MEASUREMENT AND PREDICTION OF HELICOPTER SPRAY NOZZLE ATOMIZATION

Abstract

Most wind tunnel experiments pertaining to shielded spraying have been conducted under stationary conditions.In field experiments, the interest has always focused on the investigation of drift amount. No information about the effect ofa moving shield is available, not to mention the effect of travel speed and travel direction on drift reduction. In this study,by using the FLUENT computational fluid dynamics software package, a double foil shield was used to investigate the effectof a moving shield on drift reduction under different travel speeds and travel directions (upwind and downwind). Relatedinformation on conventional spraying without shields was included. In addition, the moving effect of mechanical andpneumatic shields in a threedimensional flow with only one droplet release nozzle was further compared. Results of this studyindicated that local relative velocity plays an important role in controlling the drift potential of a moving sprayer: the higherthe local relative velocity, the greater the drift potential. When the sprayer moves upwind, drift potential increases slightlywith increased travel speed. However, when the sprayer moves downwind, drift potential decreases inversely with increasedtravel speed, as long as travel speed is less than wind velocity. For the double foil shield, moving upwind produced less driftpotential than moving downwind. Simulation results of comparing threedimensional shields showed that the double foilshield provided a drift reduction of 60.6% and 29.3% over conventional spraying when traveling upwind and downwind,respectively, at a speed of 1.34 m s 1 . The moving pneumatic shield with the best operating setting provided excellent controlof drift reduction for both upwind and downwind traveling at a speed of 1.34 m s 1 .