use of periodic bc

subhra

When one applies periodic bc to velocity and pressure, it is said : "End section of domain wraps up with start section of domain.."..is it ok to think that the domain is in the shape of a loop? Even if I don't use any co-ordinate transformation to unwrap the physical shape of the loop (say a donut) into the geometry of simulation (in my case, plane channel) ?

..any advice/comments on this will be greatly appreciated...

actually I simulated a plane 2-d channel (containing an electrohuydrodynamic flow generating element) using periodic bcs to velocity and pressure at inflow and outflow...but I am not clear to what extent does it make sense to interpret this as a flow loop pumped by the element...

the other interpretation I can think of is element is one of a streamwise series of repeating elements in a developed flow..but that's not what I want and further that will probably require a pressure drop?