[tambeshakunt]

Hello,

I am trying to set up a simulation something similar to the image attached. Basically there is a cuboid channel of fluid with an inlet and outlet and the 4 sides have periodic conditions. A model of a section of a grate / grill is in the centre.

I am having trouble with the periodic BCs: despite setting them as periodic under interfaces, I am unsure what region boundary type to assign to them??Free stream, wall (with slip), or something else? This is my first time using periodic BCs in star-ccm+ so I just wanted to ask how the software treats these type of problems and if I need to modify my approach.

Thanks in advance.

[ping]

the key to your issue is in the naming - they are called periodic interfaces and not BCs and are not actually boundary conditions in the star lexicon. once you interface the two sides successfully the boundary type you previously assigned is ignored. it is however important in the case of a partial interface eg on a sliding boundary

[tambeshakunt]

Originally Posted by ping

the key to your issue is in the naming - they are called periodic interfaces and not BCs and are not actually boundary conditions in the star lexicon. once you interface the two sides successfully the boundary type you previously assigned is ignored. it is however important in the case of a partial interface eg on a sliding boundary

I see, thank you. And does star-ccm+ care about the two sets of periodic conditions touching (as shown in the image above)? Or would this lead to issues?

[LuckyTran]

That's fine. Sides can touch.

[tambeshakunt]

I've tried a couple of things, but still getting an output that the interfaces are not conformal (hence I assume the periodic BC failed).

I've tried setting the interfaces to be fully developed as well as internal, with a periodic type (translational). Should I be looking at contacts? Anything else? Thank you.

[ping]

conformal can refer to the surfaces used on either side not being identical in shape and area when the transformation is applied - so check your geometry is perfect or it could be if you are using surface repair or wrapping which can alter the geometry and should not be required for such simple geometry anyway

it can also apply to the mesh being conformal or the mesher having trouble achieving this feature

[tambeshakunt]

Originally Posted by ping

conformal can refer to the surfaces used on either side not being identical in shape and area when the transformation is applied - so check your geometry is perfect or it could be if you are using surface repair or wrapping which can alter the geometry and should not be required for such simple geometry anyway

it can also apply to the mesh being conformal or the mesher having trouble achieving this feature

Thank you, disabling the surface wrapper seems to have done the trick!