# How Can I calculate the Contact Line velocity in interface??

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 August 5, 2010, 12:48 How Can I calculate the Contact Line velocity in interface?? #1 Member   Join Date: Nov 2009 Posts: 48 Rep Power: 9 Hello, Can anybody tell me How can I calculate the Contact line Velocity in interFoam? I want to implement new Dynamic Contact Angle, and I need Contact line velocity for Ca. I would be so grateful if the expertise in OpenFOAM help me. Thanks Mehran

August 6, 2010, 03:24
#2
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Sebastian Gatzka
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Quote:
 Originally Posted by farhagim Hello, Can anybody tell me How can I calculate the Contact line Velocity in interFoam? I want to implement new Dynamic Contact Angle, and I need Contact line velocity for Ca. I would be so grateful if the expertise in OpenFOAM help me. Thanks Mehran
Quick brainstorming:

Find the face (and its coordinates) on the contact surface occupied by the interface at the current timestep (for example where VOF = 0.5)
The spatial difference to the previous timestep will be the displacement of the interface. In addition with the timestep you will get the displacement velocity - the contact line velocity.
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August 6, 2010, 12:20
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Hello Sebastion.

Thank you for your answer. but The contact line velocity is the intersection between liquid surface and the solid surface. So I think I should find the cell with alpha=0.5 near surface and find the velocity or find the displacement of the interface and so on. Which one do you think better? Actually I am kind of new in Openfoam and I have a problem to recognize the all variable defined in interfoam ie. nHat or AfnHat ...
some times its hard to find what they come from. Would you please give me some hint in code How can I define the interface?

Thanks,
MEhran

Quote:
 Originally Posted by sega Quick brainstorming: Find the face (and its coordinates) on the contact surface occupied by the interface at the current timestep (for example where VOF = 0.5) The spatial difference to the previous timestep will be the displacement of the interface. In addition with the timestep you will get the displacement velocity - the contact line velocity.

August 6, 2010, 12:47
#4
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Sebastian Gatzka
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Quote:
 Originally Posted by farhagim So I think I should find the cell with alpha=0.5 near surface and find the velocity or find the displacement of the interface and so on. Which one do you think better?
Hm, interesting idea to interprete the velocity in the cell itself as the interface velocity. What do the other interFoam users think?
I think this may be appropriate at the proximity to the solid surface ... but I'm not 100% sure.

Quote:
 Originally Posted by farhagim Actually I am kind of new in Openfoam and I have a problem to recognize the all variable defined in interfoam ie. nHat or AfnHat ... some times its hard to find what they come from. Would you please give me some hint in code How can I define the interface?
In my option the interface is defined as alpha = 0.5.

The variables you mentioned have something to do with the normal direction of the interface.
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August 6, 2010, 13:14
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Thanks again for your quick answer. one very basic question: forexample: tell me what should I write in code for defining the cell filled with alpha=0.5. Sorry I know its stupid but I am new .

Quote:
 Originally Posted by sega Hm, interesting idea to interprete the velocity in the cell itself as the interface velocity. What do the other interFoam users think? I think this may be appropriate at the proximity to the solid surface ... but I'm not 100% sure. In my option the interface is defined as alpha = 0.5. The variables you mentioned have something to do with the normal direction of the interface.

August 7, 2010, 04:01
#6
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Sebastian Gatzka
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Quote:
 Originally Posted by farhagim Thanks again for your quick answer. one very basic question: forexample: tell me what should I write in code for defining the cell filled with alpha=0.5. Sorry I know its stupid but I am new .
Looping over all cells will be something like this:

Code:
```forAll(cells, cellI){
}```
cellI will then point to the current cell.

Inside the loop forAll-loop you will have to check for the interface.

Finding the interface with alpha = 0.5 may be a bit more difficult because the interface may not have an exact value of 0.5, but will be in between 0 and 1.

You should make a thread about this in the Programming section of this forum, because I'm not sure at the moment how to check for the alpha-value of the cell.
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August 9, 2010, 11:55
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Thanks for your help Sebastion. Yeah I have to make a thread to ask about this too.

Quote:
 Originally Posted by sega Looping over all cells will be something like this: Code: ```forAll(cells, cellI){ }``` cellI will then point to the current cell. Inside the loop forAll-loop you will have to check for the interface. Finding the interface with alpha = 0.5 may be a bit more difficult because the interface may not have an exact value of 0.5, but will be in between 0 and 1. You should make a thread about this in the Programming section of this forum, because I'm not sure at the moment how to check for the alpha-value of the cell.

 October 7, 2010, 09:49 #8 Member   Duong A. Hoang Join Date: Apr 2009 Location: Delft, Netherlands Posts: 93 Rep Power: 10 Hi Farhagim, I am also very interested in checking the velocity and location of the interface. I guess what we can do is getting the location and the value of alpha at every points then make the interpolation for alpha = 0.5 to get the location of the interface every time step. However, since I am a newer also, I do not actually know how to do it yet. Did you find success in getting it? Duong

 October 7, 2010, 19:49 #9 Member   Lars Kiewidt Join Date: Sep 2009 Location: Germany Posts: 54 Rep Power: 10 So, what I do to get the interface (and the positions of a moving bulk which are important for me) is just sampling the whole alpha1 field. Then I use MATLAB to find the values of alpha1 between 0.4 and 0.6 and finally get the interface. I think you can do this with a regular shell script, so you don't have to touch the OpenFOAM code. Hope that helps! Best regards, Lars

 October 8, 2010, 03:52 #10 Member   Duong A. Hoang Join Date: Apr 2009 Location: Delft, Netherlands Posts: 93 Rep Power: 10 Hi Lars, That is what I did at this moment. I wrote both Matlab script and Paraview python to get the position and velocity of the interface in post-processing. However, what I want to do now is getting the position of the interface during my simulation to implement my model. Then I got troubles with how we define x, y, z, alpha of every grid point and the communication between cell and cell (for instance how can we know the value of the neighbor cell). If you have any experiences about these, please let me know. Thanks. Regards, Duong

 May 10, 2011, 23:25 contact line velocity #11 New Member   pitambar randive Join Date: May 2011 Posts: 1 Rep Power: 0 dear i want to know how contact line velocity is different from bulk velocity and which formula can be used I am thinking that KWOK (2004) would be proper to use I want your comments

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