[Mohammadja]

Hi
I am trying to use ChtMultiregionFoam solver to simulate a problem, but I am not sure about the boundary conditions on the fluid-fluid interfaces, I have a sinusoidal BC for pressure at the inlet of Fluid 1 region( please see the attached document.)
I know about the boundary conditions on fluid- solid interfaces but I am not sure to use what type of BC between two fluid regions (Fluid 1 TO Fluid 2 and Fluid 1 TO Fluid 3 .)
I think zero Gradient doesn't work and it should not be true, I tried to use Calculated but the software (OpenFoam 5) gives me an error.
It is appreciated very much if you can help.
Thanks
MJ

[pete20r2]

I don't understand what a fluid-fluid boundary is. Is it a membrane boundary or do the three fluid regions form one continuum that fluid can move between?

[Mohammadja]

Originally Posted by pete20r2

I don't understand what a fluid-fluid boundary is. Is it a membrane boundary or do the three fluid regions form one continuum that fluid can move between?

Hi dear Peter
Thanks for the reply,
Probably the sketch misled you, sorry for the inconvenience,
Indeed, we have only one fluid here and there is no membrane, suppose air enters from the inlet and when it reaches to the solid it becomes two branches, one passing above the solid part and the other one passing below the solid part.
But as you know, if we want to use the ChtMultiRegionFoam, we have to define the regions, now my question is that if we define two fluid regions in neighbourhood (such as what you see in the sketch), what type of boundary condition in the common patch of two fluid regions should be defined?

I don't want to define unreal boundary condition at this patch because in reality we have one continuum for 3 fluid region,I think my question is very basic for people who used ChtMultiRegionFoam successfully, because frequently we have two fluid regions in neighbourhood...
Many thanks again
MJ

[pete20r2]

Ok, I understand now. You can either make the patches cyclic (non-identical patch) or do it the correct way and use mergeMesh and stitchMesh to get rid of the interfaces by making just one fluid mesh.
There are many guides on the forum for setting up both cyclicAMI boundaries or using the mergeMesh and stitchMesh utilities.

[Mohammadja]

Originally Posted by pete20r2

Ok, I understand now. You can either make the patches cyclic (non-identical patch) or do it the correct way and use mergeMesh and stitchMesh to get rid of the interfaces by making just one fluid mesh.
There are many guides on the forum for setting up both cyclicAMI boundaries or using the mergeMesh and stitchMesh utilities.

Many thanks dear Peter
I try to test the CyclicAMI.
Regards
Mohammad