[MechEngr86]

I am new to CFD and while I have managed to figure out the million or so questions I have had there is one thing I cannot for the life of me figure out. I am modeling a container holding water using VOF. I have tried to simplify the model by having the fluid just sit there and do nothing. The idea is I will start adding complexity as I go. When I do this the water "explodes" out of the container and seems to ignore gravity as it hangs in the air and swirls. I am starting to get the feeling that VOF, or something else in STAR CCM+, cannot handle still fluid as when I drop the fluid into the container it seems to behave. In order to model the problem I am working on I do need the liquid to start off motionless in the container and I do need the surface tension effects. Any thoughts?

Thanks!

[Simbelmynë]

Why do you need it to sit motionless for a period of time? If nothing is supposed to happen, then you have no need of simulating it since the state is already known.

I would suggest removing the surface tension and test the simulation, then if that works better you can add it gradually.

However, you will always play with rounding errors if you try to model a motionless system. Double precision might be important. I guess the pressure residual should also be very low in order to not initiate spurious motion.

[arjun]

Originally Posted by MechEngr86

I am new to CFD and while I have managed to figure out the million or so questions I have had there is one thing I cannot for the life of me figure out. I am modeling a container holding water using VOF. I have tried to simplify the model by having the fluid just sit there and do nothing. The idea is I will start adding complexity as I go. When I do this the water "explodes" out of the container and seems to ignore gravity as it hangs in the air and swirls. I am starting to get the feeling that VOF, or something else in STAR CCM+, cannot handle still fluid as when I drop the fluid into the container it seems to behave. In order to model the problem I am working on I do need the liquid to start off motionless in the container and I do need the surface tension effects. Any thoughts?

Thanks!

Is it a steady calculation or unsteady one?

In case of unsteady calculation, i know for sure that with body force weighted scheme you can do what you want to do. In fact this is my unit test for body force weighted scheme in Wildkatze solver.
I have tried it with fluent too and it works well.

Steady flow I am not sure because Wildkatze also goes crazy little bit and i did not have time to investigate it.

I did this for bubble column where after a while some air gets into the column of water which is otherwise still.