I'm trying to set up a 3d sliding mesh problem to model a body moving past another body. I have each solid body inside its own box shaped fluid domain, with the two fluid domains adjacent to each other and touching for part of the length (imagine placing one shoe box on top of another, then sliding the top one a few inches along its length).

I've tried creating this as a single grid with multiple cell zones, making sure that each cell zone has a distinct face zone on the sliding boundary. I've also tried creating separate grid files, then merging them together in TGrid. With either approach, I've given the interface surfaces an "interface" boundary condition, and the grids look fine when displayed in Fluent 5. But when I try to define the interface, I get the following error:

"%create-grid-interface: not a pair"

I get the identical error with the single grid approach and with the merged grid approach. Does anybody have any suggestions? Many thanks.

Don't merge them together. Just operate "grid interface" in fluent, then try it. I am not sure.

hello

I think you should give a different boundary condition for each face of your interface in gambit and built the interface condition in fluent

Best regards

As I thought, my problem was extremely easy to fix, just hard to figure out. When specifying an interface, one gives it a name, so it can be managed if there's more than one. I was inputting "Main Interface" which caused the error simply due to the space in the name! Once I thought to try it without the space, it worked without a hitch. Too bad the error message wasn't at all descriptive of the problem.