How to use constant alpha contact angle in OF 2.1.1
Dear foamers,
I am trying to simulate splashing droplet on a surface by using interFoam, OF 2.1.1. The problem is I did not get the same behavior for the experiment results. I did not use alpha contact angle, do you think it the problem? and If it is, how can I use it? Please help me because I am new in OF. Sandy, 
Hi Sandy,
I guess you used the zeroGradient BC? That is indeed going to give pretty different results. To use the constantAlphaContactAngle BC you need to specify it in 0/alpha1 on the patch where you want it like this: Code:
walls That said, I am pretty sure that the constantAlphaContactAngle BC is not going to work well either, because your problem is highly dynamic and the contact angle that you model should thus dependent on the local velocities. 
Quote:
Thank you so much for your response, I appreciate it so much. I took your advice and recommendation about my case..splashing bubble.. I implemented the boundary condition you recommended but with a theta0 = 163 , because I have a numerical study to compare with, any how, I did not get the same behavior as well as you expected. Please do you have any more suggestions about my case, do you think do I have to use dynamics alpha contact angle instead of the constant one. Any thoughts would help... Sandy,:confused: 
I indeed think you need to use the dynamicAlphaContactAngle BC or, even better, a more realistic implementation for the dynamic contact angle like the CoxVoinov model. The latter would require you to code it yourself, but it is not a difficult task.
What I am wondering is whether you could show the comparison for the constantAlphaContactAngle and your validation case, so we can get a feel for the difference. 
Quote:
I will change constannt to dynamic and see what happiness, but about changing the code model, I do not think I am cleaver enough to do it especially I am not any good in c++. If that is not that difficult, where shall I go to what dictionaries and what I have to change... If you can, just direct me when ever you have time. Sandy, 
hi,
is there anybody how can give us a idea of the realistic dynamic contact angle values thetaA R and thetaU, for waterairsolid contact ??? thanks a lot Laurent 
The dynamicAlphaContactAngle is not a physically correct model for the dynamic contact angle so it will be hard to give you values that lead to physically correct behaviour without fitting experimental data for your particular system.
Moreover, in general you cannot say which contact angle a waterairsolid system has without knowing what the solid is, because the contact angle (i.e. thetaA and thetaR) are determined by the chemical and physical nature of the solid as well as by the water and air interfacial properties 
1 Attachment(s)
Hi Michiel,
thank very much for reply, i understand dependance of solid surface. i would like if possible to predict a ventilation of a free surface piercing foil like on the picture attach. i presume this phenomena is related to the contact angle. very good question here, what is Uwall... http://www.cfdonline.com/Forums/ope...interfoam.html so should i give up with OF dynamicContactAngle ? try to build a Kistler model? for now, the "funny" think is that my simulation crash with a constantContactAngle BC, and run with a zeroGradient or dynamicContactAngle... thanks LL 
Quote:
I want to ask as well, how to specify the dynamicAlphaContactAngle BC, please? Can you give us an example? Many thanks. 
You can simply use
Code:
walls theta0 for the contact angle at 0 velocity thetaAthetaR the offset from theta0 at infinite velocity uTheta for how quickly the angle changes from theta0 to thetaA/thetaR (i just put in some random value) The mathematical implementation is: theta =theta0 + (thetaA  thetaR)*tanh(uwall/uTheta); Note that this is not a physically correct implementation of the dynamic contact angle, but for moderate velocity you can fit thetaAthetaR and uTheta to experimental data and might get away with using it. 
Quote:
Many thanks for your reply; So, each time, for each case, we have have to choose the thetaAthetaRtheta0 and uTheta according to experimental results, right? cheers m 
Quote:
I think the current exist model for dynamic contact angle is not so accurate, i so I decide to implement new alternative contact angle model for testing. cheers g 
Dear michielm
Again, may I ask you one more question. To use the dynamic contact angle model in interFoam solver, we only need to specify the boundary conditions at 0 initial time, but we do not need to modify the library source file interphaseProperties.C, right? But I don't see how the dynamic contact angle has been calculate in the interphaseProperties.C. Could you tell me how the dynamic contact angle link to and work in the interphaseProperties.C file? I see in ./transportiModel/twoPhasePropersities/, there exist a dynamicAlphacontactangle.C which contain the dynamic contact model. but I do know how this contact angle model been used in the interphasePropersity.C to update the interface propersities. many thanks cheers Ming Quote:

Quote:
Did you find the answer for your question, I want to know as well how is the link and how to ubdate the dynamic contact angle in OF. Regards, Sandy13 
1 Attachment(s)
Dear all,
I've been having some problems with a simple case, which basically consists in a droplet adjusting to a surface given a specific contact angle. I want to measure the time that it takes to stabilize after changing the contact angle of the surface. I tried all the boundary conditions (constant and dynamic contact angle with noFluxPressure on the wall) and nothing seems to work out. I attached the video (as a zip file) of one of the test cases. As you can see, as the droplet adapts to the new contact angle, it oscillate (as it should be). The problem is that it never stops oscillating. It looks like there is no viscous dissipation or something. Anyway, I belive that all my boundary conditions are correct. Maybe the dynamics in my problem are too strong and, therefore, the dynamic contact angle provided by OpenFOAM is not a good option in this case. Maybe I need to implement another contact angle model. But before I do that, I want to know if anybody ever saw those kinds of results before... By the way, I am using OpenFOAM 2.1.1. If you need I can post my boundary conditions here. Just answering the questions above: Ming: Yes, you only need to specify the boundary condition of dynamic contact angle on the 0/alpha1 file. The interfacePrperties.C makes the correction of the contact angle on the wall (as you can see in the function correctContactAngle() on the line 48 from interfaceProperties.C file) I belive that if you want to change the way the contact angle is calculated, you can just make some changes on the dynamicAlphaContactAngleFvPatchScalarField files. Thank you in advance! Cheers, Nico 
All times are GMT 4. The time now is 16:33. 