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DarrenC February 23, 2010 00:21

Fluent converting 'wall' to 'interior' BC for hybrid mesh
Hi everyone,

I am having a problem converting a 'wall' boundary condition in between my mesh interface of my hybrid grid to type 'interior'. I have a mesh interface surface in between my hex and tet mesh. When I imported my mesh into fluent, the interface becomes 2 different boundaries (foil and foil-shadow). When I try to change any one of these boundaries from a 'wall' type to a 'interior' type, The following error message occurs :

'Cannot change foil-shadow to interior because adjacent cell threads are of different types.'

The message is quite clear but I fail to understand why it is a problem. I have done this in a 2D geometry before and it worked fine but now I am working on a 3D geometry and it throws up this error.

FYI i use ICEM to do my grid and I use edit mesh>merge nodes>merge meshes to merge my tet and hex mesh together.

Could this problem be due to ICEM not merging the interface properly, or is it just Fluent not being able to handle interfaces where mesh elements are of a different kind?

Hope someone can shed some light into this for me.

Thanks in advance


-mAx- February 23, 2010 03:18

Check your 2D model (which worked fine) because what you are trying to do isn't possible, and it should also fail in 2d (as in 3d).
The only possibility to connect 2 non-connected-Mesh, is to work with interfaces.
So define your interfaces as INTERFACE Boundary Type, and then in fluent your have to set them: define/interface

DarrenC February 23, 2010 03:40

Hi Max

Thanks for your reply. As for my problem, I have just found it and it is a really silly one. I have one zone defined as solid and the other one as a fluid. =)

As for my mesh, the mesh from both zones are connected at the nodes and edges, so i did not use an interface.

Thanks anyway


alejandro_1980 November 19, 2011 07:04

yes it can be done
well, you can convert a unnecesary wall solid boundary result of the coupling between two volume meshes with the fuse faces tool of fluent. in case that you have just one unnecesary face, you can slit that face with slit face zone command, then, you r going to have two faces in the same positions, after that, you can fuse that two faces to form an interior unique face.. cheers =)

Traction April 9, 2014 08:52


i had a similar problem and found an easy solution to this issue.
i work with ICEM (for CFD) and generated a hybrid mesh consisting of a tet refinement area and a hex farfield - between them i used surfaces to build a conformal interface in ICEM.

fluent sorted this surfaces as an interface boundary - but to create a regular interface boundary you need more than 1 surface (can lead to potential problems in icem).

after finishing the mesh in ICEM i deleted the not required surfaces and sent the mesh to fluent.

afaik this works well for that kind of hybrid mesh !

chandrasekhar April 23, 2014 17:52

does anyone know how to impose a wall boundary condition on the interface between two bodies.My setup is as follows,
it has two bodies. it consists of a hollow aluminium pipe which has an inlet an and outlet, the other body is a copper rod which is partially inserted in the middle of the aluminium pipe and acts as an obstruction. i am doing this in 2D.

when i imported the mesh in Fluent and ran the simulation, fluent considered the common boundary as interface and the flow went through the copper obstruction. Do i have to impose some condition in the the Mesher for the fluent to recognize it as a wall. Any help on this would be greatly appreciated. Many thanks for replying.

with regards
Chandra sekhar

iciftci.42 November 6, 2014 06:00

thanx for reply.. :)

dewey November 15, 2016 11:01

I am donig a mesh with fluent and i want to import to openFoam, but when i use the comand fluent3D... the interfaces become to wall, and i want as interior.

This is what i have at the end of my .msh file

(12 (6 1 44e8 1 4))
(12 (a 44e9 8368 1 4))
(12 (7 8369 c1e8 1 4))
(45 (1 wall wall-entrada)())
(45 (2 wall wall-salida)())
(45 (3 interior interior-entrada)())
(45 (4 interior interior-porosity)())
(45 (5 interior interior-salida)())
(45 (6 fluid entrada)())
(45 (7 fluid salida)())
(45 (10 solid porosity)())
(45 (11 wall wall-porosity)())
(45 (12 velocity-inlet inlet)())
(45 (13 pressure-outlet outlet)())
(45 (14 wall paredentrada)())
(45 (15 wall paredporoso)())
(45 (16 wall paredsalida)())

i want to know if there are an easy way to do this.

thanks for you time.

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