Stereo PIV study of multirotor UAV downwash and spray dispersion

Multirotor unpiloted aerial vehicles are increasingly used for agricultural spraying. Spray dispersion is complicated by the interaction of adjacent rotor flows. Stereo PIV was used to map the flow field of a multicopter in a wind tunnel, to determine the effect of adjacent rotors and horizontal velocity. Spray droplet trajectories were modelled as they passed through the measured air velocity field. Comparisons were made to measured spray deposition patterns. Nozzle position plays an important role in spray dispersion and loss to wind drift. Placing the nozzle in the fastest part of the downwash is recommended. Zones of upward air motion at the tips of front and side rotors can exacerbate wind drift, and cause spray to impinge on the multicopter body.