[leroyv]

Dear foamers,

I need to solve problems with cyclic BCs 'all around the place'. To be clearer, this is the geometry I am considering:
https://www.dropbox.com/s/amuzikceam...nder_array.png

On this screenshot, the colouring is the velocity (U) magnitude, U being obtained using the simpleFoam solver and a uniform inlet BC on the x = 0 face. What I want to do is simply simulate the flow in the (6,4) cell using periodic boundary conditions:
https://www.dropbox.com/s/v5nz4mvx6user06/6-4_cell.png

Firstly, let's have a look at what we want to reproduce. Here are the velocity magnitude and orientation in the (6,4) cell (let's call this the reference problem):
https://www.dropbox.com/s/8eivt2e1ai...eference_U.png
This velocity field seems periodic. If we subtract a periodic field from this one, we should get another periodic field, maybe better as an evidence. So we do that and plot the so-called deviation field, UTilde, obtained by subtracting the volume average of U (which is constant over the cell) from U:

UTilde = U - UAverage

Here is what we get:
https://www.dropbox.com/s/8gnccd1pzy...nce_UTilde.png
This deviation field is periodic 'x-wise' and 'y-wise'.

I tried to simulate the flow in the (6,4) cell using the simpleFoam solver (though if might not be the best, AFAIK; anyway, this is not the worst problem here). I therefore simply applied cyclic patches at the boundaries of the cell. Although this insufficiently constraints the problem, the SIMPLE algorithm converges to a solution which only depends on the initial condition, yielding the following velocity field:
https://www.dropbox.com/s/rufn5k53mf...periodic_U.png

Given that image, we can doubt that this field is periodic. The deviation field gives a clearer proof:
https://www.dropbox.com/s/nf81rnnj4h...dic_UTilde.png
UTilde is not periodic, while it should be.

So here is my question: Is there any reason why the periodic BC wouldn't be satisfied in the cyclic problem? Did I do something wrong?

The associated OpenFOAM cases come attached. Screenshot gallery:
https://www.dropbox.com/sh/hmq2qx6jcvjc6lx/LFKCB1X32b