Numerical simulation of spray drift and deposition from a crop spraying aircraft using a CFD approach

Spray drift from aerial application is a great concern and there have been many efforts to predict it. Here computational fluid dynamics (CFD) techniques are used to predict the velocity field and the subsequent trajectories of spray droplets in the wake of a Thrush 510G aircraft. The fluid phase is modelled using the Reynolds-averaged Navier-Stokes (RANS) equations within an Eulerian frame, whilst the dispersed phase is modelled using a stochastic tracking model in the Lagrangian frame. The wake of aircraft is represented with a pair of wing-tip vortices and droplets are released in ten locations representing atomisers mounted below the wing. Firstly, a case without the presence of crosswind was simulated and deposition analysis was performed. A case with the presence of crosswind was then simulated to predict spray drift and deposition. The locations droplets at different times, as well as evaporation rate, were compared with AGDISP (agricultural dispersal model) predictions. The physics of vortices evolution, droplets motion and evaporation were analysed to explain the drift and deposition characteristics.