I have implemented the 2D cylinder Poiseuille flow with the Lattice Boltzmann method, and I am using “on-grid bounce back” boundary conditions.

However, my velocity profile is strange. There is a finite velocity at the boundary, but I was under the impression that the whole point of the bounce-back BC was to ensure no-slip. My velocity profile looks like this.

Does this behavior at the boundary imply an error in my implementation?

I’d be happy to post my code, if anyone is interested in taking a look.

Thanks in advance,

Niles.