momentum wall boundary condition in unstructured grid
 

Dear friends:
I am reading Ferziger and peric 's book "computational methods for fluid dynamics". I am confused by the implementation of impermeable wall BC for the momentum equation in Page257.
since there is no convective fluxes, only diffusive fluxes need to be computed.
we also require that the matrix for u-momentum and v-momentum are the same.
Could you please give me some detail about the implementation process.
i am confused.