Simulating the dynamics of spray droplets in the atmosphere using ballistic and random-walk models combined

This paper presents a simulation model based on earlier work that combines both ballistic and random-walk models to describe the three-dimensional dynamics of spray droplets released in a specified direction from ground-based appliances in various weather conditions. The velocity of spray droplets is considered as a weighted sum of their ballistic and random-walk velocities scaled by a factor (1 - beta) and beta, respectively, where beta is defined as the ratio of the sedimentation velocity and the relative velocity between the spray droplets and the ambient wind speed. The contribution of the random-walk model to the initial velocity is seen to be negligible at first, but increases progressively, though not proportionally, as beta increases. As soon as the spray droplets attain their sedimentation velocities, beta = 1, the random-walk velocity component predominates and beta plays no further part in the calculations. The predicted effects close to the sprayer of the drop size, wind velocity and direction, evaporation on the transport process have been evaluated and combined to provide an analysis of spray drift.