosity were recorded to determine the response of the trees that had different reconfiguration capabilities to the airflow and investigate the influence of porosity on morphological changes. The relationship between the drag force and windspeed was fitted through a power function, and the mean Vogel exponent for the pear, peach and camellia trees were −0.43, −0.54, and −0.31, respectively. Experimental results showed that the Vogel number of the same species of tree decreased with increasing porosity, and the morphological response of the canopy to the airflow was affected by the Vogel exponent. Canopy porosity had a significant impact on the Vogel exponent and the morphological changes of the canopy decreasing Vogel exponent with increasing porosity.