Tandem arrangement

I need some help about the following two questions.
1.I develop a code for tandem arrangement of circular cylinders using the extrapolation boundary conditions proposed by Z.Guo et al. I run the code and i found that the vorticity contours shows some disturbance and after 100000 time steps if i run for more longer time it shows that the same behavior like before 100000 time steps. Can any one know why it’s happened.
2. I run a code for single circular cylinder for Re=100, i found that there is no lift coefficient, but then i try to to one grid size above in the y-direction the center of cylinder in y-direction, then the lift coefficient occurs. Is this also happened using the LBM.
Thanks and regards

in a flow with a symmetry axis, there can be no lift in a direction normal to this axis. it looks like you broke a symmetry by displacing the cylinder by one site. if the boundaries parallel to the direction of the lift (“the x-axis”) are periodic, and the inlet and outlet respect this symmetry (e.g. constant profile, pressure boundary, neumann condition), then there is no reason for a lift force to appear when you displace the obstacle. but if your boundaries are for example no-slip, then moving the obstacle away from the center breaks the symmetry, and the occurrence of the lift is expected.