Can diffuse-interface models quantitatively describe moving contact lines?

2011 ◽  
Vol 197 (1) ◽  
pp. 37-46 ◽  
Author(s):  
P. Yue ◽  
J. J. Feng
Keyword(s):  
Diffuse Interface ◽  
Contact Lines ◽  
Interface Models ◽  
Moving Contact ◽  
Moving Contact Lines

Sharp-interface limit of the Cahn–Hilliard model for moving contact lines

2010 ◽  
Vol 645 ◽  
pp. 279-294 ◽  
Author(s):  
PENGTAO YUE ◽  
CHUNFENG ZHOU ◽  
JAMES J. FENG
Keyword(s):  
Contact Line ◽  
Diffusion Length ◽  
Slip Length ◽  
Sharp Interface ◽  
Diffuse Interface ◽  
Contact Lines ◽  
Sharp Interface Limit ◽  
Interface Models ◽  
Moving Contact ◽  
Moving Contact Lines

Diffuse-interface models may be used to compute moving contact lines because the Cahn–Hilliard diffusion regularizes the singularity at the contact line. This paper investigates the basic questions underlying this approach. Through scaling arguments and numerical computations, we demonstrate that the Cahn–Hilliard model approaches a sharp-interface limit when the interfacial thickness is reduced below a threshold while other parameters are fixed. In this limit, the contact line has a diffusion length that is related to the slip length in sharp-interface models. Based on the numerical results, we propose a criterion for attaining the sharp-interface limit in computing moving contact lines.

A numerical investigation of the propulsion of water walkers

2010 ◽  
Vol 668 ◽  
pp. 363-383 ◽  
Author(s):  
PENG GAO ◽  
JAMES J. FENG
Keyword(s):  
Two Dimensions ◽  
Diffuse Interface ◽  
Viscous Force ◽  
Contact Lines ◽  
Moving Contact ◽  
Element Simulation ◽  
Thrust Generation ◽  
Moving Contact Lines ◽  
Recovery Stroke ◽  
Fishing Spiders

This paper presents a finite-element simulation of the interfacial flow during propulsion of water walkers such as fishing spiders and water striders. The unsteady stroke of the driving leg is represented by a two-dimensional cylinder moving on a specified trajectory. The interface and the moving contact lines are handled by a diffuse-interface model. We explore the mechanism of thrust generation in terms of the interfacial morphology and flow structures. Results show that the most important component of the thrust is the curvature force related to the deformation of the menisci and the asymmetry of the dimple. For water walkers with thick legs, the pressure force due to the inertia of the water being displaced by the leg is also important. The viscous force is negligible. An extensive parametric study is performed on the effect of leg velocity, stroke depth, leg diameter and surface wettability. The propulsive force is insensitive to the contact angle on the leg. However, the hydrophobicity of the leg helps it detach from the surface during the recovery stroke and thus decreases the resistance. It is also important for averting or delaying penetration of the interface at large rowing velocity and depth. In two dimensions, surface waves are more efficient than vortices in transferring the momentum imparted by the leg to the water.

Sign in / Sign up

Export Citation Format

Share Document