[wasser]

Hello,
I am trying to simulate the deformation of droplet when it is carried by fluid flowing through a sudden contraction pipe.

My setup is as in attachment with very small dimension (in micron).

The diameter of the droplet is 1 micro so I made a very fine mesh to capture the deformation interface (element size is around <0.1 micron).

The problem here is because the small dimension, the velocity is very slow, hence if I took a very small time step (explicit vof), I have to wait forever. But when I used implicit vof, the vf-phase cannot be converged.

Finally, I made some assumptions such as: the droplet should have the same velocity as the carrier fluid at every time step. Therefore, I decided :
1/ Calculating the velocity profile at steady state of the carrier fluid and then
2/ Disable the flow equation (only consider the volume fraction equation) and patching the droplet phase
3/ Conducting the vof without initialization (to use the same velocity profile),

With this method, I can assign a higher time step even with explicit and the droplet moved and deformed.
However other problems appeared, when I try to investigate the effects of viscosity ratio and the surface tension, it seemed these parameters were not considered in the model at all. I meaned I changed the viscosity and surface tension, but the results are the same for every value of them.

Would you please give me some suggestions to solve this problem? Is my assumption ok? Do not consider the flow equation in vof is fine ?

Thank you very much

[wasser]

Does anyone have suggestions? I got stuck here (