A periodic boundary condition means that (for instance) the xmin and xmax values must be the same. The idea is that you’re looking at a small piece of a quasi-infinite domain. In practical terms, you copy the data from one side of the simulation to the opposing side. Reflect --almost-- works, but the data in the interior of the simulation may not be symmetric.
If you want to construct this using existing filters, you can do it with a bunch of Transform filters that only translate the data. In the image I’ve attached, that’s what I did. I think it’s possible to do this more efficiently (since every operation on the data only really needs to be run on the original dataset with ghost cells). Moreover, it’s tedious to set up, and you get weird visual effects at the boundaries (2nd image)
