how do i define interface boundary condition in vof?

can you give more details about your problem please ?

I am simulating a oil-water stratified flow in a 6 inch diameter pipe. Inlet conditions are constant mass flow rate. Oulet conditions right now I am using as pressure outlet but hope that outlet would yeild better results. still have to find out that. But the main problem is how to difine the interface to get a clear stratified oil water flow.

Thank You

Well, first of all RTFM, it gives you some advice on that. But it comes down to the multi-phase model that you select and the differencing scheme. The geo-reconstruct scheme should give you the "sharpest" interface, but you need to run transient. And then you need to use the modified High Resolution Interface Capturing (HRIC) differencing scheme.

What is this "High Resolution Interface Capturing"? Is it some property in Fluent?

It is a differencing scheme that you can select for the volume fraction equation.

Thanks charles,

Yes I am simulating the transient case with geo-reconstruct scheme. The differencing scheme is first order. One more question should I need to solve for VOF every iteration or every time step? Solving VOF at every iteration is taking lot much computing time. What is the likely impact of doing both of them, any experiance?

Thanks.

I would imagine that you need to use the HRIC differencing scheme to prevent it smearing the interface, or do you refer to the time differencing? I've only experimented briefly with Geo-reconstruct, because it is computationally so demanding, but I would think that it would be OK to solve the VOF only at every time step. What I have found from running VOF analyses is that it is very demanding on grid quality. A grid that is fine for single-phase may not necessarily be OK for VOF.