A Virtual Nozzle for Simulation of Spray Generation and Droplet Transport

Abstract

The objective of this study was to develop a computer simulation model that mimics the collective behaviour of droplets in the spray cloud from a flat-fan hydraulic nozzle. The break-up region of this virtual nozzle was discretised into a mesh that ejected the droplets in radial directions . The initial size and corresponding velocity of each droplet ejected was selected at random from a two-column array of data for more than 10 000 actual droplets. That composite data file was collected from three different test nozzles of the same type and size (Spraying Systems TeeJet ® XR8002 nozzle operating at 207 kPa with tap water) with a phase/Doppler particle analyser (PDPA) traversing a plane 4 cm below the tip of each nozzle. The transport model employed an effective drag coefficient that accounted for aerodynamic drag , air entrainment and mutual interference of droplets in addition to effects of evaporation and vertical wind velocity fluctuations . Simulated targets collected the droplets at points 45 cm below the virtual nozzle to study deposition patterns. The virtual nozzle was calibrated to produce the same volumetric pattern and discharge rate as that of the test nozzles. The simulated deposition pattern from the calibrated virtual nozzle was very similar to the droplet size and number distribution measured with the PDPA 45 cm below the test nozzles. The measured and simulated mean and median diameters were of a good match.