Mesh effect problems

Hi everyone,
I am simulating multiphase flows using the Shan Chen method. Currently I’d like to mimic the fluid displacement in a triangular tube by introducing a pressure difference. You can see my results in the following video:
As you can see, in the upper right video there is an slice of the tube showing the triangular cross section. The problem I find is that red phase tends to go to the right corner due to the rectangular mesh and no symmetry is observed… I’m applying bounce back conditions on the walls. Do you have any clue how to avoid this undesired mesh effect? Any idea is welcomed! Thanks. And if you need more information don’t hesitate to contact me!