Air Jet Velocities in and beyond Apple Trees from a Two-Fan Cross-Flow Sprayer

The penetration of a sprayer air jet into an apple tree canopy was measured. An air-assisted sprayer with two vertical, cross-flow fan units, moving past the tree (without spraying liquid) provided the air jet. Treatments included three fan positions (fans vertical [0/0], top fan inclined 20° [20/0], and top fan inclined 15° with bottom fan inclined 12° [15/12]), three travel speeds (4.8, 6.4, and 8 km/h), two fan speeds (18 and 24.5 r/s), and three canopy conditions (south to north [SNT], north to south [NST], and north to south without a tree [NSO]). Vertical air velocities profiles were measured with hot-film anemometers in the center of the tree row and in the drive lane beyond the tree row. Maximum measured velocity, velocity integrated over the time of the air velocity pulse, air power (velocity cubed), and integrated power over the velocity pulse were measured or computed. The passing air jet produced distinct velocity pulses at elevations of 0.6 (except for [15/12]), 1.2, and 1.8 m within the tree and at elevations 0.6 and 1.8 m in the center of the drive row beyond the tree. Only fan position [0/0] produced distinct velocity pulses at the 3.0 m elevation, and no treatment produced visible pulses at the 4.2 m elevation. Fan positions had great and significant influence on air velocities inside tree canopies. At the 1.8 m elevation in the tree center, converging air jets [15/12] produced the highest velocities, followed by the [20/0] treatment. The plane jet [0/0] produced the lowest velocities at this position. Fan position had little significant difference on air velocities at the 1.2 m elevation in the tree. Fan speed had great and significant influence on air velocities. Travel speed produced little difference among treatments when maximum velocities were considered; however, there were greater differences when integrated velocities were considered. For the canopy conditions, greater velocities were measured for the treatments without canopy; however, velocities for the SNT treatment were nearly as great. Velocities for NST treatments were significantly less. This illustrates the effect of velocity sensor position (local canopy differences) on measured velocities. In general, converging air jets, low travel speed, and high fan output power improved penetration velocity and power into the tree canopy.