[3kha]

I have a long tank where a fluid is circulating as in the figure. The fluid travels towards -x on the bottom long edge, turns up at the left edge, towards +x on the top long edge, turns down at the right edge, and repeats.



The tank is very long, and I don't want to model the whole thing. What boundary conditions do I apply on the left and right edges? It is not periodic - the change in velocity at the left edge is (+i,+j) and at the right edge is negative of that. Thanks!