I am simulating multi-component Shan-Chen model in channel flow. My problem is outlet boundary condition. I am trying to implement Neumann Boundary condition at the outlet so that the flow can leave the domain. However, I am very confused that at which nodes I should implement Neumann Boundary condition i.e. 2nd last column or last column? Also, what is the difference if I apply Neumann Boundary condition before streaming or after streaming?