Hi all, I had a setup that one fluid is injected into another fluid to form a bubble or drop shape through an orifice.

It's pretty easy to set this up in fluent using vof model, which I am impressed. But I also found today that the surface seems have over-diffuse problem.

By saying diffuse, I mean, the surface is supposed to extend upward from oriface and form a bubble and detach ( which we had the solution using our home-made code), but using fluent vof, for whatever reason I can't tell, the surface keep stick with the wall(near orifice) and diffuse outward to cover the wall. It'll be easy to explain if I can post a picture here.

I heard this is one of the drawback of traditional vof, but I am not sure if this is the case with fluent or there might be a special settings I missed. I'd like to hear any suggestions.

Thanks. Best Regards Fang Jin

Did you use geo-reconstruct VOF scheme?

I forget to add gravity. Problem sovled. Fluent let you to set a wall-adhesion contact angle, but it has to be a constant.

[celebre17]

I am working on water free jet evolving into a quite air ambiance (vertical free jet)

I use VOF (volume of fluid) model to represent both water and air mixture. The goal of this study is to reproduce the jet break-up for instance the Rayleigh regime.

The domain of the calculation is a rectangular form to represent an axisymmetric form of a jet issuing into a domain.

The boundary condition of the test is as follow: inlet velocity at the jet injection. Three sides of the rectangular domain are used as pressure outlet condition and the forth side near the jet exit is used as axisymmetric axis.

I------------------------pressure-outlet------------------------I

I I

I I

pressure-outlet pressure-outlet

I I

----I I

inlet velosity I

----------------------------axisymmetric--------------------------I

The problem is: when I want to check the accuracy of the results I try to calculate the mass flow rate over the boundaries (inlet mass flow rate + outlet masse flow rate) which should be very small (vanishes in case of perfect calculation).

The results converge well (residue =10-6)

The result seems very realistic while the sum of (inlet mass flow rate + outlet masse flow rate) is very important

I guess that inlet mass flow rate must be in same order of outlet masse flow rate ( isn’t it???)

Please help me to explain this anomaly (is it an anomaly?)

Is there any other method to check the accuracy of the results using VOF.

[celebre17]

I am working on water free jet evolving into a quite air ambiance (vertical free jet)

I use VOF (volume of fluid) model to represent both water and air mixture. The goal of this study is to reproduce the jet break-up for instance the Rayleigh regime.

The domain of the calculation is a rectangular form to represent an axisymmetric form of a jet issuing into a domain.

The boundary condition of the test is as follow: inlet velocity at the jet injection. Three sides of the rectangular domain are used as pressure outlet condition and the forth side near the jet exit is used as axisymmetric axis.

I------------------------pressure-outlet------------------------I

I I

I I

pressure-outlet pressure-outlet I I

I I

----I I

inlet velosity I

------------------------------axisymmetric----------------------- I

The problem is: when I want to check the accuracy of the results I try to calculate the mass flow rate over the boundaries (inlet mass flow rate + outlet masse flow rate) which should be very small (vanishes in case of perfect calculation).

The results converge well (residue =10-6)

The result seems very realistic while the sum of (inlet mass flow rate + outlet masse flow rate) is very important

I guess that inlet mass flow rate must be in same order of outlet masse flow rate ( isn’t it???)

Please help me to explain this anomaly (is it an anomaly?)

Is there any other method to check the accuracy of the results using VOF.