title: Simulating droplet motion on virtual leaf surfaces.
abstract: A curvilinear thin film model is used to simulate the motion of droplets on a virtual leaf surface, with a view to better understand the retention of agricultural sprays on plants. The governing model, adapted from Roy et al. (2002 J. Fluid Mech. 454, 235-261 (doi:10.1017/S0022112001007133)) with the addition of a disjoining pressure term, describes the gravity- and curvature-driven flow of a small droplet on a complex substrate: a cotton leaf reconstructed from digitized scan data. Coalescence is the key mechanism behind spray coating of foliage, and our simulations demonstrate that various experimentally observed coalescence behaviours can be reproduced qualitatively. By varying the contact angle over the domain, we also demonstrate that the presence of a chemical defect can act as an obstacle to the droplet's path, causing break-up. In simulations on the virtual leaf, it is found that the movement of a typical spray size droplet is driven almost exclusively by substrate curvature gradients. It is not until droplet mass is sufficiently increased via coalescence that gravity becomes the dominating force.
authors.affiliation: Mathematical Sciences , Queensland University of Technology , Brisbane, Queensland 4001, Australia.
authors.forename: Lisa C
authors.initials: LC
authors.lastname: Mayo
authors.affiliation: Mathematical Sciences , Queensland University of Technology , Brisbane, Queensland 4001, Australia.
authors.forename: Scott W
authors.identifier: 0000-0001-5304-2384
authors.initials: SW
authors.lastname: McCue
authors.affiliation: Mathematical Sciences , Queensland University of Technology , Brisbane, Queensland 4001, Australia.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Moroney
authors.affiliation: Plant Protection Chemistry NZ Ltd , Rotorua, New Zealand.
authors.forename: W Alison
authors.initials: WA
authors.lastname: Forster
authors.affiliation: Mathematical Sciences , Queensland University of Technology , Brisbane, Queensland 4001, Australia.
authors.forename: Daryl M
authors.initials: DM
authors.lastname: Kempthorne
authors.affiliation: Mathematical Sciences , Queensland University of Technology , Brisbane, Queensland 4001, Australia.
authors.forename: John A
authors.initials: JA
authors.lastname: Belward
authors.affiliation: Mathematical Sciences , Queensland University of Technology , Brisbane, Queensland 4001, Australia.
authors.forename: Ian W
authors.initials: IW
authors.lastname: Turner
keywords: alternating direction implicit methods; coalescence; curvilinear; liquid drop; thin film