Gravity effects in the retraction of laying liquid filaments

RAVAZZOLI, P. D.; GONZÁLEZ, A. G.; DIEZ, J. A.

Paraná

Congreso; Fluidos 2021 - XVI Reunión sobre Recientes Avances en Fı́sica de Fluidos y sus Aplicaciones; 2021

We study the axial retraction of liquid filaments resting over inclined solid substrates that arepartiallly wetted by the liquid. Due to this condition, each tip of the filament recedes and formsa bulged region (head ) that subsequently develops a neck region behind it. Later on, the neckbreaks up leading to a separated drop, while the rest of the filament restarts this sequence. Inthe horizontal case, this breakup process is symmetric and yields to a regular arrangement ofdrops. When the substrate is inclined, the gravity effects are different at each tip of the filament,thus modifying the retraction distance before each breakup as well as the tips velocities. Weprove that the relation between the contact angle at the tip, θ x , and the contact line velocity,v cl , is still described by the Cox?Voinox?Blake (CVB) boundary condition, which involvesthe combined effects of hydrodynamic and molecular dynamics. This condition is used in thenumerical simulations of the full Navier?Stokes equations, whose results are contrasted with theexperiments. We also show that the maximum retraction distance decreases (increases) respectthe horizontal case for the tip that recedes against (in favour of) gravity. This effect representsan useful mechanism of self positioning of drops to achieve a variable distance among them.