On the contact-line pinning in cavity formation during solid–liquid impact

Abstract

We investigate the cavity formation during the impact of spheres and cylinders into a liquid pool by using a combination of experiments, simulations and theoretical analysis, with particular interest in contact-line pinning and its relation with the subsequent cavity evolution. The flows are simulated by a Navier-Stokes diffuse-interface solver that allows for moving contact lines. On the basis of agreement on experimentally measured quantities such as the position of the pinned contact line and the interface shape, we investigate flow details that are not accessible experimentally, identify the interface regions in the cavity formation and examine the geometric effects of impact objects. We connect wettability, inertia, geometry of the impact object, interface bending and contact-line position with the contact-line pinning by analysing the force balance at a pinned meniscus, and the result compares favourably with those from simulations and experiments. In addition to adjusting the interface bending, the object geometry also has a significant effect on the magnitude of low pressure in the liquid and the occurrence of flow separation. As a result, it is easier for an object with sharp edges to generate a cavity than a smooth object. A theoretical model based on the Rayleigh-Besant equation is developed to provide a quantitative description of the radial expansion of the cavity after the pinning of the contact line. The accuracy of the solution is greatly affected by the geometrical information on the interface connected to the pinned meniscus, showing the dependence of the global cavity dynamics on the local flows around the pinned contact line. Vertical ripple propagation on the cavity wall is found to follow the dispersion relation for the perturbation evolution on a hollow jet.

Numerical Approaches to Complex Fluids

“…The Navier-Stokes/Cahn-Hilliard model has recently been adopted in several studies of immiscible fluids both in laminar and turbulent conditions, for example, Refs. [122,[125][126][127]. Besides the Cahn-Hilliard formulation, different phase-field methods have been proposed, based on alternative forms of the free energy, see, for example, [128] for compressible flows with phase change for cavitation problems.…”

Simulation of incompressible multiphase flows with complex geometry using etching multiblock method

“…When the drop becomes sufficiently large, a droplet breaks up from the drop and drips down under the influence of gravity. During the whole dynamic process, the contact lines are pinned at the corner of the pore, primarily due to the geometry-induced contact-angle hysteresis [26][27] . Figure 8 shows the snapshots of the periodic dripping process from the pore.…”

Sustaining Robust Cavities with Slippery Liquid–Liquid Interfaces

“…The entry of solid bodies into liquids is widely manifested in daily life and industrial activities. [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ] Generally, the formation of a continuous and sustained gas cavity surrounding solid surfaces that rectifies the triple interface into a smooth liquid‐gas interface is highly preferred because of many advantages, such as drag reduction and modulation of heat transfer. [ 9 , 10 , 11 , 12 , 13 , 14 ] To maintain the gas cavity, two approaches have been widely developed: either the use of external heating [ 15 , 16 , 17 , 18 , 19 ] or the design of hydrophobic surfaces.…”