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Moving contact line in OpenFOAM

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Old   October 18, 2019, 08:56
Default Moving contact line in OpenFOAM
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Hi everyone,

I'm trying to understand how OpenFOAM, and interFoam in particular, deals with a moving contact line, e. g. a drop spreading over a surface. I've seen how the contact angle is imposed calculating the interface normal vector in the interfaceProperties.C file, but I haven't been able to find how OpenFOAM "makes the magic". I thought that maybe it would apply some external force, but in the UEqn.H file there is nothing like that.

I'm starting to think that it would be related to the surface tension force, but I'm not sure. I hope you can help me to figure this out.

Regards,

Adolfo
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Old   October 21, 2019, 09:06
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Hi dolfus,
As I know there are to two numerical method to simulate moving contact line in Navier Stokes equations: 1. Modify the slip velocity by the contact line velocity. 2. Add the external force to surface tension tension force at the vicinity of the contact line. You can read this article "VOF simulations of the contact angle dynamics during the drop spreading: Standard models and a new wetting force model" for the 2nd method.
I do not use OpenFOAM for moving contact line model so I can not help you this part.
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Old   October 22, 2019, 03:58
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Thank you for your reply. I know about this paper but the point is that I haven't been able to find anything like that inside the OpenFOAM code, probably because I haven't looked at the right files yet.


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Old   March 1, 2020, 18:31
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dolfus, have you found the scripts that deal with the contact line?
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Old   March 2, 2020, 11:38
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I always thought that in interfoam the "dynamic contact angle" is a result of the momentum equation. One con only specify the gradient of alpha at the wall. How the interphase evolves is that a result of the momentum equation.
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Old   March 2, 2020, 12:36
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Quote:
Originally Posted by mAlletto View Post
I always thought that in interfoam the "dynamic contact angle" is a result of the momentum equation. One con only specify the gradient of alpha at the wall. How the interphase evolves is that a result of the momentum equation.
Thanks for the response. See, I'm trying to see how to disable the contact line/angle models, forcing a system into a true no-slip flow. Do have have any ideas how to model this?
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Old   March 2, 2020, 17:06
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What do you mean with true no slip condition? Did you try a zero gradient condition for alpha?: you will not have an influence of the wall since you interpolate from the inner domain
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Old   March 3, 2020, 02:36
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Quote:
Originally Posted by mAlletto View Post
What do you mean with true no slip condition?
I refer to the (typically non-physical) condition that liquid-gas-wall interfaces do not move. In this way, liquid-gas interfaces can change configurations, but liquid would never spread.

Quote:
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Did you try a zero gradient condition for alpha?: you will not have an influence of the wall since you interpolate from the inner domain
Yes, but zero gradient still allows the liquid to advance/recede.
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Old   March 3, 2020, 03:03
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If you want the interphase to be at a fixed position you can use a fixed value boundary condition for alpha at the wall. Where initially it is zero you set it to zero and where it is one you set it to one
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Old   March 3, 2020, 05:00
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Quote:
Originally Posted by joshmccraney View Post
dolfus, have you found the scripts that deal with the contact line?
In the interfaceProperties.C file, you can find the method to impose the contact angle at any wall patch, and also you can see how the gradient of alpha following the normal direction to the wall is specified.
In the alphaContactAngleFvPatchScalarField.C file, there are several cases defined depending on your keyword "limit" in the alpha.water file.
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Old   March 4, 2020, 12:30
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Quote:
Originally Posted by mAlletto View Post
If you want the interphase to be at a fixed position you can use a fixed value boundary condition for alpha at the wall. Where initially it is zero you set it to zero and where it is one you set it to one
Can you elaborate on this please?
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Old   March 4, 2020, 14:20
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Hm If you want the interphase not to move at the wall you have to fix the value at the wall.
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Old   March 4, 2020, 17:27
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Quote:
Originally Posted by mAlletto View Post
Hm If you want the interphase not to move at the wall you have to fix the value at the wall.
Sorry, I guess what I meant is how do you set a fixed value boundary condition for alpha at the wall?
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Old   March 4, 2020, 18:15
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https://www.openfoam.com/documentati...xed-value.html
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Old   March 9, 2020, 17:26
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Quote:
Originally Posted by mAlletto View Post
Perfect, and thanks!

However, it seems we are missing some crucial information about the contact line, specifically the static contact angle. In real life, a liquid is always given an static contact angle. Any idea how to enforce this while also pinning the contact line?
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Old   March 10, 2020, 12:23
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Hey there,

May be you should take a look at "alphaContactAngle".

for dev version : https://github.com/OpenFOAM/OpenFOAM...hScalarField.H
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