pressure outlet on side faces
 

Hi everyone,
I would like to simulate air and CO2 in a cube. B.C. for front face is velocity inlet and for rear face is pressure outlet.
CO2 should leave the cube, but the problem is CO2 reach side walls and go with air flow and leave the cube. If I set B.C. to pressure outlet for side faces, reversed flow will appear and solution does not converge.
Is there any way to set pressure outlet B.C. for side faces without reversed flow?
Or any solution that just CO2 pass through the side faces and air flow goes on?

Thanks for any help.