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 michielm April 18, 2012 13:10

interFoam with dynamic contact angle: distorted interface

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Hi all,
I am using interFoam to simulate a droplet rolling down a tilted plate. I started out using the static contact angle model and all seemed fine*.

Then I switched to the dynamic contact angle model, setting the parameters to get as close as possible to the Cox-Voinov relation.

This resulted in an unstable/distorted interface (near the contact line) as you can see in the attached image.

Does anyone know what might be the cause of this distortion which is clearly unphysical?

Thanks,

Michiel

* (except that the lack of dynamic CAs gave non-realistic terminal velocities)

 Nikhilcfd April 19, 2012 13:54

Hello,

Are you using the dynamic contact angle expression (theta0+ (thetaA-thetaR)*tanh(uwall/utheta) in OpenFoam? Non realistic (or non zero) velocities might be parasitic currents (which I think originates from curvature calculation). I am not sure why a Dynamic CA implementation would cause such a distortion. Did you use the same mesh for both the simulations. What did you input for thetaA, thetaR and utheta.??

 michielm April 20, 2012 01:34

I used exactly the same mesh, BCs and numerical schemes. The only difference is the static vs dynamic contact angle model.

I indeed used the standard implementation in OF and adjusted the parameters (thetaA-thetaR) and utheta to approximate the cox-voinov relation (theta_dyn=(theta0^3+100*Ca).^(1/3)).

The values I used for that where
- thetaA-thetaR=30.6 (thetaA=50.6 and thetaR=20 to be precise)
- uTheta=0.0255

 michielm April 24, 2012 01:40

I managed to solve the problem. In the end it turned out to be something rather trivial:
I had defined my thetaA and thetaR in the physically correct order (thetaA>thetaR), but had not noticed that the definition of uwall in openfoam depends on the surface normal, which switches sign depending on which phase I use as the droplet (alpha=1 or alpha=0).

I have now swapped the values of thetaA and thetaR and the system behaves as it should (at least numerically, physically I still have to check)

 IndrajitW December 20, 2012 08:54

Hi michielm,
I wish to start with the simulation of droplet rolling on an inclined plate.However I am new to OpenFoam and am lost where to start from??? I have done the Dam break cavity and now I wish to go for droplet rolling on inclined plate.Please guide as to where I may start.
Indrajit

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