Numerical Simulation and Experimental Study of Air-Assisted Sprayer of Orchard

China was the biggest country producing and consuming fruits. Plant protection was an important segment to guarantee fertility and good fruits harvest. To realize the target, plant protection equipment and spraying technology were indispensable tools. Recently, the advantages of air-assisted spraying had been recognized and accepted in the orchard plant protection field, such as atomizing droplet twice, reducing droplet drift, increasing pesticide deposition and adhesion performance, improving pesticide efficacy, reducing the pesticide waste and environment pollution and cutting down the cost. But the gap in this field still existed compared with developed countries.This research was supported by the national 863 plan project (2008AA100903). Taking 3WZ-700 model self-propelled orchard air-assisted sprayer as research object, numerical simulation of air-velocity of fan was accomplished using the Computational Fluid Dynamics (CFD) commercial software FLUENT. Distribution of air velocity field was obtained. The simulation result was validated by experiment. Meanwhile, abundant experiments had been done on air-assisted spraying experiment equipment to describe its performance.The main research contents and conclusions were as follows:(1) A numerical simulation was conducted for air-velocity of fan. A physical model was established using GAMBIT. Mathematic model was established and simulated using FLUENT based on standard k-εmodel under appropriate boundary condition. Results showed that outlet wind velocity had little effect on the distribution. In the inferior part, the deflector had a great effect on the air velocity direction, including changing horizontal direction velocity diversification, increasing vertical direction velocity. Consequently, the droplet deposition deposited on the ground was reduced. Meanwhile, in the upper side, the deflector had little effect on the air velocity direction. Because of bigger air velocity in vertical direction, the droplets were carried to the upper side of canopy and the spraying coverage was also increased. This air velocity direction was suitable for target characteristic and could realize the effective and directional droplets deposition.(2) The distribution of air velocity field was measured by wind meter to validate the simulation value. Results showed that the experiment value was consistent with the simulation value. The velocity distribution was similar under different outlet wind velocity. The maximum points of velocity were different on different vertical planes. This distribution was matched with the real fruit tree crown. More droplets were carried to the crown interior. Meanwhile, the drift rate was reduced and the effective availability of pesticide was improved.(3) Spraying pressure, outlet wind velocity and angle of the deflector were the important spray parameters. To investigate factors influencing spraying performances, droplet diameter distribution, nozzle discharge and spray distribution on vertical planes were measured on air-assisted spraying experiment equipment. Results showed that the spraying pressure had much effect on the droplet diameter. The larger spraying pressure was, the smaller droplet diameter was. The droplet diameter was definitely smaller in air-assisted spraying than one in single spraying. Along the spraying range of 1-4m, three outlet wind velocities were corresponding average droplet diameters. The nozzles were good uniformity and the difference was less than 5% under different spraying pressure. The outlet wind velocity had definitely effect on the droplets deposition in vertical plane. The droplets deposition was different in the vertical plane under different angles of deflector. The spray distribution curve was similar to the velocity distribution curve in the vertical plane, so spray quality could be improved.(4) The droplets deposition and distribution of apple tree crown was experimentally tested at different sprayer travel speeds under the air-assisted spraying. Results showed that the more sprayer travel speed, the less droplets deposition. The droplets deposition on the right side of leaves was always much more than one on the wrong side of leaves. The droplets deposition in the vertical sections of canopy near the sprayer was much more than one far away from the sprayer. With different sampling heights, the droplets deposition on the upside was more than one on the middle, and the droplets deposition on the middle was more than one on the lower. Linear regression analysis results showed that the correlativity was remarkable between the sprayer travel speed and the droplets deposition in the front of canopy. With the sampling heights of 1.2m, the droplets deposition was inversely proportional to the sprayer travel speed on the right side of leaves. In the other sides, the sprayer travel speed had little effect on the droplets deposition.