[joshmccraney]

A VOF solver for contact-line problems typically need a model of fluid slip at the contact-line. Do you know how this is handled in interFoam for the constantAlphaContactAngle case?

[mAlletto]

What one does is effectively prescribing the gradient of alpha accordingly to the contact angle. I think the topic is also discussed in this forum

[joshmccraney]

Thanks for the reply. I perused the threads and searched for contact angle, but couldn't find any elaboration of what you said. Can you direct me further?

[mAlletto]

Here e.g. InterFoam contact angle

[joshmccraney]

Thanks so much, that thread was very helpful. One last question: how is the stress singularity at the contact line overcome/subverted?

Specifically, in finite-element numerical simulations the contact line stress singularity is easily handled by imposing a slip boundary condition (with its associated slip length) at the solid. This allows the computation to converge with grid size refinement. But how is this issue is resolved in VOF. I assume that VOF introduces an ad-hoc thickness to the interface, which eliminates the singularity that appears in "zero-thickness" interface approaches. But I wonder how to make the stress calculated with VOF all the way to the contact line converge with grid refinement.

[mAlletto]

Actually one does not have any singularity in the stresses resulting from a small curvature radius. The streamline deviding the two phases is not resolved explicitly in VOF. By the way modelling surface tension in VOF is still an open issue since representing the curvature is not so trivial. See e.g. https://arxiv.org/abs/2103.00870

[joshmccraney]

Originally Posted by mAlletto

Actually one does not have any singularity in the stresses resulting from a small curvature radius. The streamline deviding the two phases is not resolved explicitly in VOF. By the way modelling surface tension in VOF is still an open issue since representing the curvature is not so trivial. See e.g. https://arxiv.org/abs/2103.00870

Awesome, thanks so much! As it turns out, I have access to low-g capillary driven flows aboard the ISS. I've contacted the author of the archive you sent, as it would be beneficial to see if tTwoPhaseFlow does a better job than interFoam. Thanks for the direction!

Josh McCraney

[joshmccraney]

Originally Posted by mAlletto

Actually one does not have any singularity in the stresses resulting from a small curvature radius. The streamline deviding the two phases is not resolved explicitly in VOF. By the way modelling surface tension in VOF is still an open issue since representing the curvature is not so trivial. See e.g. https://arxiv.org/abs/2103.00870

To elaborate further, since I'm still a little confused, is there a relation between stress singularity at the moving contact line and the smallness of the radius of curvature? The existence of the singularity has been established for models that have all of the following: a) zero-thickness interfaces, b) constant Newtonian viscosity and c) no-slip. No other requirement needs to be added, and no other requirement can remove the stress singularity. Of course, diffuse interfaces, shear-thinning and slip can individually each eliminate the singularity. Right? I really appreciate your help here.