Submitted to: Transactions of the ASAE
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/21/2001
Publication Date: N/A
Citation: Interpretive Summary: Improved technology is needed to assure that spray applications of agrochemical and biological pest control agents are efficient in crop coverage with minimum losses to the environment. Among methods investigated to improve coverage and reduce drift loss is use of shields. While past wind-tunnel and field experiments with shields have shown promise, no definitive information on the all important airflow characteristics of moving shields have been secured due to the lack of research tools to do the difficult studies. In this work, computational fluid dynamic simulations were applied to analyze and compare the effects of a double-foil mechanical shield and a pneumatic (aerodynamic) shield with conventional, unshielded sprayer data. It was found that upwind or downwind sprayer travel speed play important roles in shield effectiveness in reducing drift loss. Upwind travel generally provided the better mitigation of spray drift. A moving pneumatic, air-curtain type of shield provided excellent drift reduction whether moving upwind or downwind. This research has provided a better understanding of basic shield characteristics and performance and will contribute to future implementation of shielded spray application technology.
Technical Abstract: Among methods investigated to improve coverage and reduce drift loss in agricultural spraying is use of shields. Most wind tunnel experiments with shielded spraying have been done under stationary conditions, while field experiments were always focused on drift. Thus, no data on moving shields are available as to travel speed and direction on drift reduction. Computational fluid dynamics (CFD), was used to study effects of moving double-foil and pneumatic shields on drift reduction for various travel speeds under upwind and downwind conditions. Also, effects of moving mechanical and pneumatic shields in three-dimensional flow with a single spray nozzle were compared. Results indicate that relative velocity has an important role in controlling drift from a moving shielded sprayer. The higher the relative velocity, the greater the drift potential. When a sprayer moves upwind, drift potential increases slightly with an increased travel speed. However, when the sprayer moves downwind, drift potential decreases inversely with an increased travel speed as long as travel speed is less than wind velocity. A double-foil shield moving upwind produced less drift than when moving downwind. Simulation results showed that a double-foil shield provided a drift reduction of 60.6% and 29.3% over conventional unshielded spraying when traveling upwind and downwind, respectively, at a speed of 1.34 m/s. A moving pneumatic shield under its best operating condition provided excellent drift reduction for both upwind and downwind travel at a speed of 1.34 m/s. These results provide better understanding of moving shield dynamics and will aid in developing better application systems.