I think there is no need to specify an interface boundary condition, you first should patch a region as water (secondary phase) in your pipe and then you just set the conditions of inlet air in the hole boundary.

Which solver do you use? The interFoam and the likes do not specify the interfaces explicitly, they use the phase fraction fields.

You have to set the alpha (or gamma) parameter in that boundary (similar to breaking of a dam in User Guide) and the inlet velocity to that hole. Its easier to set boundaries if you have a separate geometry boundary(e.g line/surface) so that you can set the parameters to that whole boundary as air inlet.

For more advanced boundaries search for groovyBC before creating a custom boundary..

The Interface is evolved by the transport equation of volume fraction. You don't need to define specific boundary conditions for the Interface in OpenFOAM. For a drop or a cube of liquid inside the computational domain, you just use the command `setField` to define the scale, location and velocity of the liquid.

@Xinggang Li. This is true in the internal field (such as breaking of a dam with setField) and e.g in wall/outlet boundary conditions (see ship hull examples with waves). However in the "inlet" boundary, which is probably the case here, you must specify the volume fraction via alpha or gamma (depends on the version of OF) in order for the solver to know the quantity that "enters" the domain and evolve this (e.g create bubbles).

Specify the volume fraction in the 0/alpha file and then use setFields.

Probably you are talking about how to set up the interface condition in the walls. It is, the contact angle and the surface tension. Usually, when the capillary forces are not important, it is given as zeroGradient in the alpha1 file in the 0 folder. But in other cases, you should specify the value of the contact angle. The surface tension is given in the constant/transportProperties file. Take a look in the damBreak and capillaryRise tutorials of the interFoam solver.

Jignesh,

Which solver are you using for this application?

What does your geometric configuration look like? Your description of the "Air enters in to the pipeline from small hole and water is surrounding it" is not clear. Is the hole on the pipe wall and hence the air is as a jet in cross flow and breaks/detaches in to bubbles? Or is it introduced via a tube collinear with the pipe flow as a coflow? Such a description will help how to set up the problem in a certain way. In any case, let's start from interFoam, which might be appropriate in this case.

Assuming the air is introduce from the wall as a cross flow (here the velocity ratio could be high or low so doesn't matter), let's say you set your internal fields all liquid (hence alpha=1, continuous phase). Therefore, you need to specify the whole boundary condition as alphas=0, all gas). Now, you need to modify your transportProperties file under \constant, where you have to define the twoPhases appropriately (liquid continuous phase) and the corresponding sigma value. That should allow you to simulate such a configuration.

Hope that helps

I might be having a similar query. 

I need to simulate spiral concentrator with multiphaseInterFoam. However, in the OpenFoam tutorials all relevant cases are such that the fluid phases are already there in the domain. However, in my case I need a 3 phase continuous feed from the top which shall flow through the spiral profile. How do I set such inlet  boundary condition?