I am simulating a simple two phase oil water flow usin VOF. can anyone tell appropriate boundary condition. I tried many but the result is not correct.

I have two inlets for oil and water separately, and one outlet for both of them.

the residuals are increasing after some iterations.

At the inlet I advise to use A CONTINUOUS VELOCITY, for example parabolique profiles coming from the fully developped flow in the duct.

Depending on the velocity and the viscosity, use boundary layer mesh at the walls.

Resolve well the area where the interface is likely to be present.

keep in touch

Thanks for your help but as I have two inlets one for each phase, should I have two separte velocity profiles to match with the oil and water inlets?

Regards

Some other points could be:

- Set your inlets as velocity inlets (not inflows) and remember to define the volume fraction of one of the phases in that boundary (good practice: the heavier one, that you have to define as 2nd in the "phases" panel): so in the water inlet define volume fraction of oil = 0 and ine the oil inlet define vf=1.

- Normally one sets a pressure boundary as outflow, and wants to know what volume fraction of the phase of interest will flow through that boundary in a prescribed time, but BE CAREFUL: you have to define the volume fraction of one of the phases even for a pressure boundary, so I would extend the domain past that point of interest until a "known" boundary can be applied...

- One more: are the pipes initially empty (filled with air, for example)? In this case you will need a third phase...

Hope this can help

Edi.

Do you have a free surface in your setup? Why are you using the VOF? may be you have to use the right mixing model?

I did the same way (setting the volume fractions as you have said) and I have some gud results to see but I am struck now at the calculation part of my desired flow rate and I hope your point makes some sense and I will try that. The pipe is filled with oil and water only and I dont have any third phase.

Regards.

I dont have a free surface but Fluent help manual for multiphase flows states that tat for stratified flows and near stratified flows I need to go for VOF, afterall VOF has a surface tarcking tools with it. ryt??

This is Your Original Query:

I am simulating a simple two phase oil water flow usin VOF. can anyone tell appropriate boundary condition. I tried many but the result is not correct.

I have two inlets for oil and water separately, and one outlet for both of them.

the residuals are increasing after some iterations.

Ahmed: I do not see neither a two phase flow (vapour and liquid or solid and liquid of the same matter) nor a stratified flow in your setup, you have one inlet for oil and a second inlet for water, and one exit for the resulting mixture, there is no chemical reaction, but there is a mixing process, you have to use the transport of species model, You do not even have a free surface, so why are using the VOF model. If this is a school project talk to your supervisor but if this is a industrial project then you have to talk to your support engineer but urgently.

It is an industrial project but yet it is a simulation of oil water two phase flow. Now regarding the mixture mine is a transient case and as time passes one would expect that the flow will be setteled with oil on top and water in the lower part of the pipe section, and just today I got the pattern I was expecting. My apologies for not mentioning tht it is a two phase LIQUID-LIQUID simulation.

Anyway thanks,

So it is a mixture (Oil and Water) flow not a two phase flow unless the definition of phase has changed since I graduated. Discuss the situation with your support Engineer, the easiest way to solve your doubts, it is a part of the license fee.

Read Tutorial 18 (Using the Mixture and Eulerian Multiphase Models)