outflow reflection

Hi all
I am trying to simulate a flow around a cylinder, but I have a problem of reflection at the outflow.
can someone help me please.

we can resolve this problem by adding an periodicity condition along the fluid direction.

If you download the latest Palabos release v1.4r1, you can find under :


an example of an external flow around an obstacle with an improved outflow boundary condition. The outflow treatment comes in two stages. An efficient outlet boundary condition called “VirtualOutlet” is imposed, and also an “absorbing zone” near the outlet, called “ViscositySpongeZone”, is applied.