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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?



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

Nikhilcfd April 19, 2012 13:54


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.

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