Some question about channeloodles and average value
 

Hello everyone, I am Pei and I am still a fresh guy in foam world. Now I am testing some simulation with cyclic boundary and so take the channel oodles case as a reference.

Before I see that case, my previous setting is just creat a vector field of pressure gradient with fixed value (0 -0.0001 0)in the domain and add this term in the equation of the solver( turbfoam), and I found the method in channel oodles is much profesional and sophiscated. I try to understand the phsycal meaning of the periodic settings in this case but cannot find any introduction in guid documents. And it's difficult for me to understand them only with the comment in the code. Would any one like to introduce phsycally about this settings and the meaning of the Ubar? I will be appreciate for this very much.

And the same as the field average functions, the meaning of prime2mean?

Another question is the physical meaning of empty boundary conditions. What will happen if I put a empty boundary in a 3D simulation(thick enough, not as slim as the icoFoam case), e.g. compare to symmetry.

By the way, is there any one doing the simulation in the attachment? For long time I cannot got a reasonable result.(Osilating with stange patterns and varied to different patterns with different cube geometry properties)