hello,

I have a train who enters a tunnel. There are 2 grids and one of them moves. Between the 2 grids is there are 2 interfaces. With me this are 2 lines (2D) who overlap. But if i want to make a grid interface it creates 2 walls automatically. I don't want the walls because my flow has to go through the interfaces. In the user guide 33.3.19 there is stated (at the Boundary Zone 1 and Boundary Zone 2 point) that "If the two interface zones overlap completely ..., no wall zones will appear." But with me they do. What is wrong?

Thanks for the help

greetings

Dieter

It is where the grids don't overlap that walls are created. You need to either make both grids very long so that if walls are created it doesn't affect the flow area of interest or use dynamic meshing instead of sliding mesh.

Either that or you aren't creating the interfaces correctly. They should lie in the same plane or line in 2d but share no nodes. Then in fluent under grid -> interfaces you need to create an interface and match the two up. Simple.

Thank you for your response Jimmeny. I 'm working with a dynamic mesh. I will have a look tomorrow at the university if the created walls are over the complet length or not, but i think so. I have made two seperate grids in gambit and joined them with tgrid. The fist and fixed grid is U form twisted 180°. The moving grid is a rectangle that fits perfectly inside of the U form. Than I read the joined grid back in to fluent and fused two legs of the U form with two sides of the rectangle. From this sides I make an interior because the nodes are shared. This works perfectly. But the top leg of the Twisted U and an another side of the rectangle should be interfaces. This two interfaces lay in the same plane. It is possible that some nodes are shared but certainly not all of them. Where could i have made a mistake?

Thanks a lot for the effort.

Dieter

take care that your interfaces don't share 2 different fluid zones. for instance if your interface has 2 adjacent fluid zones types, Fluent will automatically separates your interfaces into 2 distinct interfaces.

hello Max en Jimmeny and the others. When I have a look at the walls in display grid, I can't find them and the nodes are not shared. So i will continue my search for the answer.

Max when the grid is still seperated in gambit I make one interface for the first grid and one for the second. When they are seperated the interfaces only have on one side fluid. Is it this what you are explaining or not?

Greets Dieter

no, this is not what I explained. Let say you have an interface between 2 geometries: the right geometry and the left one. We are agree when I say that you have 2 interfaces which are coincident (one for the left geometry and one for the right). Now if for the right geometry your defined 2 distints fluid zones: let say fluid zone 1 and fluid zone 2, the interface for the right geometry will have 2 distincts adjacents cells. Once you import your mesh, Fluent will separate the interface your the right geometry into 2 interfaces because off 2 differents cell zones. But after that you won't be able to assign your interfaces (define/interface) but if you just have one fluid zone, than it doesn't match your case.

The problem is solved the walls were really created but they had no distance. My flow was just on the point of crossing the interface. Now already have a different problem he creates now negative volumes after some time steps.

Greets Dieter