Poiseuille flow in parallel plates

I simulated POISEUILLE TWO-PHASE FLOW in parallel plates with shan-chen model of lattice boltzmann method.
we have wetting phase flows in the region near the wall and nonwetting phase flows in the central region.
i used periodic boundary condition in the inlet and outlet boundary and nonslip(bounce-back) boundary condition were applied in upper and lower plates. The kinematic viscosity for nonwetting and wetting fluids is identical. more details are as follows:
body force = 1.5E-8
kinematic viscosity for both phase = 0.1667
viscosity ratio = 1/12
relaxation time for both phase = 1
the mesh used in simulation = 100*200
saturation of wetting flow = 0.5
my problem is velocity profile so that in the center line it is up to 10 times smaller than the desired velocity. But the speed is right in the wetting phase near the wall.
I wrote my code with fortran.
Does anyone know what my problem is?
thank you