I get stuck with setting the time step when using VOF model. If grid size is very small (1e-06 m) and model is unsteady, I am supposed to define a very small time step (dt < 1e-12 sec) in order to track interface of domain (using VOF model). Otherwise, if the time step is larger, the floating point error will display. It is incredible time step. How long will it take to run the model with total time of 1 sec or 10 sec?.

Anybody can give me some suggestion to deal with this problem? How can I do in Fluent in order to increase time step (for example: dt = 1e-6 sec)?

Thank you in advance.

can you please give me idea abut how can we trak the interface co-ordinates in VOF model. what UDF macro/function we need to use. thanks

I think that it is easy to use VOF model in Fluent. But the important issue is what you apply VOF for?. Actually, I do not understand what you want to ask. You should tell everybody here details what you want.